A Survey of Rusty Blackbird Populations in
Northeastern Vermont
Research into habitat, distribution and breeding biology
A Senior Applied Research Project by Caleb Fisher
Sterling College, 2007
Life History and Status of the Rusty Blackbird
The Rusty Blackbird, Euphagus carolinus, is the northernmost breeder of the Icteridae, or North
American blackbirds. This species, dependent on forested wetlands in both the breeding and
non-breeding seasons, winters in the southeastern United States and breeds in boreal areas of
North America. Unlike most other Icterids, whose populations remain healthy, the Rusty
Blackbird has experienced massive population declines in the past century. While many theories
exist for the causes of decline, there is an evident lack of both data and monitoring programs to
support any of these theories and to provide a fully accurate assessment of their current
population. The lack of attention given to Rusty Blackbirds has caused their decline to be largely
overlooked by bird researchers, conservationists and the general public (Greenberg and Droege,
1999).
Physiological Characteristics
Rusty Blackbirds, named after their non-breeding plumage, are recognized in the fall and winter
by overall black plumage and rusty brown coloring on the crown, nape, back and tertial edges of
the males with a lighter brown over the eyes, cheeks, throat and breast (Avery, 1995). Females
are similar in appearance but have lighter, buff-brown edgings on their eyes, cheeks, throat, sides
and breast, as well as a pale buff line above the eyes. In the breeding season, males are
uniformly black with a blue-green to green gloss while females are slate gray, darker above, with
a blue-green gloss. Immature birds are overall more brown appearance and have brown irises
until the fall. All mature Rusty Blackbirds have a yellow iris and a bill that is shorter than the
head. The two species most easily confused with Rusty Blackbirds are the Brewer’s Blackbird
(Euphagus cyanocephulus) and the Common Grackle (Quiscalus quiscula) (Avery, 1995).
Taxonomy
Rusty Blackbirds belong to the Passeriformes order and the Icteridae, or the New World
blackbird, family. This family contains 94 species and is thought to have evolved from a finchlike ancestor in tropical South America (Orians, 1985). The closest relative of the Rusty
Blackbird is the Brewer’s Blackbird (Euphagus cyanocephalus) with Euphagus appearing most
closely allied with the grackles (Quiscalus) (Irwin, 1994, Hannah, 2004). Rusty Blackbirds are
divided into two subspecies: Euphagus carolinus carolinus, distributed over most of the species
range and the darker E. c. nigrans, breeding in Nova Scotia, Newfoundland, Magdelan Island and
eastern New Brunswick (Avery, 1995, Hannah, 2004).
Distribution
Rusty Blackbirds, as with all members of the Icteridae, are a New World species. As the most
northern member of the group, they breed across the entire North American boreal forest from
the west coast of Alaska to the east coast of Canada and Newfoundland. They breed as far north
as the tree line and south through central British Columbia, Alberta, Saskatchewan and Manitoba,
to southern Ontario and the northern Great Lakes, southern Quebec and northern New York and
New England (Avery, 1995). Historically, they were most abundant in the eastern boreal forest
(Greenberg and Droege, 1999). Their primary wintering range is the southeastern United States,
from eastern Texas, Oklahoma, Kansas and Nebraska, east to the Atlantic and Gulf coasts, south
to central Florida and north to southern Massachusetts. Their peak abundance stretches in a belt
from central Oklahoma to central North Carolina. (Avery, 1995, Hannah, 2005).
Migration
Annual northern migrations take place from March to May and southern migrations from
September to
November. They migrate diurnally and most often in flocks. These can be mixed species flocks
with other blackbirds, but often they are single-species (Avery, 1995). Flocks containing
thousands of individuals were often recorded in the early 20th century (Greenberg and Droege,
1999).
Habitat
The Rusty Blackbird’s dependence on forested wetlands makes them one of the most specialized
of the North American blackbirds (Avery, 1995, Greenberg and Droege, 1999). In the breeding
season, they are found in wet coniferous and mixed forests, frequently in fens, bogs, alder-willow
thickets, beaver ponds, muskeg and the edges of lakes and streams. During migration they are
common in open woodland, pasture, cultivated fields and wetland edges (Avery, 1995, Hannah,
2005). In the winter, they are dependent on wet woodlands, swamps and pond edges and usually
are not associated in large numbers with the enormous, mixed species roosts of other blackbirds
wintering in the southeast U.S. (Avery, 1995, Dolbeer, Woronecki, Stickley, White, 1978).
Breeding
Rusty Blackbirds are loosely colonial, often migrating in large flocks, but nesting in isolated,
monogamous pairs (Avery, 1995). Breeding densities are low throughout their range (Hannah,
2004) and nests have never been recorded closer than 0.4 miles (Avery, 1995). In Vermont, nestbuilding is known to begin in late April, with clutches starting in the first or second week of May
(Ellison, 1990). Usually 4-6 eggs are laid (Hannah, 2004) and are incubated solely by the
female. Incubation lasts for about 14 days and chick development is rapid (Avery, 1995), with
records of flight 13 days post-hatch. Fledglings have been recorded as early as the 12th of June in
Vermont (Ellison, 1990). One brood is raised per breeding season; however they will attempt
nests and clutches several times if initial attempts are unsuccessful (Avery, 1995).
The large, bulky nests are constructed solely by the female (Avery, 1995). The outer frame is
made of twigs, dried grasses and Usnea lichen (Avery, 1995, Nichols, 1985, Peterson, 1988) and
lined inside with 5-10 cm thick walls of wet, rotting vegetation. This is then lined with plant
fibers and dried grasses with the innermost layer made of fine green grasses. Completed nests
are typically 14-20 cm across and 8-9 cm deep. Nests are almost always located near water and
are .5-6m above the ground. Surrounding vegetation is dense and nests are often located against
tree trunks or among thick layers of small branches. The nests are most often placed in a spruce,
fir, tamarack, willow or alder (Avery, 1995). In Vermont, spruce and balsam fir are most
common, but Speckled Alder (Alnus rugosa), Willow (Salix spp.) and Sweet Gale (Myrica gale)
are also used (Nichols, 1985). Although nesting sites are returned to, nests are not reused in
subsequent years, but may be used by other species like the Solitary Sandpiper (Tringa solitaria)
(Avery, 1995, Granlund, 1991).
Diet
Rusty Blackbirds are opportunistic feeders throughout the year; however, during the breeding
season they are much more dependent on aquatic invertebrates and other high-nutrient animal
foods (Avery, 1995, Hannah, 2004). Their most common foods include insects and larvae, grain
crops, seeds, snails and crustaceans as well as fruits, fish and salamanders. They have also been
known to prey on other bird species during times of harsh weather and food shortage (Avery,
1995, Hannah, 2004). They are most commonly seen foraging on the ground, especially near
wetland edges, and in agricultural fields during migration (Avery, 1995). Their long-narrow bill
is well-adapted for an insectivorous diet, allowing them to loosen soil, dig through debris and
wade and plunge their heads into water after aquatic invertebrates (Avery, 1995, Orians, 1985).
Vocalization
Both male and female Rusty Blackbirds sing while on their breeding grounds (Avery, 1995). The
male has two songs that are often described as resembling a rusty hinge; paraphrased as “kush-alee” and “ksh-lay”, and also produce a loud “chack” note (Peterson, 2002). Females sing while
on the nest in response to the males, but their calls have not been described (Avery, 1995).
Current Status
Often described as abundant in the past, Rusty Blackbird populations appear to be in a major
decline that has been occurring for at least the past century. While no monitoring programs exist
for Rusty Blackbirds specifically, surveys like the Quebec Checklist Program, the Christmas Bird
Count and the Breeding Bird Survey, as well as various sources of ornithological literature
indicate an approximate decline of 90% in the past three decades and steady declines over the
past century (Droege and Greenberg, 1999). The most significant declines have occurred in the
eastern boreal forest and the Maritime Provinces of Canada (Hannah, 2004).
While many blackbird species have benefited from the expansion of agricultural and urban areas,
Rusty Blackbird populations have suffered due to their dependence on wooded wetlands and
aquatic invertebrates (Greenberg and Droege, 1999). It is estimated that 75% of the once nearly
contiguous bottomland forests of the lower Mississippi Valley have been converted to
agriculture, with the remaining patches of forests being highly fragmented (Loesch and Twedt,
1999). While this seems the most likely cause for declines, there is evidence suggesting that
changes in breeding habitat may also be contributing. Species such as the Horned Grebe
(Podiceps auritus) and Lesser Yellowlegs (Tringa flavipes), who also breed in boreal-type
wetlands, are showing similar declines (Hannah, 2004). Also, the rate of habitat loss has not kept
up with the rate of declines and population densities are falling in protected habitats as well
(Droege and Greenberg, 1999).
There are other hypotheses for factors that may at least have contributed to Rusty Blackbird
declines. Acidification of wetlands due to acid rain has been shown to affect calcium bearing
mollusk and insect species (Schindler, 1988). Calcium is essential for bone and eggshell
formation and a decrease in these important food sources may affect populations. Blackbird
control programs in agricultural areas of the southeastern United States, involving chemical
spraying of the immense, multi-species roosts wintering there, is a source of Rusty Blackbird
mortality (Greenberg and Droege, 1999). However, in a study done in the 1970’s documenting
species mortality in these roosts, Rusty Blackbirds represented less than one percent of the total
number of birds killed (Dolbeer, Stickley, White and Woronecki, 1978). The other roosting
species have shown much less, if any, decline (Greenberg and Droege, 1999). Competition from
other bird species on breeding grounds, primarily the Red-Winged Blackbird and the Common
Grackle, may also be contributing to reduced Rusty Blackbird numbers (Erskine, 1992, Avery,
1995). These birds are more aggressive and competitive and have shown dominant behavior over
Rusty Blackbirds (Ellison, 1990, Hannah, 2004). Due to the opening of forests, Grackles and
Red-Wings have gained access to wetland habitat that they historically would not have inhabited
(Wilcove and Whitcomb, 1983, Erskine, 1992, Avery 1995). Parasitism by the Brown-Headed
Cowbird is typically not a concern because Rusty Blackbirds tend to breed north of their range
and in different habitat types (Avery, 1995).
What is known about Rusty Blackbirds is they are in a decline that, according to surveys and
literature, is among the most significant of any North American species. Unfortunately, without
any monitoring programs it is difficult to notice long-term population changes and understand the
true reasons for their occurrence. Rusty Blackbird populations are listed as “demonstratably
secure” in the United States
National Heritage Status Rank, Canada National Heritage Status Rank and Global Heritage
Status Rank, they are not included on the National Audubon Society’s Blue List and are listed on
the American Bird Conservancy’s Green List as “moderately abundant, declining and with a high
degree of threat” (Hannah, 2004). There is no management of the species anywhere within its
range (Avery, 1995, Greenberg and Droege, 1997, Hannah, 2004). Their remote breeding
habitats, low population densities, broad distribution and relatively discreet habits do not bring
them into the forefront of most research and conservation efforts. However, with Audubon’s
Christmas Bird Count and the USGS Breeding Bird Survey both showing yearly declines
between 5 and 10 percent and similar population trend lines showing a drastic population crash
over the past forty years (Niven and Sauer, 2004), it is evident that Rusty Blackbirds need more
attention than they are currently receiving. Substantial research is needed on their life history,
breeding biology and population status (Greenberg and Droege, 1999). Without sufficient data
that is current, concrete and accurate, the Rusty Blackbird is not likely to receive the conservation
measures it may deserve.
Rusty Blackbird Research Proposal
Question
Through the collection of information on Rusty Blackbird breeding biology and distribution in
northeastern Vermont, what can be inferred about the causes of the current decline of this species
and how can these results contribute to future conservation efforts?
Objective
This project aims to assess the distribution and abundance of Rusty Blackbirds in northeastern
Vermont and add to the limited records of breeding biology information for this species. The
following questions will be addressed to establish this data:

Where and how are populations of Rusty Blackbirds distributed in northeastern
Vermont?

What is the breeding status of these populations?

How successful are breeding attempts in northeastern Vermont?

What types of wetlands are preferred by breeding Rusty Blackbirds in northeastern
Vermont?

What does the collection of vegetation and water quality data around nest locations

tell about breeding habitat preference?
What can be inferred about the Rusty Blackbird’s food preferences, home range,
behavior and interaction with other species through observation in the field?
Vermont Summary
Very little is known about Rusty Blackbird breeding biology. Until 2006 there had only been
two studies done on the species in their breeding grounds. The first of these studies occurred in
1920 and measured re-nesting attempts after nest destruction. The only other study, done by
Walter Ellison, occurred in Vermont in 1990. This study surveyed Rusty Blackbird locations
found during the Vermont Breeding Bird Atlas and has contributed the majority of breeding
observations of the species.
Last year marked the beginning of a concerted effort to gather field information on Rusty
Blackbirds. This year, 2007, will host the most extensive studies to date and build a framework
of information for future study. Breeding ground research in 2007 will occur in the northeastern
United States, Alaska and Alberta, Canada.
The Vermont Breeding Bird Atlases provide an overall sense of the distribution of Rusty
Blackbirds in Vermont. The first atlas, conducted from 1979 to 1983, found Rusty Blackbirds at
46 locations with 14 cases of confirmed breeding. The second atlas project began in 2003 and
will be completed this year. So far, there have been 26 sightings with 13 cases of confirmed
breeding.
The atlases indicate two centers of Rusty Blackbird population in the state; in the southern Green
Mountains and in the highlands of the Northeast Kingdom. Only 8 sites, 4 with confirmed
breeding, have recorded Rusty Blackbirds in both atlases. While their disappearance is occurring
in both regions, the south appears more severe as most new occurrences are in the northeast
portion of the state.
Conducting Surveys
This project is focused on Orleans, Caledonia and Essex counties located in northeastern
Vermont. Data from the Vermont Breeding Bird Atlas is indicating this to be the primary
breeding range of Rusty Blackbirds in Vermont. In 2007, field surveys in the northeastern U.S.
will be taking place in Maine, New Hampshire, Vermont and New York. There is effort to
standardize the research methods being used for all northeastern surveys. This project will
follow protocols created by the Maine Department of Inland Fisheries and Wildlife (see Appendix
A). All surveys will take place between May 10th and June 18th, 2007.
A typical survey will involve accessing a point that provides an unobstructed view of as much of
the wetland as possible. A five minute period of passive observation will be conducted from this
point, followed by a recording of all available information for the data sheet. A broadcast of
Rusty Blackbird calls and a three minute observation period will follow. A large wetland may
require two surveys. One datasheet will still be used for these wetlands and the coordinates of
both broadcast sites will be recorded. If there is no response then the survey is over upon
completion of the data sheet. Rusty Blackbird response to the callback necessitates as much
observation of the individual as possible, with the recording of all notable behaviors and
determination of breeding status.
Site Selection
Survey sites need to be selected randomly so as to gain a better sense of Rusty Blackbird
distribution and preference of wetland type. The project area will be divided using 7.5 minute
USGS topographic maps. Two wetlands will be randomly selected for every map that is more
than 50% within the project area. One site will be selected for maps less than 50% in the project
area.
Nest Success
The purpose of nest success surveys is to gain a better understanding of breeding biology and,
ultimately, to see if nest attempts are successful. Surveys involve locating a Rusty Blackbird nest
and periodically checking on it (at least three times) during the breeding season. The surveys
should record the development of chicks while in the nest and the number of chicks that fledged.
These surveys will be conducted in known locations of Rusty Blackbird breeding in the
Nulhegan Basin, Victory Basin and/or Ferdinand Bog.
Nest Vegetation and Water Quality Surveys
Vegetation and water quality surveys will be done at the same nests being used for nest success
surveys. This research will be conducted within a given area around nest sites and will consist of
identification of surrounding vegetation, assessment of foliage height diversity and canopy cover.
Water samples will be taken from the closest surface water to the nest. Tests will be done for pH,
temperature and macro-invertebrate populations. Surveys will follow a protocol developed by
the Maine Department of Inland Fisheries and Wildlife.
Non-Random and Road Surveys
Since it is also valuable to know the location of as many breeding Rusty Blackbirds as possible,
additional surveys may take place in areas of suitable habitat. Selection of these sites will be
through personal discretion. Roadside surveys will comprise many of these sites since wetlands
near roads provide easy access and can allow for many additional surveys. Results from these
surveys will not be included in the results from randomly selected sites.
Materials and Budget
Permission for use by Sterling College - Broadcaster, GPS unit, meter tape, and pH meter.
Personally owned items - field guides, binoculars, car, field notebook, and camera.
Items needed to purchase- Gas (40 gallons at $2.50/gallon)……………………$100.00
Food……………………….………………………..$200.00
Slide Film and Development…………….…………$100.00
Total…. $400.00
Dissemination
The results of this project will be submitted to Laura Deming of the New Hampshire Audubon
Society. Other groups working within Vermont and the northeast, or working specifically with
Rusty Blackbirds, will also be given access to this data. The report will focus on the results of
wetland surveys and nest success. Analysis will be done on all recorded breeding biology
observations, including vegetation and water quality surveys, preferred wetland types, forage
preferences, species interactions and all recorded protocol data.
Survey Timeline
May 10th-11th
-Craftsbury, Lowell, Irasburg
May 14th-20th
-North Troy, Newport, Caspian Lake, Crystal Lake, Stannard, Sutton, Joe’s Pond, Lyndonville
-One trip to either Ferdinand Bog or Victory Basin to locate nests for nest success surveys
May 21st-27th
-Marshfield, Peacham, Barnet, Orleans, West Charleston, Westmore, Miles Pond, Gilman,
Concord
May 28th- June 3rd
-Morgan Center, Averill, Norton Pond, Monadnock Mountain
-Nest success surveys in Ferdinand Bog, Victory Basin and/or Nulhegan Basin
June 4th-10th
-Island Pond, Spectacle Pond, Bloomfield, Seneca Mountain
-Nest success surveys in Ferdinand Bog, Victory Basin and/or Nulhegan Basin
June 11th-17th
-Maidstone Lake, Stratford, Gallup Mills, Stone Mountain
-Nest success surveys in Ferdinand Bog, Victory Basin and/or Nulhegan Basin
*This timeline is subject to change due to weather, time constraints and progression of the
nesting period.
**If habitat and nest surveys are not providing enough data for this project to be worthwhile,
there is the option of doing a radio-telemetry study. A telemetry study involves capturing birds,
attaching a radio transceiver to them and following them in the field for three days. This study
would focus on 1-3 breeding pairs. A two-day training session in Maine would be required prior
to conducting a telemetry study. At the end of May an update of the project’s progression will be
provided to the committee to determine if the surveys are providing sufficient data.
Literature Cited
Adamus, P.R. 1987. Atlas of Breeding Birds of Maine. Maine Department of Inland Fisheries
and Wildlife, Augusta, Maine.
Avery, Michael. 1995. Rusty Blackbird. The Birds of North America. The Academy of Natural
Sciences, Philadelphia.
Bogo, Jennifer, Niven Dan, Sauer, John. 2004. Trendsetting: Rusty Blackbird. Audubon. 106:5
Dolbeer, Richard, Stickley, Allen, White Stephen and Woronecki, Paul. 1978. Agricultural
Impact of a Winter Population of Blackbirds and Starlings. The Wilson Bulletin. 90:1
Droege, Sam and Greenberg, Russell. 1999. On the Decline of the Rusty Blackbird and the Use
of Ornithological Literature to Document Long-Term Population Trends. Conservation Biology.
13:5
Erskine, A.J. 1992. Atlas of Breeding Birds of the Maritime Provinces. Nimbus Publications
and the Nova Scotia Museum, Halifax.
Granlund, James. 1991. Rusty Blackbird. The Atlas of Breeding Birds of Michigan. Michigan
State University Press, MI.
Hannah, Kevin. 2004. Status Review and Conservation Plan for the Rusty Blackbird. Alaska
Bird Observatory. Fairbanks, Alaska.
Herman, Heather and Hodgman, Thomas. 2002. Maine Rusty Blackbird Report. Maine
Department of Inland Fisheries and Wildlife, Bangor, Maine.
Loesch, Charles and Twedt, Daniel. 1999. Forest Area and Distribution in the Mississippi
Alluvial Valley: Implications for Breeding Bird Conservation. Journal of Biogeography, 26:6
Nichols, W.D. 1985. Rusty Blackbird. The Atlas of Breeding Birds of Vermont. University Press
of New England, Hanover, NH.
Peterson, John. 1988. Rusty Blackbird. The Atlas of Breeding Birds of New York State. Cornell
University Press, Ithaca.