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Breeding Biology, Behavior, and Ecology of Setophaga cerulea in the Cumberland Mountains, Tennessee
Than J. Boves and David A. Buehler

Southeastern Naturalist, Volume 11, Issue 2 (2012): 319–330

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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. Introduction 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 - tboves@illinois.edu. 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. Field-site Description 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 Methods 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 periods using: 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. Mating system 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. Year 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) re-nests excluded 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 environmental, fluctuations. 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. Interspecific interactions 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 Longevity record 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 the wild. Acknowledgments 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. 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