J Ornithol
DOI 10.1007/s10336-016-1330-x
ORIGINAL ARTICLE
Patterns of nest attendance by female Greater Prairie-Chickens
(Tympanuchus cupido) in northcentral Kansas
Virginia L. Winder1 • Mark R. Herse2 • Lyla M. Hunt2 • Andrew J. Gregory3
Lance B. McNew4 • Brett K. Sandercock2
•
Received: 3 June 2015 / Revised: 21 January 2016 / Accepted: 2 February 2016
Ó Dt. Ornithologen-Gesellschaft e.V. 2016
Abstract Nest attendance behavior is a critical component of avian ecology that influences nest survival and
population productivity. Birds that provide uniparental care
during incubation and brood-rearing must balance the
benefit of reproductive success with the costs of physiological needs and predation risk. We used miniature nest
cameras to record 5904 h of video footage at 33 nests of
Greater Prairie-Chickens (Tympanuchus cupido) during
2010 and 2011 in northcentral Kansas. We quantified the
timing and duration of incubation bouts to address alternative hypotheses about physiological requirements and
predation risk as drivers of incubation behavior. We also
identified nest predators and determined timing of predation events, and tested for effects of nest attendance and
monitoring technique on nest survival (video vs. telemetry). Female prairie chickens exhibited high incubation
constancy per day (*95 %) and typically took two *40min recesses per day: one after sunrise and one before
sunset. Mesocarnivores were responsible for 75 % (18 of
24) of nest losses, and most nest predation events occurred
during crepuscular or overnight hours. Controlled
Communicated by C. G. Guglielmo.
& Virginia L. Winder
vwinder@benedictine.edu
1
Department of Biology, Benedictine College, Atchison,
KS 66002, USA
2
Division of Biology, Kansas State University, Manhattan,
KS 66506, USA
3
School of Environment and Society, Bowling Green State
University, Bowling Green, OH 43403, USA
4
Department of Animal and Range Sciences, Montana State
University, Bozeman, MT 59717, USA
comparisons provided no evidence that video surveillance
attracted predators to nests. Variation in nest attendance
had a minimal effect on nest survival compared to height of
vegetative cover at the nest site. Timing of recesses did not
indicate avoidance of predator activity in our study system.
The bimodal pattern of incubation breaks observed in most
grouse species is likely driven by physiological requirements of the female rather than predation pressure. Female
Greater Prairie-Chickens appear to prioritize their metabolic needs and future reproductive potential over current
nest survival.
Keywords Grouse Incubation behavior Nest survival Physiology Predation
Zusammenfassung
Muster der Nestbewachung bei Präriehuhn-Weibchen
Tympanuchus cupido in Nordzentral-Kansas
Nestbewachungsverhalten ist ein entscheidender Bestandteil der Ökologie von Vögeln, welcher Einfluss auf Nesterfolg und die Produktivität einer Population hat.
Vogelarten, bei denen sich nur ein Elternteil um Bebrütung
und Jungenaufzucht kümmert, müssen den Gewinn durch
reproduktiven Erfolg gegen die Kosten physiologischer
Ansprüche und des Prädationsrisikos abwägen. Mithilfe
von Miniatur-Nestkameras filmten wir in den Jahren 2010
und 2011 5.904 Stunden Videomaterial an 33 Nestern von
Präriehühnern (Tympanuchus cupido) in NordzentralKansas. Wir bestimmten Zeitpunkt und Dauer der
Bebrütungsphasen, um alternative Hypothesen zu physiologischen Bedürfnissen und Prädationsrisiko als den treibenden Faktoren für das Brutverhalten anzusprechen.
Außerdem ermittelten wir die Nesträuber sowie den
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Zeitpunkt der Prädationsereignisse und überprüften den
Einfluss von Nestbewachung und Überwachungstechnik
(Video beziehungsweise Telemetrie) auf die Erfolgsraten
der Nester. Präriehuhn-Weibchen wiesen eine hohe Brutkonstanz am Tag auf (etwa 95 %), und machten typischerweise zwei etwa 40-minütige Brutpausen: eine nach
Sonnenaufgang und eine vor Sonnenuntergang. Mesocarnivoren waren für 75 % (18 von 24) der Nestverluste
verantwortlich, und die meisten Prädationsereignisse fanden zur Dämmerung oder während der Nachstunden statt.
Kontrollvergleiche ergaben keine Hinweise darauf, dass
durch die Videoüberwachung Prädatoren zu den Nestern
gelockt wurden. Die Variation bei der Nestbewachung
hatte, verglichen mit der Vegetationshöhe am Neststandort,
nur einen minimalen Effekt auf den Nesterfolg. Der Zeitpunkt der Brutpausen deutete in unserem Untersuchungssystem nicht auf Vermeidung von Prädatorenaktivität. Das
bimodale Muster der Brutpausen, wie man es bei den
meisten Raufußhühnern beobachten kann, wird vermutlich
eher von physiologischen Bedürfnissen des Weibchens
bestimmt als durch den Prädationsdruck. PräriehuhnWeibchen scheinen somit ihrem Stoffwechselbedarf und
zukünftigem Fortpflanzungspotenzial mehr Bedeutung
einzuräumen als dem gegenwärtigen Nesterfolg.
Introduction
Evolutionary pressures of minimizing predation risk while
meeting physiological needs of parents and offspring have
shaped reproductive decisions for many animal species
(Wiebe and Martin 2000; Gowaty and Hubbell 2009). Nest
attendance behavior determines individual reproductive
success and population productivity, but is a difficult
component of avian reproduction to study (Conway and
Martin 2000; Deeming 2002; Benson et al. 2010; EllisFelege and Carroll 2012; Thompson and Ribic 2012).
Incubating parents typically take at least one foraging
recess each day, but recess timing and duration are flexible
behaviors that can be adjusted based on the physiological
requirements of the incubating parent, eggs, or young
(Cartar and Montgomerie 1985, 1987; Erikstad 1986;
Wiebe and Martin 1997; Caudill et al. 2014; Hovick et al.
2014), as well as predation risk to parents or their offspring
(Ghalambor and Martin 2002; Tulp and Schekkerman
2006; Coates and Delehanty 2008). Moreover, priorities of
incubating parents can be shaped by interactions among
weather, energetics, and predation risk (Cartar and Montgomerie 1987; Wiebe and Martin 1997; Tulp and
Schekkerman 2006; Smith et al. 2012a, b; Caudill et al.
2014). Benefits of current reproductive output must be
balanced against risks to parental survival and potential
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loss of future reproductive success. It can be difficult to
disentangle the intrinsic and extrinsic factors that influence
nest attendance behavior, but in some long-lived bird
species, adult survival and residual reproductive value are
prioritized over current reproductive success (Tulp and
Schekkerman 2006).
Nest attendance is often the most energetically expensive phase of the breeding season for species with uniparental incubation (Walsburg 1983). Females of largebodied species of grouse make a sizeable parental investment in a large clutch of energy-rich eggs and provide sole
parental care during incubation and rearing of precocial
young. Thus, females must balance physiological requirements and predation risk when making decisions about
incubation behavior (Coates and Delehanty 2008; EllisFelege and Carroll 2012). For many species of grouse, nest
survival is a key component of population viability, and the
greatest impacts to population growth come from loss of
eggs to predators during incubation (Wiebe and Martin
1997; Wisdom and Mills 1997; Sandercock et al. 2005;
Coates and Delehanty 2008; McNew et al. 2011a, 2012).
High nest predation rates can be a strong selective pressure
shaping incubation behavior, and many species of birds
have evolved flexible strategies for predator avoidance
(Conway and Martin 2000; Ghalambor and Martin 2000;
Martin 2002).
The Greater Prairie-Chicken (Tympanuchus cupido,
hereafter ‘prairie chicken’) is an indicator species for
tallgrass prairie ecosystems in North America and is listed
as Vulnerable by the International Union for Conservation
of Nature and is state-listed in parts of its extant range
(Poiani et al. 2001; Johnson et al. 2011; BirdLife International 2014). Female prairie chickens mate with males at
leks, and then select nest sites with favorable microclimates and intermediate vegetative cover (Nooker and
Sandercock 2008; Matthews et al. 2013; Hovick et al.
2014; McNew et al. 2014, 2015). Prairie chickens are a
ground-nesting species, and habitats selected by females
reflect a balance between concealment of the nest, maintaining lines of sight to detect predators, and shelter with a
favorable microclimate. Females lay 10–15 eggs at a rate
of 1 egg per day before incubating the clutch for *25 days
(Hamerstrom and Hamerstrom 1973; Johnson et al. 2011;
McNew et al. 2011b). Thus, prairie chickens have high
reproductive potential but remain vulnerable to predators
during the *38-day nesting cycle.
Past studies of nest attendance in grouse have relied on
direct observations or data loggers, and our study is the first
to use video camera technology to investigate nest attendance behaviors of prairie chickens. Our study addressed
four objectives. First, we quantified the timing and duration
of incubation bouts and recesses away from the nest. If
incubation patterns were related to predation risk, we
J Ornithol
predicted females would leave nests once per day to forage
around midday and avoid crepuscular periods with the
highest activity of diurnal nest predators (Cartar and
Montgomerie 1987; Coates and Delehanty 2008; Burnam
et al. 2012). Nest attendance behavior could also be related
to the physiological needs of either the incubating parent or
offspring. If nest attendance behaviors were driven by the
digestive physiology and metabolic requirements of the
incubating parent, we predicted females would take
recesses at dawn and dusk to feed and eliminate fecal waste
(Keppie and Herzog 1978; Wiebe and Martin 1997).
Alternatively, if nest attendance behaviors were driven by
the thermoregulatory needs of developing offspring, we
predicted females would take recesses at midday to minimize egg cooling and avoid the potential costs of reheating
eggs (Cartar and Montgomerie 1985, 1987; Reed et al.
1995; MacCluskie and Sedinger 1999; Schmidt et al. 2005;
Tulp and Schekkerman 2006). In hot environments,
females might take recesses around dawn during the
coolest period of the day to minimize egg exposure to high
temperatures (Wiebe and Martin 1997; Hovick et al. 2014).
Second, we identified nest predators and monitored timing
of predation events. Based on egg remains and signs of
predator activity at nest sites, we predicted that nest
predators would be mesocarnivores with greater activity
during crepuscular periods (Ashby 1972; Wiebe and Martin
1997; Pietz et al. 2012). Third, we tested whether nest
survival was influenced by nest attendance behaviors of
incubating females (Wiebe and Martin 1997; Smith et al.
2012a). We hypothesized that nests by females that took
fewer recesses and maintained higher incubation constancy
would have higher daily survival rates (Ghalambor and
Martin 2002; Smith et al. 2012a). Last, deploying nest
cameras raises potential concerns about negative effects of
video-monitoring equipment on nest survival (Richardson
et al. 2009; Pietz et al. 2012; Powell et al. 2012). We
compared survival rates of nests monitored with video
equipment versus nests monitored remotely by telemetry. If
the presence of video equipment attracted predators or
increased the rate of nest abandonment, we predicted
video-monitored nests would experience lower nest survival rates than unmanipulated nests.
Methods
Study area
During the breeding seasons of 2010 and 2011, we monitored the incubation behavior of female Greater PrairieChickens at a *1300 km2 field site south of Concordia in
the Smoky Hills region of northcentral Kansas (Fig. 1).
The landscape in our study area was dominated by native
grasses managed for cattle production (58 %) and row crop
agriculture (35 %). Road density was relatively high
throughout the study area at 1.4 km of road per km2.
Weather conditions during our 2-year study were similar
between years (Winder et al. 2014).
Field methods
We captured prairie chickens at leks using drop-nets and
walk-in traps during a 3-month period from March to May
of 2010 and 2011. We identified second-year (SY) birds by
pointed tips and spotting on the outer two primaries vs.
after-second-year (ASY) birds with rounded tips and less
spotting on the outer two primaries (Henderson et al.
1967). Females were equipped with a necklace-style VHF
radio-transmitter (10–11 g; Model A3950, ATS, Islanti,
MN), a uniquely numbered metal leg band, and three colored leg bands. Radio-marked females were located 4–7
times a week by triangulation with VHF receivers (Model
R2000, ATS, Islanti, MN) and handheld yagi antennas.
When females were triangulated in the same location
for [2 consecutive days, we used portable receivers to
approach on foot and locate nests. We recorded UTM
coordinates at the nest using a handheld GPS unit (±5 m).
If nests were discovered during egg laying, we assumed an
egg-laying rate of one egg per day and recorded the exact
date for initiation of incubation. For nests that were located
after incubation had been initiated, we estimated nest initiation dates by floating eggs in lukewarm water and by
comparing egg buoyancy to a standardized flotation curve
(±1 to 2 days; McNew et al. 2009).
We monitored a subset of nests with color, low-resolution security cameras with infrared capabilities (950 nm,
Model ENC-100, EZ Spy Cam, Los Angeles, CA), powered by two 12 V 26AH car batteries. We mounted a
camera at the edge of the nest bowl using a camouflaged
metal stake. We housed all recording equipment inside a
camouflaged plastic container *25–30 m away from the
nest, and buried the power cord in a shallow trench covered
with vegetation. The camera installation process usually
took less than 1 h (‘‘Appendix 1’’). We visited videomonitored nests (hereafter, ‘video nests’) every 3 days to
replace batteries and memory cards. Females were not
flushed during visits to check recording equipment, but
were observed via a live portable viewfinder. If a female
was absent and the nest status was uncertain, we watched
recent footage on the viewfinder to check for signs of
predation, nesting activity, or hatching. If nest fate was not
captured on camera, we used eggshell fragments, predator
sign, and other evidence at the nest bowl to assign nest fate.
We considered nests to be successful if C1 chick hatched
and left the nest, or failed if none of the eggs produced
young. Once the nest attempt was complete, we recorded
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Fig. 1 Map of the study area
for monitoring patterns of nest
attendance of female Greater
Prairie-Chickens in northcentral
Kansas, 2010 and 2011.
Females were trapped at leks
(black triangles) and marked
with VHF radios. We analyzed
nest survival for nests
monitored with video cameras
(white circles) compared to a
subset of nearby nests
monitored via radio telemetry
(gray squares). Light gray
shading is native grasslands
managed as rangelands for
cattle grazing; dark gray
shading is row crop agriculture,
and each square is a section of
land (1 mi2)
visual obstruction readings (VOR) at the nest site as an
index of vegetative biomass and nest concealment (Robel
et al. 1970).
Video annotation
We reviewed nest footage with a VLC media player (ver.
2.0.0, VideoLan, Paris, France). For all nest events, we
determined the nest age as days since incubation was initiated, ordinal date, and time of day in relation to sunrise
and sunset (US Naval Observatory 2016; data for Concordia, Kansas). Our 24-h periods began at midnight and
ended at 23:59 on the same calendar day, and we considered the periods ±90 min of sunrise or sunset as crepuscular. We calculated incubation constancy as the
percentage of a 24-h period a female spent incubating eggs
per day, and total recess duration as the total time away
from a nest in a 24-h period. We defined incubation as a
female present at an active nest for C1 min, and a recess as
a female being absent from an active nest for C1 min. We
identified nest predators to species from video footage, and
defined total loss as a predator consuming an entire clutch
or killing the incubating female. We defined partial loss as
a predator consuming a subset of eggs from a nest that
remained active following the predation event. We defined
unsuccessful predation as a snake or other predator
unsuccessfully attempting to consume eggs. One observer
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(LMH) annotated video footage for ten nests, and a second
observer (MRH) annotated footage for the remaining 23
nests. Both observers independently annotated video footage for eight nests (24 %). We used the overlapping subset
to check for consistency between observers and found
complete agreement in video annotation between
observers.
Data analysis
Nest attendance
We limited our analyses of nest attendance behavior (incubation constancy, total daily recess duration, and number
of recesses per day) to nests that had C1 day of continuous
video footage that was uninterrupted by camera malfunction, loss of power, or disturbance from changing batteries
and memory cards. Most nests were monitored for [1 day,
and we further limited our analyses to days with continuous, uninterrupted footage. We monitored two nests within
the same year for one female and two nests in separate
years for a different female but accepted limited pseudoreplication to use our complete dataset. As a first step,
we compared age-class specific generalized additive models (GAMs) in the package mgcv of Program R to compare
incubation behavior between two female age-classes (results not shown). We found no evidence for differences
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between SY and ASY females and pooled age-classes for
subsequent analyses. We used GAMs to test for effects of
timing of recess initiation on recess duration (ver. 2.15.1, R
Foundation for Statistical Computing, Vienna, Austria;
Wood 2011). We also used GAMs to test for effects of
ordinal date, nest age, and VOR on incubation constancy.
We explored models of nest attendance with fixed effects
and with an individual nest as a random effect, and found
no difference in the significance outcome when random
effects were added. Our main interest was in understanding
the overall patterns in prairie chicken behavior. Therefore,
we present results from fixed effects models, which
allowed us to generate the predictive relationship for nest
attendance behavior.
Nest survival
Nest monitoring in our 2-year study spanned a 78-day
nesting period from 18 April to 4 July. We used the
package RMark in Program R as an interface to the nest
survival procedure of Program MARK to model effects of
female nest attendance and monitoring method on daily
nest survival (White and Burnham 1999; Dinsmore et al.
2002; Laake and Rexstad 2008). All models were constructed using the logit-link function, and model selection
was based on differences in AICc (DAICc) and evidence
ratios from Akaike weights (wi; Burnham and Anderson
2002). We discarded models with DAICc B2 that differed
from the top model by a single parameter if predictors were
uninformative parameters with confidence intervals for
slope coefficients (b) that included zero (Burnham and
Anderson 2002; Arnold 2010).
We used two separate model sets to explore daily survival rates of prairie chicken nests. The goal of our first set
of nest survival models was to assess the potential effect of
nest attendance behavior on nest survival. We limited our
analysis to nests for which we had continuous, uninterrupted video footage for C1 day (25 nests of 23 females).
We included VOR as a factor because vegetative cover at
the nest has been found to explain variation in nest survival
(McNew et al. 2014, 2015). Rainfall and storm events can
result in direct loss of nests due to flooding or hail, or
indirect losses of nests if scent-based predators detect
females with damp plumage (Flanders-Wanner et al. 2004;
Fields et al. 2006; Webb et al. 2012; McNew et al. 2014).
We modeled the effect of precipitation on nest survival using data from a nearby (*35 km) NOAA weather
station at the Concordia Blosser Municipal Airport
(USW00013984, http://www.ncdc.noaa.gov). During our
2-year study, many nest losses occurred between midnight
and sunrise. For overnight predation events, precipitation
during the previous calendar day could play a role in the
probability of a predator detecting a nest. Thus, we combined daily precipitation from the current and previous day
to create a time-varying covariate for each day of our nest
monitoring period. We modeled main effects and interactions of mean incubation constancy, mean number of
recesses per day, VOR, and precipitation on daily survival
rates of prairie chicken nests.
In a second set of models, we compared video vs.
unmanipulated nests to test for potential negative effects
of video-monitoring on nest survival. Video nests had a
disturbance from camera installation plus visits
every *3 days when females occasionally flushed. For
unmanipulated nests, we flushed the female from the nest
once in early incubation and subsequently monitored nests
via telemetry at distances of C100 m. We used Hawth’s
Tools for ArcMap (ver. 9.3) to match each video nest with
the nearest unmanipulated nest as a control (Fig. 1; spatialecology.com/htools; ESRI, Redlands, California; Beyer
2004). Renesting females remained close to their previous
nest attempt, and we excluded replacement clutches by the
same individual in our matched pairs design. Our matched
set of unmanipulated nests included nest attempts by 33
unique females, and none of these females were included in
our dataset of video nests. We modeled the main effects of
the nest monitoring method (video vs. telemetry) and
interactions with VOR and precipitation on daily nest
survival of prairie chickens. We compared overall nest
survival between video vs. telemetry nests by extrapolating
the product of daily survival probabilities for each monitoring group to a 38-day exposure period, and by calculating variances of the extrapolated estimates with the delta
method (Powell 2007).
Results
Nest attendance
We included 5904 h of video footage (2010: n = 1848;
2011: n = 4056) in our analyses of nest attendance of
Greater Prairie-Chickens. Our sample included 464 incubation recesses (2010: n = 151; 2011 n = 313) during 246
complete monitoring days at 25 prairie chicken nests
(2010: n = 7; 2011: n = 18) attended by 23 females. Mean
incubation constancy per day was 94.9 % ± 0.3 SE (range
61.0–99.8 %), and typically exceeded 90 % regardless of
vegetative cover at the nest (F1,244 = 4.28, P \ 0.0001,
adjusted r2 = 0.11; Fig. 2a). Females took an average of
1.87 ± 0.04 recesses per day (range 1–4), and each recess
duration averaged 39 ± 2 SE min (range 1–479 min).
Female prairie chickens exhibited a bimodal distribution of
recess timing with most recesses taking place within the
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Fig. 2 Generalized additive models for the effects of visual obstruction reading (VOR, a), ordinal date (b), and nest age (c) on incubation
constancy (percent of 24-h period spent incubating eggs) of female
Greater Prairie-Chickens in northcentral Kansas, 2010 and 2011
(n = 25 nests attended by 23 individual females). Circles observed
incubation constancy; solid line predicted line of best fit from a
generalized additive main effects model for VOR, ordinal date, or
nest age; dotted lines upper and lower 95 % confidence intervals
Fig. 3 Timing (a) and duration (b) of incubation recesses for female
Greater Prairie-Chickens nesting in northcentral Kansas, 2010 and
2011 (n = 464 recesses from 25 nests attended by 23 individual
females). Light gray boxes indicate crepuscular periods within 90 min
of sunrise and sunset (vertical dashed lines), and dark gray box
indicates nighttime hours. Key for panel a: black star predation event
resulting in total clutch loss; white star predation event resulting in
partial clutch loss; open circle unsuccessful predation attempt.
Placement of symbols is approximate for nighttime events because
the duration of nighttime hours varied over the breeding season. Key
for panel b circles observed recess duration (gray recesses before
sunset, P = 0.003; white recesses near sunrise, P \ 0.0001); solid
lines predicted lines of best fit from generalized additive main effects
models for timing of recess initiation; dotted lines upper and lower
95 % confidence intervals. Two recesses with durations [300 min
were omitted from the figure for clarity. Data for timing of sunrise
and sunset at Concordia, Kansas were obtained from the US Naval
Observatory (2016; http://aa.usno.navy.mil/)
3-h period after sunrise and the 3-h period before sunset
(Fig. 3a). About one-third of all recesses (32 %, 147 of
464) occurred within the 90-min period after sunrise or
before sunset (Fig. 3a). Only three incubation recesses
occurred before sunrise, and no recesses occurred after
sunset (Fig. 3a).Total recess duration per day was unaffected by timing of recess initiation (GAMs: morning
recess duration *minutes after sunrise, F1,200 = 35.35,
P \ 0.0001, adjusted r2 = 0.45; evening recess
duration *minutes
before
sunset,
F1,262 = 3.67,
P = 0.003, adjusted r2 = 0.06; Fig. 3b).
Number of recesses per day was not related to nest age
(F1,244 = 2.59, P = 0.11, adjusted r2 = 0.006) or ordinal
date of the season (F1,244 = 0.14, P = 0.71, adjusted
r2 = 0.004). We observed slightly lower rates of incubation constancy at the start and end of the breeding season
(F1,244 = 28.3, P \ 0.0001, adjusted r2 = 0.72; Fig. 2b).
Similarly, we found lower rates of incubation constancy at
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Fig. 4 Still photographs captured from video footage at nests of
Greater Prairie-Chickens in northcentral Kansas, 2010 and 2011.
Female Greater Prairie-Chicken returning to nest after incubation
break (a), female leaving nest with chicks (b), coyote (Canis latrans;
c), bullsnake (Pituophis catenifer; d), American badger (Taxidea
taxus; e), striped skunk (Mephitis mephitis; f)
the start and end of the 38-day in the nesting cycle
(F1,244 = 2.10, P = 0.04, adjusted r2 = 0.05; Fig. 2c).
sunrise and sunset (9 of 24, 38 %; Fig. 3a). Four of six
predation events during daytime hours were by snakes
(Fig. 3a; ‘‘Appendix 2’’).
Predation resulted in total clutch loss in 20 of 24 events
(83 %). We observed two cases of partial predation, and
both occurred at night. One nest was partially consumed by
a Virginia opossum (Didelphis virginiana), and then
completely consumed 14 days later by a striped skunk
(Mephitis mephitis; Fig. 4f). A second nest was partially
consumed by a bullsnake and then completely consumed 1
day later by a striped skunk. We also observed two
unsuccessful predation events, during daytime hours. A
thirteen-lined ground squirrel (Ictidomys tridecemlineatus)
was unsuccessful at removing eggs during a female recess,
Predation events
We recorded 24 predation attempts at 33 nests of prairie
chickens (Fig. 4). Coyotes (Canis latrans; n = 9) and
bullsnakes (Pituophis catenifer, n = 5) were the most
common predators and accounted for 58 % of total losses
(Fig. 4c, d, ‘‘Appendix 2’’). All predation events occurred
while the female was present at the nest, and the incubating
female was killed in 2 of 9 attacks by coyotes. Threequarters (18 of 24) of all nest predations occurred at night
(9 of 24, 38 %) or during crepuscular periods around
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Table 1 Model selection to
evaluate the effects of mean
incubation constancy, mean
number of recesses per day,
visual obstruction reading
(VOR), and precipitation on
survival of Greater PrairieChicken nests in Kansas during
2010 and 2011 (n = 5904 h and
25 nests)
Model factors
ka
Deviance
DAICbc
wi
VOR
2
132.19
0.00
0.26
VOR ? incubation constancyc
3
131.55
1.38
0.13
VOR ? number of recesses per dayc
3
131.98
1.81
0.10
Constant
1
136.03
1.82
0.10
VOR ? precipitationc,d
3
132.17
2.00
0.10
VOR 9 incubation constancyc
4
130.18
2.04
0.09
VOR 9 number of recesses per dayc
4
130.99
2.86
0.06
Number of recesses per day
2
135.42
3.23
0.04
Incubation constancy
2
135.77
3.57
0.04
Precipitationd
2
136.02
3.82
0.04
Incubation constancy ? number of recesses per dayc
3
135.11
4.94
0.02
a
k = number of parameters, deviance = -2lnL
b
Minimum AICc = 136.22
c
Models with uninformative parameters that were not competitive with the top model (Arnold 2010)
d
Daily precipitation data were from a weather station at Concordia Blosser Municipal Airport
(USW00013984, http://www.ncdc.noaa.gov)
our candidate set included the effect of VOR on nest survival (wi = 0.26, b = 0.75, 95 % CL -0.05, 1.56;
Table 1). We found a weak negative relationship between
daily nest survival and mean number of recesses per day
(wi = 0.05; b = -0.30, 95 % CL -1.03, 0.43; Fig. 5), but
this feature of nest attendance behavior did not improve
model fit compared to a constant model (wi = 0.10; wi/
wj = 2.0; Table 1). Nest survival was not affected by
variation in incubation constancy (wi = 0.04; b = -0.003,
95 % CL -0.02, 0.01) or precipitation (wi = 0.04;
b = 0.01, 95 % CL -0.25, 0.28; Table 1).
Fig. 5 Relationship between daily nest survival and mean number of
incubation recesses per day. We modeled nest survival for 25 Greater
Prairie-Chicken nests monitored in northcentral Kansas during 2010
and 2011. Solid line daily nest survival from a main effects model
with mean number of recesses per day; dotted lines upper and lower
95 % confidence limits
and a massasauga rattlesnake (Sistrurus catenatus)
attempted but was unable to ingest eggs from a nest after
flushing the attending female.
Nest survival
Effects of nest attendance
We included 25 nests in our first nest survival analysis
(2010 = 7 and 2011 = 18). Nine of 25 (36 %) nests successfully produced C1 chick. The best supported model in
123
Effects of monitoring technique
We matched 33 video nests with 33 unmanipulated nests to
test for effects of monitoring technique on nest survival.
Median distance from a video nest to the nearest unmanipulated nest was 1.2 km (range 0.1–8.1 km). Nine of 33
(27 %) video nests successfully produced C1 chick vs. 8 of
33 (24 %) unmanipulated nests (Fisher’s exact test,
P = 1.0). Nest monitoring method did not improve model
fit, and 95 % confidence limits for our estimate of the
effect of monitoring method overlapped zero (wi = 0.05;
b = 0.22, 95 % CL -0.36, 0.79; Table 2). Contrary to our
predictions, video nests tended to have higher 38-day survival rates (0.17 ± 0.06) than unmanipulated nests
(0.11 ± 0.05). Vegetative cover (VOR) was the only predictor in the best supported model (wi = 0.28) and was the
best overall predictor of daily nest survival in our model set
J Ornithol
Table 2 Model selection to
evaluate the effects of nest
monitoring technique (videomonitored vs. unmanipulated),
visual obstruction reading
(VOR), and precipitation on
daily survival of Greater PrairieChicken nests in Kansas during
2010 and 2011 (n = 66 nests)
Model factors
ka
Deviance
DAICbc
wi
VOR
2
360.71
0.00
0.28
VOR ? monitoring techniquec
3
359.85
1.15
0.16
VOR 9 monitoring techniquec
4
357.90
1.21
0.15
VOR ? precipitationc,d
3
360.29
1.59
0.13
Constant
1
364.63
1.91
0.11
Monitoring technique
2
364.07
3.36
0.05
Precipitationd
2
364.22
3.51
0.05
VOR 9 Precipitationc,d
4
360.28
3.60
0.05
Monitoring technique ? precipitationd
3
363.62
4.92
0.02
Monitoring technique 9 precipitationd
4
362.77
6.09
0.01
a
b
c
k = number of parameters, deviance = -2lnL
Minimum AICc = 364.73
Models with uninformative parameters that were not competitive with the top model (Arnold 2010)
d
Daily precipitation data were from a weather station at Concordia Blosser Municipal Airport
(USW00013984, http://www.ncdc.noaa.gov)
(Rwi = 0.75). Daily survival rates of prairie chicken nests
increased with increasing VOR (b = 0.27, 95 % CL
-0.05, 0.59; Table 2). Precipitation was not supported as
having an important effect on daily nest survival rate
(wi = 0.05; b = 0.05, 95 % CL -0.11, 0.21; Table 2).
Discussion
Female Greater Prairie-Chickens maintained a high incubation constancy of *95 % per day and typically took
two *40-min recesses per day, usually within 2–3 h after
sunrise or before sunset. Our results are consistent with
past studies of grouse with uniparental incubation by
females where nest attendance consists of high incubation
constancy C90 %, and few recesses per day (2–7), with
most breaks taken at sunrise and sunset. The same pattern
of incubation rhythm has been observed among multiple
species in different habitats; including prairie grouse
(Coates and Delehanty 2008; this study), forest grouse
(Pulliainen 1971; McCourt et al. 1973; Maxson 1977;
Summers et al. 2009), and arctic and alpine ptarmigan
(Giesen and Braun 1979; Erikstad 1986; Wiebe and Martin
1997). We discuss our results in the context of potential
selection pressures acting on incubation behavior related to
predation risk versus the physiological needs of the incubating female and the eggs.
Female grouse sustain long stretches of incubation
punctuated by relatively short recess bouts, despite being
uniparental incubators. In contrast, shorebirds and waterfowl with uniparental incubation typically exhibit lower
incubation constancy (*70–85 %), and take longer or
more frequent recesses (1–12 per day; Cartar and Montgomerie 1985; Afton and Paulus 1992; Smith et al. 2012a,
b). High incubation constancy speeds up embryonic
development and reduces the incubation period, minimizing physiological costs and the duration of predation risk
(Thompson and Raveling 1987; Tombre and Erikstad 1996;
Wiebe and Martin 1997; Samelius and Alisauskas 2001;
Hepp et al. 2006; Carter et al. 2014). Other advantages of
high incubation constancy include fewer trips to and from
the nest, which may attract predators to the eggs, and lower
thermoregulatory costs of rewarming eggs after recesses
(Drent 1975; Ghalambor and Martin 2002). Thus, high
incubation constancy reduces predation risk to parents and
offspring while reducing physiological costs for the parent
(Erikstad 1986; Cartar and Montgomerie 1985; Ghalambor
and Martin 2002; Coates and Delehanty 2008).
Duration and timing of recesses can involve tradeoffs
between the survival of attending parents and offspring
(Erikstad 1986; Wiebe and Martin 1997; Davis and Holmes
2012; Pietz et al. 2012; Reidy and Thompson 2012). If
incubating females adjusted recess timing to avoid predator
activity, we predicted recesses to occur at midday when
mesocarnivores were least active. Instead, we observed
prairie chickens taking most recesses near sunrise and
sunset. Grouse populations under high levels of predation
pressure from avian and mammalian predators exhibit the
same bimodal pattern of recess timing, but previous
researchers have attributed the pattern to different ecological and physiological drivers. Bimodal recess patterns
for Greater Sage-Grouse (Centrocercus urophasianus) in
123
J Ornithol
Nevada and Willow Ptarmigan (Lagopus lagopus) in
Norway were explained as responses to predation risk from
corvid predators (Erikstad 1986; Coates and Delehanty
2008). Greater Prairie-Chickens in Kansas and Whitetailed Ptarmigan (Lagopus leucura) in Colorado also
exhibit a bimodal distribution of recess timing, but most
clutch loss occurred during overnight hours from mesocarnivore predators (Wiebe and Martin 1997; this study).
A bimodal pattern of recess timing may not be driven
primarily by predation pressure, but by physiological needs
of the incubating female. Female grouse may maintain
steady state metabolism by taking recesses at dawn after
fasting overnight, and recesses at dusk to obtain energy
reserves for overnight hours (Wiebe and Martin 1997).
Moreover, female grouse store waste products during
incubation, defecate infrequently, and produce large
‘clocker’ droppings that are usually deposited away from
the nest (Watson 1972; Keppie and Herzog 1978; Steen
et al. 1985). Patterns of nest attendance appear to be conserved in grouse and may indicate that females may be
prioritizing their own physiological needs and residual
reproductive value over current nest survival (Tulp and
Schekkerman 2006). In our study, incubation behavior was
not an important driver of variation in nest survival. The
apparent tendency of females to prioritize their own needs
and future reproductive value may represent an optimal
tradeoff between competing needs of current vs. future
reproductive value.
We found no evidence for negative effects of video
surveillance on nest survival, similar to past work
(Richardson et al. 2009; Powell et al. 2012). If anything,
survival rates for video nests tended to be higher than those
for unmanipulated nests in our study, consistent with
neophobia among mammalian predators (Richardson et al.
2009). A recent study on Greater Sage-Grouse found no
evidence for negative effects of monitoring on daily nest
survival when the female was not flushed, but abandonment due to observer-induced flushing resulted in artificially depressed nest survival rates (Gibson et al. 2015). In
our study, nest survival was higher when females took
fewer recesses per day, but variation in nest attendance
behaviors had a minimal effect on nest survival compared
to vegetative cover, in part because we observed little
variation for both incubation constancy and number of
recesses per day. High quality nesting habitat is a limiting
resource for female prairie chickens in nesting tallgrass
prairie, because most rangelands are privately owned and
intensively managed for cattle production (McNew et al.
2014, 2015, Sandercock et al. 2015). Intensive application
123
of fire and grazing reduces vegetative cover, and the effect
of vegetative cover on nest survival outweighs other
potentially contributing factors (Matthews et al. 2013;
Hovick et al. 2014; McNew et al. 2014, 2015). As video
surveillance studies become more common, we will continue to gain insights into site- and species-specific drivers
of nest attendance behaviors and their effect on demographic rates. Future research should investigate the
tradeoffs between adult and offspring survival, and the
possible interactions between changes in habitat quality,
inclement weather, and predation pressure on incubation
behavior and daily nest survival of grouse populations. The
study design should include appropriate controls to ensure
that camera methods are not negatively affecting incubation behavior or nest survival.
Acknowledgments We thank the many field technicians who
helped with data collection for our project and A. Ricketts for
assistance with predator identification. We especially thank S.
Richards, D. Weaver, L. Perry, and other landowners in Kansas for
allowing us access to private property. All capture, marking, and
tracking activities were performed under institutional animal care and
use protocols approved by Kansas State University (IACUC protocol
2781) and state wildlife research permits (SC-082-2010, SC-0112011). Research funding and equipment were provided by a consortium of federal and state wildlife agencies, conservation groups, and
wind energy partners under the National Wind Coordinating Collaborative (NWCC) including the Department of Energy, National
Renewable Energies Laboratory, U.S. Fish and Wildlife Service,
Kansas Department of Wildlife, Parks, and Tourism, Kansas Cooperative Fish and Wildlife Research Unit, National Fish and Wildlife
Foundation, Kansas and Oklahoma chapters of The Nature Conservancy, BP Alternative Energy, FPL Energy, Horizon Wind Energy,
and Iberdrola Renewables.
Compliance with ethical standards
Conflict of interest
of interest.
The authors declare that they have no conflict
Ethical approval All applicable international, national, and/or
institutional guidelines for the care and use of animals were followed.
All procedures performed in studies involving animals were in
accordance with the ethical standards of the institution or practice at
which the studies were conducted.
Appendix 1
Equipment used to video-monitor nests of Greater Prairie
Chickens in northcentral Kansas, 2010 and 2011. AC
alternating current, BNC Bayonet Neill-Concelman, DC
direct current, DVR digital video recorder, LED lightemitting diode, RCA Radio Corporation of America, TRS
tip, ring, sleeve.
J Ornithol
Appendix 2
Predation attempts at Greater Prairie-Chicken nests monitored by video cameras in north central Kansas, 2010 and
2011.
Year
Time
(24 h)
2011
00:05
2011
2010
2011
2010
2011
2011
Nest age
(days)a
Predatorb
Outcomec
Predatorb
Outcomec
9
Bullsnake
Total clutch loss
13
Bullsnake
Total clutch loss
Unknown
mammal
Total clutch loss
Coyote
Total clutch loss
Year
Time
(24 h)
Nest age
(days)a
2011
18:41
2010
18:49
2010
20:02
18
2011
21:08
1
2011
21:48
14
Bullsnake
Total clutch loss
Coyote
Total clutch loss
Bullsnake
Partial clutch
loss
Total clutch loss
17
Coyote
Total clutch loss
2011
21:55
22
00:21
2
Skunk
Total clutch loss
2010
21:56
9
01:02
21
coyote
Total clutch loss
01:22
0
Skunk
Total clutch loss
2010
22:02
19
Badger
01:41
23
Skunk
Total clutch loss
2011
22:10
14
Coyote
Total clutch loss
02:39
4:14
14
1
Badger
Opossum
Total clutch loss
Partial clutch
loss
2011
22:58
22
Skunk
Total clutch loss
2011
04:48
14
2011
05:23
10
Coyote
Total clutch loss
2011
05:33
4
Coyote
Total clutch loss
2011
9:51
14
Ground
squirrel
Unsuccessful
attempt
Coyote
Total clutch loss
Bullsnake
Rattlesnake
Total clutch loss
Unsuccessful
attempt
2011
10:26
3
2011
2011
12:47
15:29
17
7
Coyote
Total clutch loss
a
Number of days since female initiated incubation
b
Predators included: massasauga rattlesnake (Sistrurus catenatus),
bullsnake (Pituophis catenifer), Virginia opossum (Didelphis virginiana), thirteen-lined ground squirrel (Ictidomys tridecemlineatus),
coyote (Canis latrans), American badger (Taxidea taxus), striped
skunk (Mephitis mephitis)
c
Total clutch loss = predator completely or partially consumed a
female or eggs from a nest that subsequently became inactive; partial
clutch loss = predator consumed a portion of eggs from a nest that
remained active following the predation event; unsuccessful
attempt = predator unsuccessfully attempted to consume eggs
123
J Ornithol
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