Site by Bennett Web & Design Co.
2012 SOUTHEASTERN NATURALIST 11(2):319–330
Breeding Biology, Behavior, and Ecology of Setophaga
cerulea in the Cumberland Mountains, Tennessee
Than J. Boves1,2,* and David A. Buehler1
Abstract - Setophaga cerulea (Cerulean Warbler) is one of the fastest declining avian
species in the United States, and its conservation has been hampered by a lack of basic
biological information. Here we describe basic breeding biology and behavior and report
incidental observations of scientific interest from three years of research on Cerulean
Warblers in the Cumberland Mountains of eastern Tennessee. We located and monitored
241 nests and banded 83 Cerulean Warblers from 2008–2010. We documented mating
strategies, timing and plasticity of reproduction, details of nest construction and maintenance,
parental behavior, predation of juveniles, post-fledging behavior, interspecific
interactions, female weight, and a longevity record. Many of these observations have
not been formally recorded and add new dimensions to our understanding of Cerulean
Warbler biology, ecology, and life history.
Setophaga cerulea Wilson (Cerulean Warbler) is one of the fastest declining
avian species in the United States (Ziolkowski et al. 2010). Despite their vulnerability,
Cerulean Warblers are also one of the least studied wood warbler species
(family Parulidae) in North America. The lack of information on this species is
largely related to difficulties associated with locating and monitoring nests, and
capturing these residents of mature forest canopies (Hamel et al. 2004). The paucity
of basic biological information has also made it difficult to generate effective
conservation recommendations. For these reasons, there has been a concerted effort
over the past decade to increase our understanding of Cerulean Warblers across
their eastern North American range (Bakermans and Rodewald 2009, Buehler et al.
2008, Jones et al. 2001, Robbins et al. 2009).
To further improve our understanding of this species in the core of its breeding
range, we recorded details of the breeding biology of Cerulean Warblers from 2008–
2010 in the southern Appalachian Mountains. Here we present basic biological data
from this vital portion of the species’ range, particularly concerning reproductive
timing and behavior, and discuss its significance. When possible, we compare our
data with those from other parts of the species’ range. In addition, we describe incidental
observations of Cerulean Warbler behavior and ecology. Many of these
phenomena have not been formally documented (or have been documented only
in a limited manner), and while some are likely anomalous, others may represent
natural geographic variation, behavioral plasticity, or simply behavior that we have
yet to record. In any case, the information we present here increases our knowledge
of Cerulean Warblers and should provide impetus for future research designed to
1Department of Forestry, Wildlife, and Fisheries, University of Tennessee, Knoxville, TN
37996. 2Current address - Department of Natural Resources and Environmental Sciences,
University of Illinois, Urbana, IL 61801. *Corresponding author - email@example.com.
320 Southeastern Naturalist Vol. 11, No. 2
answer specific ecological questions as well as improve our ability to conserve this
declining species, particularly in the southern Appalachians.
We studied Cerulean Warblers on two heavily-forested sites located in the
North Cumberland Wildlife Management Area, Campbell County, TN (36°12'N,
84°16'W and 36°21'N, 84°18'W; Fig. 1). Sites were located ca. 10 km apart
and each site consisted of ≈30 ha of forest harvested in the fall of 2006 (using
shelterwood or single-tree selection methods) and ≈50 ha of unmanaged forest
(70–100 yrs old) for a total of ≈80 ha. Forest cover on the surrounding landscape
was high, ≈80% within a 10-km radius, and elevation varied from 760–940 m at
one site and 600–725 m at the other. Both sites were predominantly of mixedmesophytic
forest type and tree composition was mainly Quercus spp. (oak),
Acer spp. (maple), Carya spp. (hickory), and Liriodendron tulipifera L. (Tulip
Poplar). The Cumberland Mountains sustain Cerulean Warblers at some of their
highest breeding densities in the world (Buehler et al. 2006), and mean density of
warblers on our sites in 2010 was 0.76 territories/ha (T.J. Boves, unpubl. data).
The field-sites were located ≈30 km north of the nearest National Weather Service
station (at Oak Ridge, TN) from which we obtained climate data.
Figure 1. Map depicting North Cumberland Wildlife Management Area (NCWMA; star
on map), the location of our field sites.
2012 T.J. Boves and D.A. Buehler 321
From late April to July 2008–2010, we used information gathered from
spot-mapping efforts (see Boves 2011 for more detail) to systematically search
for, and intensively monitor, Cerulean Warbler nests. We found the majority
of nests by first locating females, visually or aurally, within a territory, and
subsequently observing behavioral cues indicative of breeding. These cues included
birds peeling bark off vines, collecting silk, or vocalizing on or near the
nest; the most useful vocalizations were the “zeet” or “zzee” contact and flight
calls described by Woodward (1997) and Rogers (2006). To a lesser extent, we
used male behavior, such as whisper-singing or mate-feeding, to aid in locating
nests. Once we located a nest, we used spotting scopes equipped with 20–60x
magnification eyepieces to monitor nests for 30–45 min every 1–2 d. As Cerulean
Warbler nests may be abandoned before completion, and because we
were unable to examine the contents of nests due to their height, we considered
nests “active” only if incubation had begun (14% of nests we located never
became active). We considered nests that fledged ≥1 Cerulean Warbler young
to be successful. When we discovered a previously constructed nest to be missing,
we searched the ground in the immediate area and collected all fully intact
nests. We identified the materials used in construction and measured nest dimensions
using digital calipers.
We compared reproductive characteristics among years using one-way
ANOVAs (α = 0.05) after examining variables for normality and equality of variances
and transforming variables when appropriate, or using the non-parametric
Kruskal-Wallis test. We performed all statistical analyses using NCSS statistical
software (Version 7.1.19, Kaysville, UT). To potentially explain shifts in reproductive
timing, we compared spring temperatures among years of study (and to
62-yr norms) by calculating cumulative cooling degree-days for several time
n — Σ( Ti - 18.3 °C),
i = 1 April
where T is temperature and all values of (T̅i - 18.3 °C) < 0 were discarded., We compared
the period from 1 April–10 May for nest initiation timing and 1 April–1 June
for fledging. From 1949–2010, the average cumulative cooling degree-days that
occurred between 1 April and 10 May at the Oak Ridge station was 25.5; between 1
April and 1 June, the average cumulative cooling degree-days was 78.9.
We captured and banded Cerulean Warblers by erecting mist nets within territories,
broadcasting territorial songs and various call notes, and displaying a
decoy of an intruding male Cerulean Warbler to lure birds down from the canopy.
Once captured, each individual was fitted with a unique combination of plastic
colored leg bands, which allowed us to identify individuals in the field without
recapture. We recorded mass with a digital scale, wing chord with a straight ruler,
and age as either second-year (SY) or after-second year (ASY) based on plumage
and molt limits (Pyle 1997).
322 Southeastern Naturalist Vol. 11, No. 2
Results and Discussion
We located and monitored 241 nests (208 active) and banded 78 male (28%
SY, 72% ASY) and five female Cerulean Warblers over the course of this threeyear
study. Despite the difficulties associated with finding nests of this species,
we were able to locate nests on >70% of territories over this time period.
The warblers appeared to be predominantly socially monogamous on our field
sites, which is typical of the species (Hamel 2000). Bigamous males, defined
here as individuals associated with >1 nest simultaneously, were reported previously
in Ontario (≈10% of males; Barg et al. 2006), and we observed six cases of
bigamy (consisting of five individuals, 7% of our banded males): three in 2008,
one in 2009, and two in 2010. One male (oldest Cerulean Warbler on record, see
below) was bigamous during two breeding seasons (2008, 2009). The true prevalence
of bigamy was likely greater than this as we were unable to locate every
nest associated with all banded males.
Nest-site selection behavior
Females selected their nest sites with very little assistance from males, which
differs from other portions of their range where males are regularly involved
in nest site selection (Hamel 2000, Oliarnyk and Robertson 1996). On our field
sites, females typically independently selected a nest site by inspecting many
locations where two or more branches or peripheral twigs met (hereafter referred
to as forks) within their social mate’s territory. They evaluated potential nest
sites by crouching down and rotating their body in both directions (presumably
to assess the potential fit of a nest at that fork). This action was often performed
several times at many potential nest locations; we observed some females assess
>10 tree forks over several days before an appropriate nest site was decided upon.
As females selected nest sites and constructed nests, males would often sing at
very low volumes nearby (whisper-singing). On one occasion, we observed a
male perched at a selected nest site whisper-singing repeatedly for 15 min as the
female constructed her nest around him. While rare on our sites, we observed four
instances of males directly aiding in the selection of a nest site. In these cases,
males accompanied, and sometimes led, females to potential forks, testing sites
in a similar manner and whisper-singing often.
Once a nest location was selected, females typically built the nest unaided by
the male; however, we observed three males gather spider (or caterpillar) silk and
help construct the primary layers of the nest (but having no further involvement).
One was an initial nesting attempt that was successful, another was a second
nesting attempt that failed during incubation, and the last was a third nesting attempt
that was also successful. Male assistance in nest construction appears to be
uncommon, but it may be adaptive for both sexes to participate in the search for
silk, as it is a potentially limited resource.
Timing of nest initiation
Not accounting for initial vs. subsequent nesting attempts, the mean date that
nest construction began was 12 May. The earliest nest initiation date was 26 April
2012 T.J. Boves and D.A. Buehler 323
(in 2010), and the latest initiation date was 14 Jun (in 2010), a period spanning 50
days. When known re-nesting attempts were excluded, mean nest initiation date
was 10 May (Table 1). This timing is more than a week earlier than the earliest
nest initiation dates for initial nests in Ontario (18 May to 24 May; Oliarnyk and
Robertson 1996). Nest construction took 5.44 ± 0.19 d (mean ± 1 SE; Table 1)
with a range of 2–11 d (n = 62, based only on nests that we believe we found
on the first day of construction and where incubation eventually occurred). Nest
initiation dates differed among years (using log-transformed Julian dates, initial
nests only: F2,135 = 3.64, P = 0.03; Table 1) as did days required to build nests
(using square-root of construction days: F2,60 = 4.10, P = 0.02; Table 1). Initial
nests were built earlier in 2010 than in 2008 (post-hoc Tukey-Kramer multiple
comparisons test: P < 0.05) and faster in 2010 than in 2009 (post-hoc Tukey-
Kramer multiple comparisons test: P < 0.05).
Annual variation in reproductive timing was potentially attributable to
variability among years in weather patterns and associated leaf and insect phenology
(e.g., Visser et al. 2006). Cumulative cooling degree-days from 1 April–10
May (mean date of nest initiation across all years) increased annually. There
were 23.3 cooling degree-days during that time period in 2008 (vs. a 62-yr norm
of 25.5), 27.8 in 2009 (+19% over 2008), and 46.2 in 2010 (+98% over 2008;
NOAA 2011). Moreover, the number of cooling degree-days (46.2) that had already
occurred on 10 May in 2010 did not occur until 30 May in 2008, and 23
May in 2009. Thus, the spring heat wave of 2010 caused leaf expansion to occur
noticeably earlier and faster (T.J. Boves, pers. observ.), which likely affected
peak insect availability. We do not know if this warm spring caused birds to arrive
on breeding grounds earlier or if they arrived on similar dates and the presence
of nest-concealing foliage and large quantities of food resources induced females
to build nests immediately. Either way, behavioral plasticity in the timing of nest
initiation by Cerulean Warblers was evident.
Table 1. Summary of Cerulean Warbler reproductive timing and breeding parameters in the Cumberland
Mountains of eastern Tennessee, 2008 – 2010. Number of nests are indicated in parentheses.
Parameter 2008 2009 2010 All
Nests found 68 88 85 241
Mean date of initiation; 12 May (40) 9 May (48) 7 May (49) 10 May (137)
Days of construction ± SE 5.80 ± 0.24 6.13 ± 0.53 4.94 ± 0.22 5.44 ± 0.19
(15) (15) (32) (62)
Days in incubation period ± SE 11.68 ± 0.19 11.96 ± 0.20 12.21 ± 0.15 12.00 ± 0.10
(28) (25) (47) (100)
Days in nestling period ± SE 10.66 ± 0.15 10.64 ± 0.16 10.53 ± 0.12 10.59 ± 0.08
(32) (28) (52) (112)
Mean date of fledging 13 June (42) 9 June (36) 7 June (55) 9 June (133)
Nest success 0.67 (60) 0.55 (67) 0.68 (81) 0.63 (208)
Young/successful nest ± SE 3.25 ± 0.16 3.24 ± 0.10 3.35 ± 0.11 3.29 ± 0.07
(28) (34) (49) (111)
324 Southeastern Naturalist Vol. 11, No. 2
Nest dimensions and materials
We collected 10 fully intact nests that fell to the ground and recorded their
dimensions. External cup diameter was 6.93 ± 0.12 cm, internal cup diameter was
4.92 ± 0.08 cm, external cup depth was 4.58 ± 0.21 cm, and internal cup depth
was 3.03 ± 0.16 cm. These dimensions were similar to those reported from five
nests in Ontario (Oliarnyk and Robertson 1996), except for external cup depth,
which was markedly greater in our study (3.3 ± 0.7 cm in Ontario). Larger nests
on our study sites may be related to nest height. Nests were, on average, located
≈10 m higher above the ground in the Cumberlands (Boves 2011), increasing the
likelihood that wind could affect nest stability and increasing the need for more
substantial nests. The difference in nest size may also be related to available
nest materials (e.g., stronger spider silk or more grapevines available in TN),
predators (e.g., visual predators may be less of a threat in TN), ectoparasites, or
climate differences (see Crossman et al. 2011), but larger sample sizes are needed
to speculate further.
The most common, and identifiable, materials used in nest construction were
typical of the species across their range and included spider or caterpillar silk,
grapevine bark, other fine plant fibers, and the occasional lichen covering the
outside of the nest. We also found oak and hickory catkins incorporated in two
nests, which is the first report of these materials being used.
Incubation and nestling period
Once a nest was completed and eggs were laid, females incubated exclusively
(also typical of the species). The mean period of incubation for eggs that survived
to hatching was 12 d (range = 9–15 d; Table 1), with no statistical difference
among years (Kruskal-Wallis test: χ2
2 = 4.53, P = 0.10). In relatively benign
weather conditions (i.e., no rain, little wind), females spent approximately 30-
min periods incubating followed by 5–10 min of foraging; they repeated this
throughout the incubation period. Nest and egg maintenance was performed by
the female alone and included removal of arthropods from the outside of the
nest and improvement of the structural integrity of the nest cup by adding or
re-weaving plant material. We observed males providing food to incubating females
at least once during incubation at 13 nests (7% of the nests [n = 183] that
we monitored in incubation stage). This proportion is much lower than the 35%
prevalence of this behavior in Ontario (Barg et al. 2006), a difference that may
be related to higher temperatures and/or greater food availability in the southern
portion of their range, as females can leave eggs unattended for longer periods of
time and prey may be more abundant.
We were unable to view nestlings when first hatched, but we believe we were
able to determine hatching date with accuracy based on cues provided by parents
including feeding, rapid probing by the female (see below), and restlessness of the
female when initially brooding. Brooding was performed almost solely by females;
however, we observed one male brood 3-d old nestlings for 15 min on 25 June
2009, representing the first reported case of biparental brooding by the species.
This male was not observed assisting with nest construction. Females continued
to perform nest maintenance during the nestling period. During this stage, maintenance
included a behavior termed “rapid probing” or “tremble thrusting” (Greeney
2012 T.J. Boves and D.A. Buehler 325
et al. 2008, Haftorn 1994). This behavior, known mainly from resident Neotropical
species, consists of the female probing her beak into the nest rapidly with a motion
reminiscent of a sewing machine. This behavior was observed at 71% of nests
that we monitored during the nestling period (n = 168 nests), an unexpectedly high
prevalence given that it had yet to be reported in this species. We speculate that this
behavior was used to remove ectoparasites from nestlings or the bottom of the nest;
the true function of the behavior is still unknown.
Provisioning of nestlings and fecal sac removal were almost always biparental;
however, we monitored three nests (2% of successful nests) where males did
not provide any care for nestlings. As we were unable to conclusively identify
the males associated with these nests, it was not possible to determine if they
provisioned young at any additional nest(s). Two young fledged from one of these
nests, and three fledged from each of the other two despite the putative handicap
of uniparental care. We did not document any failed nests which lacked biparental
care, although this may be because some nests failed before we were able to
determine the parental state. Nestlings which survived to fledge remained in the
nest for ≈10.5 d (range = 8–13 d; Table 1), with no statistical difference among
years (Kruskal-Wallis test: χ2
2 = 2.59, P = 0.27).
Nest failure and predation
Of 76 failed nests, 53% failed during the incubation period (vs. 47% as nestlings),
which is equal to the proportion of time offspring would spend in each
stage at a successful nest. This suggests a diversity of predators (or other causes)
were responsible for nest failures. Nests which failed during the nestling period
did so when the nestlings were 5.00 ± 0.39 d old (range = 0.5–9 d; n = 32 nests).
We were able to assign a cause of failure to 16 nests. While predation is considered
to be the primary cause of most passerine nest failure (Martin 1993), we
directly observed only four predation events (only one of which caused complete
nest failure). Two cases consisted of egg predation, one of nestling predation, and
one of early fledgling predation. Cyanocitta cristata L. (Blue Jay) were responsible
for both cases of egg predation (both on 19 May 2010, one was a partial
brood reduction) and nestling predation (26 May 2010, partial brood reduction).
Tamias striatis L. (Eastern Chipmunk) was recorded on video depredating a
nestling (8 d old) on the ground that fell out of a nest early on 26 May 2010. Additionally,
we observed a chipmunk force-fledge four nestlings from a nest that
was located 15 m above the ground on 2 June 2008. In this case, the response
by the avian community after the young fledged from the nest was interesting as
well. Presumably instigated by the alarm calls given by the Cerulean Warbler parents,
nine other species of birds chipped, dove at, and generally antagonized the
Chipmunk as it sat still next to the empty nest for >2 hrs. Cerulean Warbler nest
and post-fledging predators are still poorly documented, and it will require 24-hr
video monitoring of nests and intensive fledgling studies to better understand and
quantify this important selective pressure.
In addition to the nests where we observed depredation events, we inferred or
witnessed the cause of failure for 15 other nests. Six nests likely failed because
of unknown predators (based on structural damage to the nest in the tree; 9% of
failed nests), five likely failed from disease or starvation (based on increasingly
326 Southeastern Naturalist Vol. 11, No. 2
lethargic nestling behavior, flies at nest, and parents attempting, but unable, to
feed nestlings; 7% of failed nests), two from weather-related causes (based on
nests/limbs found on ground after severe weather events; 3% of failed nests),
one from brood parasitism by Molothrus ater Boddaert (Brown-headed Cowbird)
(based on presence of Cowbird fledglings observed in nest; 1% of failed
nests), and one from conspecific egg destruction (see Boves et al. 2011; 1% of
failed nests). All other failed nests (80% of total failed nests) were abandoned
for unknown reasons. As these nests were abandoned suddenly, it is likely that
predation was the cause of failure, but cowbird parasitism cannot be ruled out as
a potential cause for sudden abandonment (Robinson et al. 1995).
Nest success and fledging
Nest success across all years was 63%; it varied from 55% in 2009 to 68% in
2010 (Table 1). Mayfield nest success (based on complete nesting period of 25 d)
was only slightly lower at 59% and there was a marginal statistical difference
among years (Program CONTRAST: χ2
2 = 4.88, P = 0.09). Cerulean Warblers
fledged 3.29 young per successful nest (based only on nests where we could
make an accurate count, range = 1–5; Table 1), and we detected no difference in
number of young produced/nest among years (Kruskal-Wallis test: χ2
2 = 1.15, P =
0.56). When compared with reproductive output in other portions of its range,
these values are exceptionally high (Buehler et al. 2008) and further support the
importance of the Cumberland Mountains for the continued persistence of the
global population (Buehler et al. 2006).
The mean date of fledging for all nests (including re-nesting attempts) was
9 June. The earliest date of fledging was 26 May (2010), and the latest date we
documented fledging was 14 July (2010). Similar to nest initiation, fledging date
also varied among years (using log-transformed Julian dates; F2,130 = 5.18, P =
0.007). Nests fledged earlier during the 2010 breeding season than in 2008 (posthoc
Tukey-Kramer multiple comparisons test: P < 0.05). Climate variability
(particularly an extremely warm spring in 2010) was also likely responsible for
this temporal pattern. For the period 1 April–1 June, 58.9 cooling degree-days
occurred in 2008 (vs. a 62-yr norm of 78.9), 81.9 occurred in 2009 (+39% over
2008), and 130.2 occurred in 2010 (121% over 2008; NOAA 2011). While the
earlier fledging (and nest initiation) dates did not appear to be proportional to
the extreme increase in cooling degree-days, birds did appear to adjust their
reproductive timing, at least to some extent, to match climatic, and associated
Most nests on our field sites produced 3 or 4 young; however, we observed 5
young fledge from a single nest on 26 June 2008. To our knowledge, this was the
first case of a Cerulean Warbler nest producing 5 fledglings. Cerulean Warblers
are single-brooded and often fledge only 2 or 3 young per successful nest across
their range (Buehler et al. 2008), so the capacity to produce 5 young represents
plasticity of a vital life-history trait. Factors which regularly limit Cerulean Warbler
clutch size to <5 could be related to food or nutrients (e.g., calcium; Patten
2007), predation pressures (Lima 1987), or thermoregulatory costs, which may
be greater for canopy nesters than ground-nesting species (Martin 1988). We did
not record any instances of double-brooding.
2012 T.J. Boves and D.A. Buehler 327
Post-fledging behavior and care
We did not make specific attempts to follow family groups once nestlings
fledged; however, we made several incidental observations regarding postfl
edging behavior. We observed a banded after-third-year male foraging with two
hatch-year (HY) birds on 7 July 2009, 30 d after the nest he was associated with
had fledged young. We cannot be certain that these juveniles were his offspring,
but the three birds remained as a cohesive feeding flock for >40 min (after which
we lost sight of them). Very little is known about Cerulean Warbler post-fledging
care or brood division, and it is unknown how long parents routinely stay with
fledglings. This observation suggests that the post-fledgling period of care may
be longer than previously assumed. However, given that they typically raise only
a single brood, this increased post-fledging period of care may be expected. More
research is required on post-fledging behavior.
We observed a HY Cerulean Warbler monitoring the activity at a nest late in
the breeding season on 10 July 2008. The young bird perched within 2 m of the
nest as the parents fed nestlings for ≈5 min. The sex of this bird and its relation to
the parents were unknown. We do know that it was not an offspring of the adult
female, as she had failed in her previous two nesting attempts of the season. The
parents appeared to be unconcerned by the presence of this individual, which was
unexpected given their normal responsiveness to intruders near their nests.
We video-recorded ≥3 HY Cerulean Warblers performing rambling, low-volume,
buzzy subsongs on 10 July 2008. We do not know when these birds actually
hatched, but the very earliest would have been at the end of May, suggesting that
these birds were no older than 45 d, and likely not much older than 30 d of age.
Typically, passerines do not begin performing subsongs until testosterone induces
them to do so during their first spring (Catchpole and Slater 2008); however, many
exceptions have been documented (e.g., Bradley 1980, Johnson et al. 2002). There
are no previous reports of Cerulean Warblers performing subsongs.
We documented interspecific interactions between Cerulean Warblers and other
members of the avian community. Multiple species engaged in, or attempted to
engage in, kleptoparasitism of nesting material from Cerulean Warbler nests. The
intruding species, the stage of the nest, and date of the events were: Bombycilla
cedrorum Viellot (Cedar Waxwing), building, 3 June 2008, and nestling, 6 June
2008; Piranga olivacea Gmelin (Scarlet Tanager), building, 4 May 2010, and
nestling, 25 May 2010; Vireo olivaceus L. (Red-eyed Vireo), nestling, 30 May
2009; Setophaga virens Gmelin (Black-throated Green Warbler) egg laying (or
failed nest), 23 May 2009; and Setophaga ruticilla L. (American Redstart; hereafter
Redstart), see below. Red-eyed Vireos and American Redstarts have been
identified as kleptoparasites of Cerulean Warbler nest material previously (Jones
et al. 2007), but the other species are newly reported.
We observed multiple cases of Redstarts acting antagonistically towards
Cerulean Warblers. Interactions typically consisted of male and female Redstarts
chasing and scolding male and female Cerulean Warblers for unknown
reasons. There were three cases where Redstarts’ aggressive behavior may
have played a role in abandonment of a nest. In one case, a pair of neighboring
328 Southeastern Naturalist Vol. 11, No. 2
Redstarts incessantly antagonized a female Cerulean Warbler that was incubating
eggs (both while she incubated and while she foraged near the nest). Then
during a routine nest check on 2 June 2008, a female Redstart was observed
sitting in the (former) Cerulean Warbler nest. The Redstarts did not continue
to use the nest, but the Cerulean Warbler parents never returned to it either.
On 10 May 2010, a female Redstart took over a nest built by a female Cerulean
Warbler whom we believed to be in the egg-laying stage. The Redstart
proceeded to (presumably) incubate eggs of unknown parentage at this nest
(15 May 2010). The Redstart eventually abandoned this nest. Finally, a female
Redstart stole nesting material from an abandoned Cerulean Warbler nest on
17 May 2009. Redstarts have been identified as general antagonists towards
Cerulean Warblers in other parts of their range as well (Hamel 2000). These
observations, combined with the complete absence of evidence of reverse
kleptoparasitism on our sites (i.e., Cerulean Warblers stealing other species’
nest material), indicate that Cerulean Warblers may be subordinate members
of avian communities, and nesting material and nesting sites, such as animal
silk or ideal tree branches/forks, may be limited resources for multiple species.
Jones et al. (2007) did report a female Cerulean Warbler stealing material from
a nest built by a Polioptila caerulea L. (Blue-gray Gnatcatcher), which in parts
of the species’ range is one of the few canopy-dwelling avian species that are
smaller than Cerulean Warblers and which these warblers may maintain dominance
over (but this species did not occur on our study sites).
In another instance, a female Black-throated Green Warbler and Cerulean
Warbler both were adding material to the same fork/nest location for >3 hours on
29 May 2010. They appeared to have just started the building process that day;
only a spider silk base and a small amount of plant fiber were present. By the
next day, both birds had abandoned the nest site, but the female Cerulean Warbler
returned several times to salvage some of the spider silk for a new nest.
Female mass in breeding season
We captured five female Cerulean Warblers during the spring of 2010, all
of which were very heavy (compared to previous reports and to males on our
study areas). Hamel (2000) reported males to normally weigh more than females
during migration in southern Mississippi (8.35 ± 0.16 g for males vs.
8.19 ± 0.19 g for females) and Pennsylvania (9.28 ± 0.09 g for males vs. 8.83
± 0.10 g for females). Curson et al. (1994) reported weights of 8.4–10.2 g,
without differentiating between sexes. At our study areas, however, banded
males weighed 9.37 ± 0.04 g (n = 70, range = 8.6–10.4 g) and these five females
weighed 11.08 ± 0.38 g (range = 10.2–12.4 g). At least four of the
females appeared to be in the process of egg production, which may account
for a portion of the ≈18% greater mass (vs. males). The average weight of a
Cerulean Warbler egg is currently unknown; however, if it is similar to the
range of egg mass (1.2–1.7 g) of a congeneric, Setophaga petechia L. (Yellow
Warbler; Guigueno and Sealy 2009), females would still weigh more than
males early in the breeding season in the Cumberland Mountains even after
subtracting for the weight of a developing egg.
2012 T.J. Boves and D.A. Buehler 329
On 7 May 2012, we documented a male Cerulean Warbler that was captured
as an ASY bird in 2006 and was therefore ≥8 yrs old in 2012. This represents a
published longevity record for Cerulean Warblers. He occupied the same territory
location each breeding season since capture, was paired with one or more
females (was bigamous during two seasons), and produced at ≥1 successful
nest each season. While an individual of this age is likely unusual, it does show
that Cerulean Warblers at least have the capacity to live relatively long lives in
This research was funded and supported by the University of Tennessee, Department
of Forestry, Wildlife, and Fisheries; the Tennessee Wildlife Resources Agency; the
National Fish and Wildlife Foundation; the US Fish and Wildlife Service; the Nature
Conservancy; and the National Council for Air and Stream Improvement, Inc. We thank
the many field assistants that helped collect this data, particularly N.E. Boves, P.C.
Massey, D. Raybuck, A. Langevin, P. Capobianco, D. Rankin, J. Piispanen, M. Horton,
J. Glagowski, and E. DeHamer. We thank T.A. Beachy for resighting our elder Cerulean
Warbler in 2012. We thank T.B. Wigley and two anonymous reviewers for helpful comments
on an earlier version of this manuscript.
Bakermans, M.H., and A.D. Rodewald. 2009. Think globally, manage locally: The importance
of steady-state forest features for a declining songbird. Forest Ecology and
Barg, J.J., J. Jones, M.K. Girvan, and R.J. Robertson. 2006. Within-pair interactions and
parental behavior of Cerulean Warblers breeding in eastern Ontario. Wilson Journal
of Ornithology 118:316–325.
Boves, T.J. 2011. Multiple responses by Cerulean Warblers to experimental forest disturbance
in the Appalachian Mountains. Ph.D. Dissertation. University of Tennessee,
Boves, T.J., D.A. Buehler, and N.E. Boves. 2011. Conspecific egg destruction by a female
Cerulean Warbler. Wilson Journal of Ornithology 123:401–403.
Bradley, R.A. 1980. Vocal and territorial behavior in the White-eyed Vireo. Wilson Bulletin
Buehler, D.A., M.J. Welton, and T.A. Beachy. 2006. Predicting Cerulean Warbler habitat
use in the Cumberland Mountains of Tennessee. Journal of Wildlife Management
Buehler, D.A., J.J. Giocomo, J. Jones, P.B. Hamel, C.M. Rogers, T.A. Beachy, D.W.
Varble, C.P. Nicholson, K.L. Roth, J. Barg, R.J. Robertson, J.R. Robb, and K. Islam.
2008. Cerulean Warbler reproduction, survival, and models of population decline.
Journal of Wildlife Management 72:646–653.
Catchpole, C.K. and P.J.B. Slater. 2008. Birdsong: Biological Themes and Variations.
Second Edition. Cambridge University Press, Cambridge, UK. 335 pp.
Crossman, C.A., V.G. Rohwer, and P.R. Martin. 2011. Variation in the structure of bird
nests between northern Manitoba and southeastern Ontario. Plos One 6:1–10.
Curson, J., D. Quinn, and D. Beadle. 1994. Warblers of the Americas: An Identification
Guide. Houghton Mifflin, Boston, MA.
330 Southeastern Naturalist Vol. 11, No. 2
Greeney, H.F., R.C. Dobbs, P.R. Martin, and R.A. Gelis. 2008. The breeding biology of
Grallaria and Grallaricula Antpittas. Journal of Field Ornithology 79:113–129.
Guigueno, M.F., and S.G. Sealy. 2009. Nest sanitation plays a role in egg burial by Yellow
Warblers. Ethology 115:247–256.
Haftorn, S. 1994. The act of tremble-thrusting in tit nests: Performance and possible
functions. Fauna Norvica Series C. Cinclus 17:55–74.
Hamel, P.B. 2000. Cerulean Warbler (Dendroica cerulea). No. 511, In A. Poole (Ed.).
The Birds of North America online. Cornell Laboratory of Ornithology, Ithaca, NY.
Available online at http://bna.birds.cornell.edu/bnai.
Hamel, P.B., D.K. Dawson, and P.D. Keyser. 2004. How we can learn more about the
Cerulean Warbler (Dendroica cerulea). Auk 121:7–14.
Johnson, F., K. Soderstrom, and O. Whitney. 2002. Quantifying song bout production
during Zebra Finch sensory-motor learning suggests a sensitive period for vocal practice.
Behavioural Brain Research 131:57–65.
Jones, J., R.D. DeBruyn, J.J. Barg, and R.J. Robertson. 2001. Assessing the effects of
natural disturbance on a neotropical migrant songbird. Ecology 82:2628–2635.
Jones, K.C., K.L. Roth, K. Islam, P.B. Hamel, and C.G. Smith. 2007. Incidence of nest
material kleptoparasitism involving Cerulean Warblers. Wilson Journal of Ornithology
Lima, S.L. 1987. Clutch size in birds: A predation perspective. Ecology 68:1062–1070.
Martin, T.E. 1988. Processes organizing open-nesting bird assemblages: Competition or
nest-predation? Evolutionary Ecology 2:37–50.
Martin, T.E. 1993. Nest predation and nest sites: New perspectives on old patterns. Bioscience
National Oceanic and Atmospheric Administration (NOAA). 2011. Oak Ridge station.
Available online at http://www.ncdc.noaa.gov/oa/ncdc.html. Accessed 15 May 2011.
Oliarnyk, C.J., and R.J. Robertson. 1996. Breeding behavior and reproductive success of
Cerulean Warblers in southeastern Ontario. Wilson Bulletin 108:673–684.
Patten, M.A. 2007. Geographic variation in calcium and clutch size. Journal of Avian
Pyle, P. 1997. Identification Guide to North American Birds. Slate Creek Press, Bolinas, CA.
Robbins, M.B., A.S. Nyari, M. Papes, and B.W. Benz. 2009. Song rates, mating status,
and territory size of Cerulean Warblers in Missouri Ozark riparian forest. Wilson
Journal of Ornithology 121:283–289.
Robinson, S.K., S.I. Rothstein, M.C. Brittingham, L.C. Petit, and J.A. Grzybowski. 1995.
Ecology and behavior of cowbirds and their impact on host populations. Pp. 428–460,
In T.E. Martin and D.M. Finch (Eds.). Ecology and Management of Neotropical Birds.
Oxford University Press, New York, NY.
Rogers, C.M. 2006. Nesting success and breeding biology of Cerulean Warblers in
Michigan. Wilson Journal of Ornithology 118:145–151.
Visser, M.E., L.J.M. Holleman, and P. Gienapp. 2006. Shifts in caterpillar biomass phenology
due to climate change and its impact on the breeding biology of an insectivorous
bird. Oecologia 147:164–172.
Woodward, R.L. 1997. Characterization and significance of song variation in the Cerulean
Warbler (Dendroica cerulea). M.Sc. Thesis. Queen’s University, Kingston, ON, Canada.
Ziolkowski, D.J., Jr., K.L. Pardieck, and J.R. Sauer. 2010. The 2003–2008 summary of
the North American breeding bird survey. Bird Populations 10:90–109.