Woodpeckers in urban environments:
A review on mitigating damage to
buildings
By: Stefan van der Wal
Abstract
Recently, woodpeckers have been observed to damage facades of buildings at several different
locations in the Netherlands. Insight into the mechanisms underlying this strange behavior of
woodpeckers is needed. Moreover, there is a need to identify solutions to mitigate the damage by
woodpeckers to facades of buildings.
It is suggested that competition regarding available high quality nesting holes might occur
between woodpeckers and secondary cavity nesters, such as ring neck parakeet Psittacula krameri
and the European starling Sturnus vulgaris (e.g. Aitken et al., 2002; Lohmus and Remm, 2005). This
might in particular be the case, when competition takes place in an area with a shortage of suitable
trees that can be used by woodpeckers for excavating cavities. As a result of competition and/or a
shortage of suitable nesting trees, woodpeckers might excavate nesting cavities in facades of
buildings.
In order to mitigate damage by woodpeckers to facades of buildings, it is recommended to
hang reflective ribbons on the sidings of buildings to frighten woodpeckers. Moreover, damage to
facades should be repaired as soon as possible with rigid, white or pastel colored materials. If a
shortage of suitable nesting trees might be an issue, it is suggested to provide woodpeckers with
alternative artificial nesting sites nearby (Jasumback et al., 1999). This could be done by placing nest
boxes, artificial or dead wood near the location where woodpeckers damage facades of buildings. In
case this is not effective, it is suggested to cover the facade of the building entirely with vinyl,
aluminum, aviary mesh, or plastic netting (Harding et al., 2007; Belant, 1997; Jasumbach et al., 2000).
In regards to park management it is suggested to conserve old, damaged and dead trees, as
these are important for creating and maintaining a sustainable breeding habitat for woodpeckers.
For future construction near forests, parks or wooden areas it is recommended to use rigid materials
that cannot be damaged by woodpeckers.
This document is a master thesis written in the form of a review article by Stefan van der Wal
(vanderwal.stefan@gmail.com) for the master programme Environmental Biology at Utrecht
University, the Netherlands. The writing of the thesis encompasses 7,5 ects and is accompanied by a
practical research report. The thesis was written under supervision of Dr. P. A. Verweij from the group
Energy & Resources at the Copernicus Institute of Sustainable Development. The thesis aims at
solving a problem posed by the municipality of Utrecht and was therefore also supervised by Hans
Kruse, environmental consultant of the municipality of Utrecht.
1
Introduction
Over the last decade, biodiversity concerns have been high on the list of conservation efforts all
around the world. The United Nations even declared the year 2010 the international year of
biodiversity. As a result they hoped the whole world would take action to safeguard the variety of all
life on earth. Biodiversity encompasses genetic and ecological diversity, but is mainly referred to as
species richness (Harper and Hawskworth, 1995). The fast decline of biodiversity is now a global
recognized problem and it is estimated that half of all current species face the risk of extinction in the
near future (Sax and Gaines, 2003).
One of the main threats of biodiversity is the worldwide increasing urbanization (Sochat et
al., 2010). Population growth and the proportion of urban residents increase every year and as a
result cities expand at the cost of nature. Some green areas can be found in cities, but city parks
primarily serve a recreational purpose and are often considered biological desert (Sandstrom et al.,
2006). Since biodiversity in urban environments does not only depend on natural processes, but also
concerns human activities (Kotaka & Matsuoka, 2002). Managers of urban forests and parks first
have to take the safety of visitors into account and biodiversity comes next. An indicator that can be
used to measure the intensity of management in a certain area is the availability of dead wood
(Nilsson et al., 2002). Old, sick or dead trees are normally removed from a city park, because falling
wood poses a potential safety risk for visitors. The effects of this way of managing are enormous on
the availability of nesting sites for species that use trees for nesting and can be responsible for
biodiversity loss in urban environments (Winkler et al., 1995).
Biodiversity is important for the quality of urban life, because it serves an educational
purpose for urban residents (Sochat et al., 2010). However, biodiversity in urban environments often
concerns undesirable species (Sochat et al., 2010). The overabundance of certain species can
sometimes even result in plagues since natural predators are often absent in urban environments.
Gulls and pigeons for example flourish in many big cities, but can be annoying for its inhabitants.
Conflicts with species can be challenging since dynamics of urban systems are totally different from
natural environments and are often poorly documented (Sochat et al., 2010). Little research has
been carried out yet into human appreciation of urban wildlife (Hofmann et al., 2012), but in general
it can be assumed that people do not appreciate animals damaging their property.
This is also the case with woodpeckers damaging facades of buildings in the Netherlands. In
the city of Utrecht, an apartment complex is being targeted by woodpeckers that damage the
facades by drilling holes in it. Even though the holes are being repaired, woodpeckers repeatedly
return to the house and damage another part of the facade. The holes are made at a height of
approximately 8 meters, therefore, a crane has to be used to reach the holes and repair them. As a
result, the costs of repairing the damage are high and have to be paid by the residents.
The problem of woodpeckers is not unique to this specific location, but it is quite new in the
Netherlands. During the writing of this thesis, two other locations were found where woodpeckers
damage facades of buildings. At these locations, similar traces of damage are found, but no practical
solutions are known yet. Moreover, no explanation can be given for the strange behavior of
woodpeckers drilling holes in facades of buildings. As a result, a challenge arises to find a satisfying
solution that incorporates both the preservation of biodiversity (woodpeckers) and solves the
conflict with urban residents. Moreover, an explanation has to be found for the unnatural behavior
of woodpeckers.
This ultimately leads to the research question for this thesis: “Why do woodpeckers damage facades
of buildings and how can the damage be mitigated?”
2
Outline
This thesis is a literature review on woodpeckers damaging buildings. Several hypothesis will be
discussed that might give an answer to the research question why woodpeckers damage facades of
buildings. Moreover, possible solutions to the problem will be discussed and the best solution that
can be used to mitigate damage by woodpeckers will be provided as recommendation. More
practical information and recommendations can be found in the accompanying practical report (Van
der Wal., 2013).
The first chapter of this thesis will elaborate on the general characteristics of woodpeckers,
woodpeckers’ behavior, legislation and the status of the woodpecker in the Netherlands. Thereafter,
benefits and adverse effects of woodpeckers will be discussed.
Adverse effects of woodpeckers will be discussed more thoroughly in the next chapter. The
problem of woodpeckers damaging buildings will be explained and several possible hypotheses will
be proposed that could explain the unnatural phenomenon.
In the third chapter possible solutions will be discussed that could mitigate woodpecker
damage to buildings. These solutions range from scaring woodpeckers to stop woodpeckers from
reaching the facades of buildings completely. Alternative food and nesting sources will be proposed,
as well as combining several different techniques.
In the final chapter a conclusion will be given based on the literature discussed in the
preceding chapters. Uncertainties will be explained and ideas for future practical research will be
provide. Based on this, recommendations for residents suffering from woodpecker damage and the
municipality of Utrecht will be given.
3
Chapter 1: Woodpeckers
Woodpeckers, family of the Picidae, can be found all around the world. The great spotted
woodpecker Dendrocopus major also lives in a wide array of areas, varying from arctic taiga to
temperate, alpine and Mediterranean forest zones (Cramp, 1985). In general it can be said that
wherever there are trees that can accommodate nest holes, the great spotted woodpecker can be
seen. As a result, the great spotted woodpeckers can be found throughout Europe and in large parts
of Russia, Japan and south-east Asia (Cramp, 1985). Besides their natural presence in forests,
woodpeckers are increasingly being spotted in city parks as well.
Woodpeckers are characterized by climbing, drilling, foraging and excavating cavities in trees.
Woodpeckers posses specialized beaks that can be used to excavate the outer layer of trees in search
for insects, beetles, nuts, berries or tree sap. The great spotted woodpecker specifically feeds on
wood boring insects, but often adds tree seeds and bird eggs and nestlings to his diet (Cramp, 1985).
Woodpeckers search for food in (partially) dead trees, since those are easier to penetrate
and harbor more insects. Trees are also used to excavate cavities for nesting and roosting. This manly
happens during breeding season that runs from the beginning of April till the end of June (Tupper,
2010). The great spotted woodpecker generally starts laying eggs during the last 10 days of April
(Mazgajski, 2002b). The initiation of the egg laying generally coincides with a higher temperature and
the resulting availability of food.
Territory display can be observed in the form of calls, drumming and fights from the
beginning of February till the start of the breeding season (Marsh, 1994). Outside the breeding
season woodpeckers sleep in roosting cavities, but they don’t actively excavate new ones (Marsh,
1994). Competition with other nest-hole users such as tits, nuthatch (Sitta europaea) and especially
starling (Sturnus vulgaris) is sometimes observed (Cramp, 1985).
1.1
Woodpecker status
In the Netherlands six different species of woodpeckers can be observed. Frequently seen
woodpecker species are the green woodpecker Picus viridis, lesser spotted woodpecker Dendrocopus
minor and the black woodpecker Drycopus martius (van Manen, 2002). One hardy sees the very rare
middle spotted woodpecker Dendrocopus medius and the Eurasian Wryneck Jynx torquilla (van
Manen, 2002).
By far the most common specie of woodpecker that can be observed in the Netherlands is
the great spotted woodpecker Dendrocopus major. The great spotted woodpecker is characterized
by a black and white plumage with red patches on the back of the head (male) and under the tail
(Fig. 1). The great spotted woodpecker can be found breeding almost everywhere in the Netherlands
(86% of the atlas blocks), but its presence generally coincides with tree density (van Manen, 2002).
The density of woodpeckers in older forests is observed to be higher than in younger forests, this is
probably because of the higher availability of dead wood in older forests (van Manen, 2002).
The great spotted woodpecker in the Netherlands is increasing every year. An estimated
62.000 great spotted woodpecker couples were found throughout the Netherlands in the period ‘98 ‘00, compared to 40.000 - 50.000 couples in the period ‘79 - ‘85 (van Manen, 2002). The same trend
is observed for the great spotted woodpecker in Britain and other countries in Europe as well (Smith,
2006). According to Birdlife International (2004), the great spotted woodpecker breeding population
is estimated to range between 12 and 18 million breeding pairs.
4
Figure 1: The great spotted woodpecker Dendrocopus major male (left) and female (right). (Photo’s:
Marek Szczepanek and www.bestemminginbeeld.nl).
1.2
Legislation
Woodpeckers in the Netherlands are protected by the Flora and Fauna law, which means that the
woodpeckers themselves are protected year round and their nesting cavities only during breeding
season. The objectives of the flora- and fauna law are to maintain the population of protected
species living in the wild. Actions that might disturb woodpeckers may therefore only be carried out
if woodpeckers are not being harmed. In practice this means that woodpeckers are not to be
disturbed during breeding season.
1.3
Drilling
Woodpeckers drill for several specific reasons, namely for drumming, foraging for food and for
excavating cavities (Germano & Vehrencamp, 2003). Woodpeckers are well known for hammering
loudly on old trees or other resonating surfaces such as stop signs, chimneys, gutters or metal down
spurts. Instead of singing, woodpeckers use drumming as a form of territory display and to attract
mates (Marsh, 1994). In general drumming does not result in large deep holes (normally with a
diameter smaller than 1 cm), it’s just about producing as much noise as possible (Marsh, 1994).
Research to woodpecker drumming showed any siding type can be a potential instrument for
woodpeckers, even non-wood facades (Harding et al., 2009).
Woodpeckers can be observed drilling as well when they are foraging for food. They prefer to
drill in dead trees in search for wood-boring insets or larvae. In general, foraging holes are not deep
and can be found in the form of horizontal rows on tree stems (Germano & Vehrencamp, 2003).
Woodpeckers also drill with the goal to excavating cavities that can be used for nesting or
roosting (Germano & Vehrencamp, 2003). Cavities of great spotted woodpecker are characterized by
round openings (diameter 5 - 6 centimeter) that lead to 25 - 35 cm deep holes (Cramp, 1985). Great
spotted woodpecker uses old nesting holes for roosting all year round, but excavating new holes just
for roosting rarely occurs (Mazgajski, 2002a). Research to different characteristics of woodpecker
cavities showed no differences in cavities used for roosting or for nesting (Mazgajski, 2002b).
Because of higher predation risk and the presence of overwintering ecto-parasites in old
nesting sites, woodpeckers generally excavate new cavities for nesting every year (Mazgajski, 2007).
It is also suggested that woodpeckers protect their offspring against predators by making nest holes
in trees without old cavities. This idea is supported by research that showed that the great spotted
woodpecker mainly excavated holes for nesting in trees without older holes (Mazgajski, 1998). A lack
of suitable nesting trees however might force woodpeckers to use old nesting cavities.
5
1.4
Nesting trees
A well known mistake is that woodpeckers mainly use dead trees for roosting and nesting, but
research showed that 85% of nesting and roosting holes are made in living trees (Mazgajski, 2002b).
Great spotted woodpeckers mainly use oaks Quercus sp., birch Betula verrucosa, aspen Populus
tremula and Ashes Fraxinus excelsior for nesting (Mazgajski, 2002b; Kosinski, 2007). They can
sometimes also be found in pine Pinus silvestris, grey alder Alnus incana and linden Tilia cordata as
well. However, this preference for tree species is observed in mixed deciduous forest and could be
different when trees are available in different ratios.
When woodpeckers excavate cavities they first drill horizontally through the hard sapwood
(outer layer) and thereafter they excavate a vertical cavity in the core of the tree (Fig. 2). Research to
wood hardness of trees showed that the depth of the vertical drilled cavities was negatively
correlated with the hardness of the core wood (Matsuoka, 2008). This suggests that woodpeckers do
not necessarily prefer trees of a certain species or with a specific diameter or height, but instead they
select on the hardness of the core (Matsuoka, 2008). Other research showed that woodpeckers are
capable of detecting characteristics that determine wood hardness, because woodpeckers chose nest
trees that were softer than neighboring or random trees (Schepps et al., 1999).
This is supported by the fact that woodpeckers prefer to nest in trees that are infected by
fungi that causes the core to soften and develop a so called heart wood rot (Jackson and Jackson,
2004). This is confirmed by studies that showed that Aspen Populus tremula were very both popular
trees for nesting and susceptible to heart wood rot as well (Aitken et al., 2002). Woodpeckers
probably prefer trees with heart rot because it requires less time and energy to excavate the cavity
(Newton, 1994). Moreover, the strong outer sapwood still protects them against predators and
prevents the tree from falling over during strong winds (Jackson and Jackson, 2004).
Figure 2: Illustration of a cavity drilled by a woodpecker (left) and different heights at which wood
hardness was measured at a nest tree (right; Matsuoka, 2008).
1.5
Positive impact of woodpeckers on ecosystems
Woodpeckers drill holes in order excavate cavities for themselves and are therefore termed primary
cavity nesters. Woodpeckers typically abandon their nest after one season and leave their holes
unused (Matsuoka, 2008). Other so called secondary-cavity birds do not posses specialized beaks to
drill their own holes and do therefore depend on woodpeckers to do the heavy work for them.
Moreover, small mammals such as raccoons and pine martens also benefit from the work of
woodpeckers. As a result, woodpeckers are often referred to as key stone species because they serve
an important role in maintaining biological diversity of other cavity users in forest ecosystems
(Newton, 1994). In Europe, the majority of the holes of secondary cavity nesters are provided by the
6
great spotted woodpecker Dendrocopus major and the black woodpecker Drycopus martius (Virkkala,
2006).
Another positive impact of woodpeckers comes from the fact that they eat insects. Research
showed that woodpeckers can prevent or slow down local outbreaks of insect pests (Jasumback et
al., 1999). They also protect valuable timber resources by eating insects harmful to trees (Conner and
Crawford, 1974) and help farmers controlling insect pests such as grasshoppers or beetles
(Jasumback et al., 1999).
1.6
Negative impact of woodpeckers on humans
Unfortunately, the presence of woodpeckers can sometimes cause problems as well. Woodpeckers
living in rural areas are sometimes observed to cause damage to, buildings, trees and utility poles.
Research used to focus on damage on utility poles, since it created significant economic impacts on
electrical service companies and their consumers (Stemmerman, 1988).
The most expensive example of woodpecker damage was in 1995 to Space Shuttle Discovery.
At least 135 holes were drilled in the foam insulation of the fuel tank of the spacecraft and as a result
it had to be rolled back to the assembly building (Fig. 3). Even though it only happened once, this
action delayed the launch of the space shuttle with several weeks and was estimated to costs around
1 million dollar.
Woodpeckers have also been observed to drill holes in polyethylene pipes that were used for
irrigation in Orchards in Israel (Wolf, 1973). As a result a lot of valuable water was lost and a lot of
time and money was spent to repair the damage.
Damage by woodpeckers drilling holes in facades and window frames of houses was even
more extensive. It resulted in an average repair costs around 300 dollar per case and annually in the
US woodpeckers are estimated to cause millions of dollars of damage (Craven, 1984). As a result
extensive research has been carried out on woodpecker behavior in order to find solutions to
prevent damage to buildings.
Recently woodpeckers have been observed to damage buildings in the Netherlands as well.
On two separate locations, buildings in the city of Utrecht were targeted by the great spotted
woodpecker Dendrocopus major. At both locations woodpeckers excavated several different cavities
in the soft plaster facades of the building. Even after repairing the cavities, woodpeckers kept on
coming back to drill more holes or to reopen old ones. No research on woodpeckers damaging
buildings in the Netherlands has been carried out yet; therefore this problem poses an interesting
challenge. Research will focus on the great spotted woodpecker only, because in all cases it was the
woodpecker species observed to be responsible for the damage to buildings in the Netherlands (Van
der Wal, 2013).
Figure 3: A woodpecker drilled several holes in the hydrogen storage tank of the space shuttle at Cape
Carneval, Florida, USA. (Photo: www.nasa.gov)
7
Chapter 2: Woodpeckers damaging buildings
Woodpeckers damaging facades of buildings is a well known problem in the US, but it is not much
heard off in the Netherlands. As mentioned in the previous chapter, the great spotted woodpecker
Dendrocopus major has been observed excavating cavities in the facades of several buildings on
separate locations in the city of Utrecht (Fig. 4). Utrecht is the 4th city of the Netherlands and is home
to 321.583 inhabitants (CBS, 1 Nov. 2012). Woodpeckers damaging buildings have been reported in
the city Katwijk as well, but up to now the magnitude of the problem in the Netherlands still is not
clear.
Figure 4: Cavities excavated in the facade of a building in Utrecht by the great spotted woodpecker
Dendrocopus major. (Photo: Stefan van der Wal)
Moreover, no research has been carried out yet on woodpeckers damaging buildings in the
Netherlands, therefore literature from research abroad has to be used. Research on woodpecker
damage on buildings in the US has been carried out, but those buildings were often constructed of
wood and are therefore likely targets for woodpeckers (Harding et al., 2007; Harding et al., 2009).
The problem in the Netherlands seems comparable, because facades of buildings that are damaged
by woodpeckers are made of plaster material that can be easily penetrated by woodpeckers as well.
However, even in the US researchers still do not know the exact reason why woodpeckers
damage buildings. As mentioned earlier, woodpeckers might inflict structural damage on the facades
of buildings in search for food, during drumming activities or to excavate nesting cavities.
Several different hypotheses will be addressed in this chapter that might explain why woodpeckers
are damaging buildings:

Woodpecker might damage buildings in search for food.

Hollow facades may resemble the sound of dead trees.

Buildings might suffer from woodpecker damage, because they are located near forests,
parks or green areas with a lot of trees.

Buildings that suffer from woodpecker damage are made of a specific material that
attracts woodpeckers or is too soft and therefore easy to penetrate.

Woodpeckers might be attracted by the color of the facade of the house.

Heat from the house might provide a better internal climate for roosting / nesting holes.

A shortage of suitable trees that can be used for nesting might result in woodpeckers
excavating roosting / nesting cavities in buildings.

Inter- or intra specific competition for nesting sites with secondary cavity users might
result in woodpeckers excavating roosting / nesting cavities in buildings.
8
2.1
Foraging or drumming
Research in the US showed that insects crawl into small holes in facades of buildings to overwinter,
pupate or hide from predators (Germano & Vehrencamp, 2003). It is suggested that woodpeckers
might therefore drill holes in facades of buildings in search for food. Traces of foraging activities can
be detected as horizontal rows of small holes (with a diameter of 1 - 3 cm) around the stem, branch
or on the facade of a house (Harding et al., 2009).
It is also suggested that the sound of pecking on (hollow) facades of buildings may resemble
the sound of dead trees. Woodpeckers normally perform foraging or drumming activities on dead
trees. Drumming activities are performed on hollow surfaces in order to demarcate their territory or
to attract potential mates (Marsh, 1994).
2.2
Tree density
Research in the US showed that tree density in the area around a building has an effect on the
chance that woodpeckers damage a building (Harding et al., 2009). A linear increase was observed in
the probability of woodpecker damage to a house, when the abundance of trees increased (Harding
et al., 2009; Fig. 5). This makes sense, since the presence of trees coincides with the availability of
food for woodpeckers. In addition, woodpeckers may feel more protected against predators when
more trees are around. Therefore it is suggested that houses in the vicinity of parks, forests or green
areas suffer more from woodpecker damage.
Figure 5: Proportion of houses with woodpecker damage compared to different yard types. For yard type:
HW = heavily wooded, W = wooded, LW = lightly wooded, OG = open grassy (Harding et al., 2009).
2.3
Building characteristics
Research showed that woodpecker damage also depends on the material the facades of a building
are made of. Research has shown that cedar, multiplex and tong-grove wood types are targeted
more often than other types of wood (Harding et al., 2009). In the Netherlands polystyrene is
sometimes used in the construction of buildings. The composition of polystyrene is comparable to
wood tissue and can by woodpeckers be seen as possible nesting site (Conner, 1996). Both
polystyrene and decayed wood can be drilled open pretty easy and are therefore likely targets of
woodpeckers. This could be explained by the fact that excavating cavities takes a lot of energy
(Newton, 1994). As mentioned earlier, woodpeckers prefer trees that suffer from heart rot, since it is
easier to excavate a large cavity in softer core wood (Jasumback et al., 1999). This is supported by the
fact that non-wood houses in the US received significantly less damage than wooden houses (Harding
et al., 2009).
9
Other research to characteristics of houses prone to woodpecker damage in the USA, showed that
color is important for woodpeckers. Research showed that houses with earth colored facades
experienced significantly more woodpecker damage than the ones painted with bright pastel colors
or white (Fig. 6; Harding et al., 2007). This may be explained by the fact that earth-colored paint
resembles the color the trees that woodpeckers normally excavate.
Figure 6: Proportion of houses with woodpecker damage in relation to facade color. Gray bars show the
uncorrected proportion of homes with woodpecker damage, white bars represent least-squares mean
proportion and standard error after correcting for house siding and yard types. Numbers in the white bars
represent the total number of houses examined (Harding et al., 2007).
It is also suggested that woodpeckers might be attracted to buildings, because of the smell or taste of
the material the facades are made off. Research has shown that both smell and taste do not work as
a repellent, because woodpeckers do not ingest the material (Belant et al., 1997). However, this does
not exclude that woodpeckers might still be attracted by the smell or taste of a certain material that
might be processed in the wood or plaster.
Another hypothesis suggests that the heat that escapes from the house might attract
woodpeckers. Cavities in facades would be more comfortable than natural cavities and protect
woodpeckers against the cold weather. It is known that weather and wind direction might result in
woodpecker migrating to warmer roosting holes (Mazgajski, 2002a). Moreover, several species of
bats are observed to use cavity walls in houses as well because of the favorable temperature.
2.4
Competition on nesting sites
Another hypothesis suggests that woodpeckers might damage facades of buildings, because there
are no or insufficient suitable nesting trees available. As a result, woodpeckers would excavate
nesting cavities in facades of buildings. The shortage of suitable nesting trees could be a result of
urban development towards woodpecker ecosystems that has degraded woodpecker’s habitat (Linn,
1982). Park management could also have an effect on the availability of suitable nesting trees.
Damaged, sick and dead trees are sometimes removed from city parks because they pose a potential
threat for visitors. The removal of these trees may result in insufficient suitable nesting trees for
woodpeckers. Moreover, the tree composition in urban parks may be too young to contain trees that
are suitable for woodpeckers for nesting (Newton, 1994).
10
2.5
Competition for nesting sites
Another hypothesis suggests that competition for nesting sites with other (secondary) cavity nesters
might result in woodpeckers excavate cavities in houses. As mentioned before, woodpeckers
typically leave their nests abandoned after one season (Matsuoka, 2008). So called secondary cavity
nesting birds take over these abandoned woodpecker holes to raise their own offspring. However, in
managed forests or city parks, suitable nesting trees may be scarce and as a result woodpeckers
might want to use their old cavities as well (Kotaka & Matsuoka, 2002). As a result, competition
between woodpeckers and secondary cavity nesters might arise.
Moreover, the growing population of great spotted woodpeckers Dendrocopus major in the
past few decades in the Netherlands might result in inter-specific competition as well (van Manen,
2002). As a result of the competition for potential nesting sites, woodpeckers might drill new nesting
cavities in facades buildings.
2.5.1 Competition for nesting sites with the ring neck parakeet Psittacula krameri
It is suggested that ring neck parakeets Psittacula krameri might compete with great spotted
woodpeckers on potential nesting sites (Strubbe & Matthijsen, 2007). The ring neck parakeet is an
exotic bird that comes from Africa and South-east Asia. Ring neck parakeets probably escaped or
were set free from an aviary and seemed to do quite well in the parks of big cities in de the
Netherlands. The number of ring neck parakeets in the Netherlands is growing dramatically. Between
2004 and 2010 the number of ring neck parakeets doubled from 5.000 to almost 10.000 counts
(Klaassen and Hustings, 2010).
Research to the effects of ring neck parakeets on other cavity nesters in Brussels, Belgium,
showed a negative association between the presence of ring neck parakeets and the nuthatch Sitta
europaea (Strubbe & Matthysen, 2007). Competition between ring neck parakeets and other cavity
nesters was experimentally tested by blocking the entrances of ring neck parakeet’s nests (Strubbe &
Matthysen, 2009). This resulted in parakeets taking over holes of the nuthatch in the area and a
significant lowering of the nuthatch population (Strubbe & Matthysen, 2009). Nuthatch and ring neck
parakeets both make use of old woodpecker holes and thus overlap in preferred nest sites
(Matthysen, 1998; Butler, 2003). This leads to competition between the two species and results in a
reduction in nuthatch numbers, when suitable nest sites become scarce (Strubbe & Matthysen,
2009). No direct aggression between the two species has been observed, but the competition can be
explained by the fact that parakeets start laying eggs already at the end of February (Butler, 2003),
while nuthatches start breeding only in the second half of April (Matthysen, 1998).
Competition between ring neck parakeets and great spotted woodpeckers was not observed
on population level (Strubbe & Matthysen, 2007), but that doesn’t rule out competition entirely.
Competition would probably not be visible on population level, because woodpeckers are able to
excavate their own cavities (Kotaka & Matsuoka, 2002). However, the competition between the two
species could occur and result in woodpeckers drilling holes in facades of nearby buildings.
2.5.2 Competition for nesting sites with European starling Sturnus vulgaris
Another secondary cavity nester that might compete with the great spotted woodpecker on nesting
sites is the European starling Sturnus vulgaris. Research showed that the introduction of European
starlings in New York resulted in a significant change in population density of several cavity-nesting
species (Koenig, 2003). However, no effects on the population of the occupant woodpecker species
were detected (Koenig, 2003).
Research to secondary cavity nesters in urban environments in Japan showed that starlings
are the main secondary cavity nesters that use cavities drilled by great spotted woodpeckers
Dendrocopus major (Kotaka & Matsuoka, 2002). This is probably because starlings are the dominant
species in competition for cavities. The presence of starlings also affected woodpeckers, because a
lower reuse rate of old cavities by the great spotted woodpecker was observed when starlings were
present (Mazgajski, 2000).
11
Intra-specific competition on the available suitable nest trees between woodpeckers and the
European Starling Sturnus vulgaris was also observed to be strong in British Colombia (Aitken et al.,
2002). Starlings sometimes even took over newly excavated cavities and as a result woodpeckers had
to reuse existing cavities or excavate new ones (Aitken et al., 2002). The same was observed in Japan,
where starlings were observed to usurped cavities of five cavities that were just excavated by great
spotted woodpecker pairs (Kotaka & Matsuoka, 2002; Cramp, 1985). The effects of competition
between starlings and woodpeckers may not be visible on population level, because some
woodpecker pairs were able to build a second nest later in the season (Kotaka & Matsuoka, 2002).
Intra-specific competition might however be responsible for the fact that woodpeckers have to find
new nesting sites and as a result drill holes in facades of buildings.
The hypothesis of intra-specific competition on nest sites between starlings and the great
spotted woodpecker is also supported by a long term study (20 years) in Britain (Smith, 2005). In the
early years of the study, great spotted woodpecker’s nest site interference by starlings was
frequently observed and probably responsible for the nest failure or delayed breeding of the great
spotted woodpecker (Smith, 2005). The decline and ultimately disappearance of starlings from the
study area later on in the study period, may have contributed to the increase in the great spotted
woodpecker population (Smith, 2006). From these observations it might be concluded that
competition between starlings and woodpeckers does occur and that this competition has a negative
effect on woodpecker populations.
12
Chapter 3: Mitigating woodpecker damage
Several techniques have been proposed to prevent woodpeckers from damaging facades of buildings
(Harding et al., 2007). These techniques focus mainly on scaring woodpeckers or providing them with
alternative food- or nesting sources. Moreover, the targeted buildings could be reinforced in order to
stop woodpeckers from reaching or damaging the outer wall of the building. Maybe the most
effective solution is a combination of different techniques and careful construction planning of
buildings near parks or in forest areas in the future. In that way, current damage might be mitigated
and future damage to buildings by woodpeckers may be prevented.
3.1
Woodpecker damage
Damage to facades of buildings by woodpeckers could be a result from foraging- or drumming
behavior or from the fact that woodpeckers need to excavating holes for nesting. The type of
damage inflicted by woodpeckers has to be determined before an appropriate technique is chosen to
mitigate damage to facades.
If rows of small holes are detected in the facades of a building (Fig. 7), it indicates
woodpecker’s foraging behavior on insects or larvae (Germano & Vehrencamp, 2003). Woodpecker’s
drumming behavior mostly results in a lot of noise, but doesn’t cause extensive damage (Marsh,
1994). Traces from drumming activities can sometimes be found as holes in the form of dents that
are grouped in clusters. Woodpeckers also excavate cavities that can be used for nesting or roosting
(Germano & Vehrencamp, 2003). These cavities can be observed as large round holes in the outer
wall of a building (Fig. 8).
Figure 7: Woodpecker foraging holes in vertically grooved plywood (Photo: Cornell lab of ornithology)
Figure 8: woodpecker nesting / roosting holes in cedar clapboards (Photo: The Cornell lab of ornithology).
3.2
Scaring techniques
If a woodpecker is seen drilling on the facade of a building, it may be scared away immediately by
making loud noises or throwing water at the woodpecker. These methods do however need
permanent supervision; therefore devices that frighten woodpeckers and can be left in place are
designed as well. Examples of such devices are models of prowler owls or birds of prey that can be
manufactured and mounted on poles in order to frighten woodpeckers (Fig. 9; Harding et al., 2007).
This method has one huge disadvantage that woodpeckers get accustomed to a visual stimulus that
13
comes from the same place every day. Therefore in order to be effective, the model of an owl or bird
of prey has to be relocated to a different location every few days.
A similar method that can be used to shoo woodpeckers is based on sounds woodpeckers
and potential predators produce. This so called Bird-Pro sound system produces distress calls of
woodpeckers followed by the call of a predator (Harding et al., 2007). This sound system doesn’t
have to be relocated every few days, but the purchase costs are relatively high.
Less expensive ways of scaring woodpeckers are available as well. Bright yellow and orange
holographic eyes made of plastic can be hung on a fishing line on the side of a building as well. These
so called scare-eyes resembling a predator and may therefore be effective in fighting woodpeckers
of. Another relatively cheap method to scare woodpeckers is the use of reflective ribbon that can be
hung on the sides of a building. This so called Irri-tape is a silver reflective ribbon that can be hung on
a string so that it can rattle in the wind and reflect the light of the sun (Harding et al., 2007).
Every of the mentioned techniques to scare woodpeckers showed a reduction in woodpecker
damage at some homes. However, the use of irri-tape definitely showed the highest improvement,
because at 5 out of 10 trails woodpeckers didn’t return to the house after installing the deterrent
(Harding et al., 2007). Prowler owls and the bird-pro systems showed much lower improvement rates
(1 out of 6) and at some houses even resulted in an increase in damage rate after the installation of
the deterrent (Harding et al., 2007).
Figure 9: Prowler owl tested as woodpecker deterrent (Harding et al., 2007).
Another method to mitigate dame done to facades of buildings is to scare woodpeckers by using
chemical repellents. Methyl-anthranilate is such a bird repellant that was experimentally tested to
scare woodpeckers in the USA (Belant et al., 1997). In this experiment, methyl anthranilate was both
mixed with food in suet feeders and applied on wooden facades of buildings that are damaged by
woodpeckers. Woodpeckers were successfully repelled from suet feeders after ingesting the methyl
anthranilate, but no effect was observed at facades of buildings. Researchers concluded that
chemical repellents in general would be ineffective in reducing woodpecker damage to buildings,
because woodpeckers do not ingest the wood when drilling (Belant et al., 1997). This is confirmed by
experiments with chemical repellants on European starlings Sturnus vulgaris that only proved to be
successful, when the repellant was ingested (Sayre and Clark, 2001).
3.3
Alternative food source
As mentioned earlier, woodpeckers might damage facades of buildings in search for food. Insects
crawl into small holes to overwinter, pupate or hide from predators and form a perfect food source
for woodpeckers (Germano & Vehrencamp, 2003). If foraging damage is observed, pest control
companies should be contacted in order to eliminate the insects that attract woodpeckers.
14
Moreover, it is suggested that suet feeders might be placed nearby to provide woodpeckers with an
alternative food source and keep them away from the houses (Harding et al., 2007). However,
experiments with suet feeders near houses prone to woodpecker foraging damage, showed no
significant decrease in damage rate (Harding et al., 2007). At some houses the damage rate even
increased after placing suet feeders. This might be explained by the fact that suet feeders could also
attract more woodpeckers to the area.
3.4
Alternative nesting sites
If no suitable trees are around to excavate a nesting cavity, woodpeckers might use facades of
buildings instead. This problem might be solved by providing woodpeckers with alternative nesting
sites nearby (Jasumback et al., 1999). Since woodpeckers prefer to drill in trees that suffer from heart
rot, old trees are most suitable for this method. A long term solution could be found by pointing out
so called ‘wildlife trees’ that may be used by woodpeckers and other cavity nesters (Jasumback et al.,
1999). These old large trees could be topped and let to die slowly. The additional benefit of this
method is that a topped tree won’t be a safety risk for visitors or people living nearby. Girdling of the
base of a tree is not recommended, because these trees will fall over quickly and won’t be of use to
woodpeckers anymore (Jasumback et al., 1999).
In the case of urban forests or parks it may not be possible to top trees. Therefore, dead
trees can be placed in the park to provide woodpeckers with extra nesting possibilities. Experiments
with artificial polystyrene trees in the USA, showed that some downy woodpeckers Picoides
pubescens excavated holes in the artificial snags (Conner and Saenz, 1996). Although no
woodpeckers were observed to nest in any of these objects, they regularly used the cavities for
roosting (Conner and Saenz, 1996). This might result from the fact that the quality of the artificial
trees is inferior to normal trees. Moreover, the investigated areas had a surplus of trees suitable for
nesting; therefore artificial trees were probably unattractive to woodpeckers (Conner et al., 1994).
Roost boxes designed for woodpeckers could be used as well to provide woodpeckers with
extra nesting locations. An advantage of woodpeckers nesting in artificial trees or nest boxes is that
they will defend their territory en therefore keep other woodpeckers away that could potentially
damage the facades of a building (Andelt et al., 2012). Research in the USA showed that the
installation of cavity-type nest boxes reduced damage to facades, but it couldn’t entirely rule it out
(Marsh et al., 1990). It was suggested that woodpeckers feel the urge to excavate their own cavities
as part of the breeding ritual. Filling the nest boxes with saw dust might therefore fool the
woodpeckers and let them think that they are constructing their own nest (Marsh et al., 1990).
3.5
Home characteristics
Apart from scaring woodpeckers or providing woodpeckers with alternative nesting sites, facades of
buildings prone to woodpecker damage could be made less attractive as well. Research showed that
houses with brown or earth color facades received much more damage from woodpecker than the
ones that were painted with bright pastel colors or white (Harding et al., 2007). Therefore it might
help to alter the color of the facade of a building to bright pastel or white.
3.6
Excluding woodpeckers
If other methods fail to mitigate damage to facades, woodpeckers could be prevented from reaching
the façade entirely. This could be done by installing chicken wire, aviary mesh or plastic netting a few
centimeters away from the wall (Belant, 1997; Jasumbach et al., 2000). Moreover, the facade of the
building could be covered completely with vinyl or aluminum (Harding et al., 2007). These methods
do however have huge disadvantages, because they are expensive and make the building look quite
unsightly.
3.7
Lethal control
All woodpecker species in the Netherlands are year round protected by the Flora- en Fauna law, so
lethal control on woodpeckers damaging facades of buildings is not an option.
15
Chapter 4: Discussion
Several hypotheses have been proposed to answer the research question “why do woodpeckers
damage facades of buildings and how can the damage be mitigated?” First, these hypotheses are
discussed in the main findings that may apply to the problem in the Netherlands. Uncertainties are
discussed next. Subsequently, recommendations are given that might be implemented to mitigate
damage to buildings by woodpeckers. Last, suggestions for future research are provided.
4.1
Main findings
First of all it is suggested that the number of trees surrounding the building targeted by woodpeckers
could contribute to the unnatural behavior of woodpeckers. Research showed that tree density
around the building influenced woodpecker damage and the chance of damage linearl increased with
the abundance of trees in the yard (Harding et al., 2009). This seems a plausible explanation, since
the buildings in the Netherlands that are known to be targeted by woodpeckers are located near the
parks or wooden areas.
Besides the location, it is also suggested that the material that the houses are made of may
contribute to the problem of woodpeckers damaging buildings. Research in the US showed that color
matters, because brown and earth colored houses were targeted more often by woodpeckers, than
white or pastel colored ones (Fig. 4; Harding et al., 2007). Moreover, it is argued that softer materials
have a higher chance of being targeted by woodpeckers (Harding et al., 2009). This is most likely
because excavating cavities in softer material requires less energy (Jasumback et al., 2009). This
hypothesis seems plausible for buildings in the Netherlands that suffer from woodpecker damage,
because they are made of polystyrene plates covered with a layer of plaster. Research into artificial
nesting sites for woodpeckers in the US used polystyrene, because the material was almost identical
to the structure of dead wood (Conner, 1996). Moreover, plaster is an extremely soft material that
can be easily penetrated by woodpeckers.
It is proposed that woodpeckers might damage facades of buildings, because there are no or
insufficient suitable nesting trees available. As a result of this shortage of suitable nesting trees,
woodpeckers might excavate nesting cavities in facades of buildings. The lack of suitable nesting
trees could be a result of the fact that the tree composition in urban parks is too young (Newton,
1994). Moreover, the removal of damaged, sick and dead trees by park managers may result in
insufficient suitable nesting trees for woodpeckers.
Researchers argue that competition between woodpeckers and secondary cavity nesters on
available nesting holes might occur (e.g. Aitken et al., 2002). Especially when this competition takes
place in an area with a shortage of suitable trees that can be used by woodpeckers for excavating
cavities. As a result of competition and a shortage of suitable nesting trees, woodpeckers might
excavate nesting cavities in facades of buildings. Two possible secondary cavity nesting species that
might compete with woodpeckers on available cavities would be the ring neck parakeet Psittacula
krameri and the European starling Sturnus vulgaris. In forests there probably wouldn’t be a shortage
of suitable nesting trees, but in managed city parks this hypothesis would be plausible (Newton,
1994). This is supported by observations of European starlings occupying great spotted woodpecker
cavities more frequently in urban than in suburban forests (Kotaka & Matsuoka, 2002).
Moreover, not only the number of cavities, but also the quality of the available cavities might
influence competition for nesting sites between different species (Lohmus and Remm, 2005).
Especially since older cavities are generally considered of lower quality by cavity nesters, the newly
excavated cavities are definitely favored. Moreover, research has shown that different cavities in the
same tree cannot be occupied simultaneously by cavity nesters (Lohmus and Remm, 2005). As a
result, competition with other secondary cavity users might force woodpeckers to look for new or
higher quality nesting locations. As a result, woodpeckers could damage facades of buildings and use
them to excavate cavities.
16
4.2
Uncertainties
One of the main concerns regarding the literature used for underpinning the hypotheses and
practical solutions is that all research was carried out abroad. Research in several occasions focused
on different woodpecker species or was carried out in different environments. Besides, wood is more
often used in the construction of buildings in the US, while this is rather uncommon in the
Netherlands. This should be taken into account when hypothesis and practical solutions are
discussed. Therefore, preliminary and experimental research should be carried in the Netherlands
first, before firm conclusions can be drawn.
4.3
Recommendations
Several solutions are suggested to mitigate woodpecker damage to facades of buildings. Research
showed that the use of reflective ribbons that can be hung on the side of a building are the most
effective method to scare woodpeckers (Harding et al., 2007). In addition, reflective ribbons are an
inexpensive and easy method to implement. Unfortunately, it didn’t solve the problem completely,
because after installing the deterrent, woodpeckers did only not return in 50% of the cases (Harding
et al., 2007).
Moreover it is suggested to repair damage to facades of buildings right away, to prevent
woodpeckers from getting accustomed to living at the specific location (Mazgajski, 2002b) or to
prevent attracting even more woodpeckers (Harding et al., 2007). To prevent woodpeckers from
reopening repaired holes, it is suggested to repair damage to facades with very strong materials (e.g.
Epoxy; Stemmerman, 1998). Moreover, it is suggested to use white or pastel colored materials to
repair the damage (Harding et al., 2007).
If a shortage of suitable nesting trees is an issue, it is suggested to provide woodpeckers with
alternative artificial nesting sites nearby (Jasumback et al., 1999). This could be done by placing nest
boxes designed for woodpeckers. Researched showed this method somewhat reduced damage to
facades, but couldn’t rule out damage to facades completely (Marsh et al., 1990). Moreover,
additional nesting sites could be provided by topping some trees and let them die slowly. These trees
could be appointed as ‘woodpecker trees’ and may be used by woodpeckers and other cavity nesters
(Jasumback et al., 1999). If it is not possible to top trees, dead trees can be placed in the park to
provide woodpeckers with extra nesting possibilities. Experiments with artificial polystyrene trees in
the USA, showed that some downy woodpeckers Picoides pubescens excavated holes in the artificial
snags (Conner and Saenz, 1996). Although no woodpeckers were observed to nest in any of these
objects, they regularly used the cavities for roosting (Conner and Saenz, 1996).
If none of these solutions work out it can be considered to exclude woodpeckers from
reaching the outer wall. This could be done by installing chicken wire, aviary mesh or plastic netting a
few centimeters away from the wall (Belant, 1997; Jasumbach et al., 2000) or even to cover the outer
wall completely with vinyl or aluminum siding (Harding et al., 2007). An overall solution however,
might be found in a combination of different techniques. Irri-tape should be used initially to scare the
woodpeckers away. In addition, extra nesting capacity could be created by installing nest boxes or
placing dead trees in the nearby area.
Because of the highly dynamic nature of urban ecosystems a small effort in management can
have a great effect on bird abundance and diversity (Savard, 2000). It is shown that woodpeckers
serve a very important role in maintaining biological diversity of cavity users in forest ecosystems
(Newton, 1994). Therefore, it is suggested that city and park managers protect trees that are used by
woodpeckers. Especially old, damaged and dead trees are important for creating and maintaining a
sustainable breeding habitat for woodpeckers.
17
4.4
Recommendations for future construction
In order to prevent woodpeckers from damaging buildings in the future, it could be considered to
adjust the way in which buildings are constructed near parks, forests or wooden areas. It is suggested
that buildings near parks in the future shouldn’t be constructed with materials that can be damaged
easily by woodpeckers. Moreover, facades of buildings shouldn’t be painted with brown or earth
colored colors. Instead, stronger material like bricks, concrete or other non-wood material that is
more resistant to woodpecker damage should be used and facades should be painted with white,
light blue or pastel colors (Harding et al., 2007). This new way of building houses in woodpecker
sensitive areas should be communicated to developers, builders, city planners and house owners.
Especially, since it is much better to prevent woodpecker damage beforehand instead of
continuously repairing the damage.
4.5
Future research
In order to verify the suggested hypothesis, future research should be carried out in areas where
buildings are being damaged by woodpeckers. Research could focus on the two known locations in
Utrecht, where woodpeckers damage facades of buildings. Research should first of all focus on the
exact type of woodpecker behavior that is responsible for the damage to facades. This could be done
by observing facades of buildings that are damaged by woodpeckers. Next, available data of
population changes of primary- and secondary cavity nesters over the past years should be analyzed
in order to support the hypothesis of competition with secondary cavity nesters on available cavities.
Next, possible trends could be related to events such as changes in park management and the onset
of the damage to damage buildings by woodpeckers.
Moreover, the condition of the trees surrounding the two locations should be analyzed in
order to get a better understanding of the availability of trees that are suitable for woodpeckers for
excavating cavities. This could be combined with extensive fieldwork in order to get a better view on
the number of woodpeckers, secondary cavity nesters and suitable trees for nesting. In the end this
research would contribute to a better understanding of the potential mechanisms at the two
locations and could serve as reliable basis for giving recommendations and providing practical
solutions.
In regard to methods to prevent woodpeckers from damaging facades of buildings, extensive
research is necessary as well. The deterrents mentioned in this thesis have only been tested at a few
locations in the USA, therefore future research should focus on repeating experiments with scaring
devices in the Netherlands. Moreover, it is recommended that research focuses on combining
different methods in order to achieve a higher success rate. It is especially recommended to combine
the method of installing irri-tape and provide woodpeckers with extra nesting capacity.
Further research on artificial nesting sites should be carried out as well in areas with a
shortage of suitable trees for nesting. This research should also be aimed at finding out what kind of
material or type of nest box is preferred by woodpeckers.
Moreover, experiments can be carried out, where large trees that are redundant elsewhere,
are transported to a location where woodpeckers damage buildings. These trees should be chopped,
topped, placed in the ground and infected with decay fungus in order to enhance heart rot. This
method will definitely not be a cheap solution, especially because heavy machinery has to be used
for placing and transporting the tree. However, if nearby trees have to be removed anyway as a
result of the construction of a road for example; this solution should be feasible without spending
extraordinary amounts of money.
18
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