Northeastern Naturalist Vol. 21, No. 4 J.R. Wagner and K. Islam 2014 515 2014 NORTHEASTERN NATURALIST 21(4):515–528 Nest-site Selection and Breeding Ecology of the Cerulean Warbler in Southern Indiana Jennifer R. Wagner1,2 and Kamal Islam1,* Abstract - Setophaga cerulea (Cerulean Warbler) has been deemed one of the fastest-declining wood warblers in North America. Recent field studies have focused on understanding breeding requirements across its range and other natural life-history characteristics. During 2010–2011, we conducted a breeding study in Indiana to ascertain reproductive success and document nest-site characteristics associated with 22 nesting locations. We also documented breeding phenology and feeding rates during the nestling stage. Cerulean Warblers had a preference for nesting in Quercus alba (White Oak). Nesting success (30.7%; measured directly through monitoring of nests or presence of fledglings within the territory) was lower than necessary for a source population, but average when compared to other parts of the range. We recommend further inquiry into the fate of the Indiana population, as well as studies to assess reproductive rates and suitable breeding habitats that may exist elsewhere in the Cerulean Warbler’s range. Introduction Setophaga cerulea Wilson (Cerulean Warbler) has experienced the most rapid population declines of any North American wood warbler (Sauer et al. 2011) and is one of the United States’ fastest-declining avian species (Ziolkowski et al. 2010). The Cerulean Warbler is a species of concern nationwide (USFWS 2006) and globally (IUCN 2011). Results from breeding bird surveys conducted from 1966 to 2010 indicated that annual decreases averaged 2.98% (Sauer et al. 2011). As a result of long-term declines, this once common species exists only in a limited portion of its original range (Buehler et al. 2013, Hamel 2000). Therefore, it is crucial to understand the attributes of suitable breeding habitat as well as the life-history characteristics of this species across its range. Some of the potential reasons for Cerulean Warbler declines have been investigated. The Cerulean Warbler exhibits a preference for breeding in large deciduous forest tracts (Buehler et al. 2013, Hamel 2000), and fragmentation of these forests may therefore be a cause of population decreases in this and other avian species (Holmes et al. 1986, Robinson and Wilcove 1994, Wiens 1989). Robbins et al. (1992) suggested that forest management strategies that prevent tree maturation (shorter tree-harvest rotations), and the effects of these activities on nest predation and parasitism may also have negative impacts on Cerulean Warblers. Regardless of the reasons for declines, more data related to breeding habitat throughout the species’ range are needed. 1Department of Biology, Ball State University, 2000 University Drive, Muncie, IN 47306. 2Current address - Department of Fish and Wildlife Conservation, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061. *Corresponding author - kislam@bsu.edu. Manuscript Editor: Rosalind Renfrew Northeastern Naturalist 516 J.R. Wagner and K. Islam 2014 Vol. 21, No. 4 There have been few studies of Cerulean Warbler nesting phenology and certain aspects of nesting ecology. Collection of data in more geographic areas that pertain to these natural history traits is necessary to guide effective conservation of the species. Estimates of reproductive success and the distribution of source and sink populations will allow managers to pinpoint critical breeding areas for this species, as well as assess preferred habitat characteristics that could be used to inform management plan development throughout the Cerulean Warbler’s range. The objectives of this study were to describe and evaluate nest-site selection characteristics in nine study sites in Morgan-Monroe and Yellowwood state forests, IN, and to compare nesting-success rates at our study sites to those in other parts of the Cerulean Warbler’s range. We also sought to determine nesting phenology and provisioning rates of adults. Study Site We conducted this study in 2010–2011, from 1 May to 30 July on nine management units of Morgan-Monroe (9712 ha) and Yellowwood (9439 ha) state forests in Morgan, Monroe, and Brown counties, IN (Fig. 1). In these tracts, forests are continuous, but there is agricultural land-use in some areas (Fig. 1). Since the 1960s, both forests have been harvested using single-tree selection and group-selection practices on 20–30-year cutting cycles (Jenkins and Parker 1998). Currently, the nine management units (size range: 364–405 ha) are being harvested in three replicates each of the following treatments: control (no harvest), even-aged (clearcut and shelterwood), and uneven-aged (patch- and single-tree removal) (Hardwood Ecosystem Experiment 2010). Both forests are within the Brown County Hills ecoregion that is characterized by deeply dissected uplands underlain by siltstone, shale, and limestone (Homoya et al. 1984). Wet-mesic bottomlands in this region are dominated by Acer saccharum Marshall (Sugar Maple), Platanus occidentalis L. (American Sycamore), and Fagus grandifolia Ehrh. (American Beech), and mesic slopes are dominated by Sugar Maple, Liriodendron tulipifera L. (Tulip Poplar), American Beech, and Quercus rubra L. (Northern Red Oak). Dry mesic slopes are dominated by Q. alba L. (White Oak; Jenkins et al. 2004). Methods Territory delineation Study sites (225 ha with a 50-m buffer to the forest edge) consisting of 49 points (seven transect lines with seven equidistant points located 200 m apart) were overlain on each of the nine management units. We conducted point-count surveys during May from 0530 to 1030 hrs at all 441 points (49 points/site x 9 management units). We used a 100-m fixed radius for our samples to minimize the likelihood of double counting because this distance is the longest from which a Cerulean Warbler song can be heard (Hamel et al. 2009, Jones et al. 2000). We used playbacks to locate males singing on territory at each point (Falls 1981). We used a Sony Walkman Northeastern Naturalist Vol. 21, No. 4 J.R. Wagner and K. Islam 2014 517 attached to external speakers in 2010, and an mp3 player attached to external speakers in 2011 to broadcast recordings of male Cerulean Warbler songs. At each point, the observer listened for singing males for two minutes, played recorded Cerulean Warbler songs for one minute, and listened again for two minutes. The observer Figure 1. Nine management units located in Morgan-Monroe and Yellowwood state forests in Morgan, Monroe, and Brown counties in southern Indiana. Figure used with permission from Andrew Meier, Hardwood Ecosystem Experiment. Northeastern Naturalist 518 J.R. Wagner and K. Islam 2014 Vol. 21, No. 4 recorded the distance (m) and compass direction (azimuth degrees) of all detected males. To ensure the highest probability and accuracy of detecting singing Cerulean Warblers, we did not conduct surveys on rainy or windy days. We revisited all sites where males were detected, and relocated them using auditory and visual cues. If a male was not apparent on the revisit, we used the playback method described above to elicit a response. During these visits, two or more field observers followed male Cerulean Warblers and located perch trees visually or aurally. We defined a perch tree as a tree used by a male to perform a territorial song. We recorded GPS locations of males singing in perch trees until we had recorded at least five trees (range = 5–17) per male. Territory sizes determined by this method have not significantly changed from 2007 to present (Kaminski and Islam 2013). We marked perch trees with flagging to outline territorial boundaries. Most territories were demarcated on a single visit but ~10% of territories required a revisit to ensure that the minimum number of territory trees were included in the delineation. We used ArcGIS 10.0 (ESRI 2012) to demarcate territory boundaries as a minimum convex polygon. Reproductive monitoring We conducted preliminary nest surveys during 2010 and performed a more intense and thorough monitoring of breeding in 2011. Therefore, results from reproductive monitoring and breeding phenology (below) are reported only for 2011, but data for nest-site characteristics were derived from both years. We used behavioral cues to locate nests within a male’s territory. For example, females may “bungee” off a nest—fall quickly off-nest before beginning flight close to the ground—and males may “whisper sing” in the nest tree (K. Islam, pers. observ.; Rogers 2006). Once a nest was found, we monitored it between 0600 and 1700 hrs for at least 0.5 hrs (max of 1.5 hrs) every two days, or more frequently if we were anticipating fledging. We used a Nikon RAIII 82-mm spotting scope with an attached 20–60x eyepiece. Because nest height averaged 18 m above ground, we were not able to view nest contents directly, and we therefore based our assumptions of the nest stage on the parents’ behavior when nestlings could not be seen over the cup of the nest. A successful territory was defined as one from which at least one Cerulean Warbler fledged. For each observation, we recorded nesting stage (building, incubation, nestling, or fledgling), duration of female feeding bouts during incubation, number of parental feeding bouts for both sexes during the nestling stage, and the number of young. We averaged feeds-per-half-hour for each sex at each nest and used a paired t-test to compare male and female mean feeding rates at the same nest using Minitab 16.2.3 (Minitab 2011). We visited territories at least once post-delineation to survey for fledglings, even if a nest was not located. Although territory clustering occurred at many of our sites, in several instances a territory was sufficiently separated from another territory to allow us to attribute nest success to the territory being monitored. Because fledgling mobility can cause double counting, we conducted fledgling searches with multiple field observers for territories that were close together to ensure that a fledgling was Northeastern Naturalist Vol. 21, No. 4 J.R. Wagner and K. Islam 2014 519 not counted twice. At no point did we observe a fledgling outside an already demarcated territory, although we only found fledglings that were not yet capable of full flight. Because fledglings of many species produce loud begging calls, we located and identified all birds making begging calls within Cerulean Warbler territories. Vegetative characteristics of nest-sites We measured and recorded nest characteristics post-fledging: distance of nest from bole, nest height, distance of nest from the nearest foliage edge, and nest-tree height, species, and diameter at breast height (DBH). These variables have been collected across numerous other parts of the Cerulean Warbler range, allowing comparisons between our data with the findings of others to understand the plasticity of nest-site selection (e.g., Oliarnyk and Robertson 1996, Roth and Islam 2008). We measured the distance of the nest from the bole of the tree with a tape measure held between one observer standing below the nest and another at the trunk. We measured the distance to the closest canopy opening, defined as any break in foliage >20 m2, with a tape measure or rangefinder (Nikon Laser 440), and J. Wagner visually estimated the size of the canopy opening. We measured the nest height and nest-tree height with a rangefinder. We also noted the presence or absence of Parthenocissus quinquefolia L. (Virginia Creeper) around the nest and grapevines (Vitis spp.) within the territory. Descriptive statistics were generated using Minitab 16.2.3. Values are presented as means ± SE. We compared DBH, height, and frequency of species between nest trees and all available species in 2010 and 2011, based on vegetation data collected during surveys at the approximate center of territories (n = 51) and at randomly-generated points (n = 41). We created one 0.04-ha vegetation plot (James and Shugart 1970) at each location, consistent with previous studies (e.g., Bakermans and Rodewald 2009, Roth and Islam 2008). In each plot, we determined the canopy height using a rangefinder and measured the DBH of all trees >10 cm DBH. For comparisons of relative frequencies of trees within territories, we removed records of dead trees and species for which five or fewer total trees were found (7 species), except for species that had been used as nest trees. We determined relative species frequency by dividing the number of trees recorded for each species by the total number of trees. To determine relative frequencies of nest-tree species, we divided the number of times that species was used as a nest tree by the total number of nests located. Breeding phenology We defined peak incubation as the period during which the greatest number of nests were in the incubation stage. We calculated the time of peak incubation for nine nests based on observations of incubation and brooding at the nest. For nests found during the nestling stage (n = 5), we estimated the stage of nest activity based on fledging date. We also estimated fledge date for birds that we assumed were one-day post-fledged based on field observations of the presence of large amounts of down feathers, incomplete flight capability, and shape and color of bill (n = 5); no nest was located for these five territories. We assumed incubation and nestling periods were 11 and 10 days, respectively (Oliarnyk and Robertson 1996). Northeastern Naturalist 520 J.R. Wagner and K. Islam 2014 Vol. 21, No. 4 Table 1. Nest-site characteristics (mean ± SE) for Cerulean Warbler nests from 2010 and 2011 in Morgan-Monroe and Yellowwood state forests, IN (this study) and throughout other parts of the range. NS = not stated in manuscript. Distance Size Most frequently Distance of to closest of Nest used nest-tree Nest-tree Nest Nest-tree bole to canopy gap sample Study location species (% occurrence) DBH (cm) ht. (m) ht. (m) nest (m) opening (m) (m2) size Source Southeastern Ontario, CA Sugar Maple (67%) 40.2 ± 5.1 11.8 ± 0.6 17.7 ± 0.67 3.6 ± 0.3 33.4 ± 4.7A, NS 27 Oliarnyk and Robertson 1996 Cumberland Mountains, TN Sugar Maple (39%) 41.4 ± 1.4 18.3 ± 0.8 25.0 ± 1.7 3.5 ± 0.4 8.1 ± 0.7, ~10 38 Beachy 2008 Appalachian Mountains, TN Sugar Maple (% NS) 44.0 ± 0.7 19.8 ± 0.3 29.1 ± 0.5B 3.8 ± 0.1 2.2 ± 0.1, NS 479 Boves 2011 Southwestern MI Black Oak (50%) 45.5 ± 6.6 18.7 ± 2.1 21.8 ± 2.0 3.5 ± 0.6 17.7 ± 7.2, ≥25 6 Rogers 2006 Southwestern MI Black Locust (57%) 38.1 ± 2.9 19.0 ± 1.4 26.0 ± 1.1 3.8 ± 0.5 1.5 ± 0.8, ≥25 12 Rogers 2006 Southwestern MI NS 41.9 ± 1.0 20.1 ± 0.2 26.6 ± 4.0 4.1 ± 0.2 2.9 ± 0.3, ≥25 18 Rogers 2006 Southeast OH White Oak (60%) 44.2 ± 1.5 19.4 ± 0.5 NS 4.4 ± 0.2 NS 113 Bakermans 2008 Big Oaks NWR, Southeast IN Black WalnutC + 50.4 ± 25.8 18.4 ± 5.1D NS 4.8 ± 2.4 NS 43 Roth and Islam 2008 White Oak (53%) MMSF and YSF, Southeast IN White Oak (46%) 41.9 ± 3.1 18.4 ± 1.1 25.7 ± 1.2 4.4 ± 0.9 17.3 ± 3.7, ≥20 22E This study 95% conf. int.F 35.8, 48.0 16.2, 20.5 23.4, 28.0 2.6, 6.1 9.9, 24.6 AMeasured from nest tree, not nest. BCalculated by mean nest height + mean distance to top of crown. CJuglans nigra L. (Black Walnut). DIndicated as nest-tree height in results section, but referenced as nest height in discussion section. EDistance of bole to nest tree (n = 17), distance to closest canopy opening (n = 16). FBecause our nest-site characteristics are based on small sample sizes, 95% confidence intervals were often wide; thus. we caution that our comparisons of vegetation structure between this and other studies may not represent true differences. Northeastern Naturalist Vol. 21, No. 4 J.R. Wagner and K. Islam 2014 521 Results and Discussion Vegetative characteristics of nest sites We found differences between the vegetative characteristics of nest sites in our study and those of other recent projects (Table 1). Some notable differences were that absolute mean nest-tree DBH reported from Big Oaks National Wildlife Refuge (BONWR) in Indiana (Roth and Islam 2008) and the Appalachian Mountains in Tennessee (Boves 2011) were greater than in this study. At BONWR, Cerulean Warblers selected nest trees with a greater DBH than random or territory trees (Roth and Islam 2008), and in the Appalachian Mountains, average DBH was positively associated with nest-patch selection (Boves 2011). We found a similar trend in our study. Nest-tree DBH was 41.9 ± 3.1 cm, and random- and territorytree DBH averages were 27.1 ± 0.6 and 27.6 ± 0.7 cm, respectively. Thus, Cerulean Warblers appear to select relatively large trees for nest placement. Also, nest height and nest-tree height were greater in this study than in Ontario (Oliarnyk and Robertson 1996), although they were consistent with nest placement in other study areas (Table 1). Based on mean tree height in Cerulean Warbler territory (25.5 ± 0.3 m) and at random sites (24.5 ± 0.3 m), we conclude that Cerulean Warblers do not necessarily select the tallest trees for nest placement (mean nesttree height = 25.7 ±1.2), but perhaps choose larger trees based on basal area, as indicated by the tree-DBH selection. The distance to closest canopy gap values from our study were similar to findings from Michigan (Rogers 2006), yet in Ontario, distance to the closest gaps was greater (Oliarnyk and Robertson 1996). The most commonly used nesttree species was White Oak (Table 1). White Oak and, to a lesser degree, Sugar Maple were used as nest trees more than expected based on relative frequencies of trees documented during vegetation surveys (Fig. 2). A preference for White Oak was also found in Ohio (Bakermans 2008), and in the Appalachian Mountains (in addition to Sugar Maple and Magnolia acuminata L. [Cucumber-tree]; Boves 2011). Additionally, Cerulean Warblers have a preference for foraging in White Oaks (Gabbe et al. 2002, George 2009, MacNeil 2010). Cerulean Warbler preference for White Oak may be due to an association with high food availability in the canopy (Jeffries et al. 2006, Summerville et al. 2003) or the presence of grapevines in areas where White Oaks are found (Bakermans and Rodewald 2009). At our sites, oak and Carya spp. (hickory) trees were found to contain a greater abundance of Lepidoptera larva based on frass drop (Wagner 2012). Grapevines were present in most territories (83%), whereas grapevines were only found at 21.3% of non-use vegetation plots (J. Wagner, Ball State University, Muncie, IN, unpubl. data). Although not investigated in our study, grapevine density was positively associated with nest success in Ohio (Bakermans and Rodewald 2009), and grapevine bark is a common nest-building material (Beachy 2008, Boves and Buehler 2012). In fact, we collected one nest that fell after fledging and found it was composed almost entirely of grapevine bark. Thus, Cerulean Warblers may be attracted to habitat features that are correlated with the presence of White Oak. We found Northeastern Naturalist 522 J.R. Wagner and K. Islam 2014 Vol. 21, No. 4 Figure 2. Relative frequencies of tree species >10 cm DBH documented in vegetation plots in 51 Cerulean Warbler territories in 2011 (n = 530) and relative frequencies of nest-tree species located during 2010 and 2011 (n = 22). Abbreviations are as follows: ACRU (Acer rubrum), ACSA (Acer saccharum), CACO (Carya cordiformis), CAGL (Carya glabra), CALA (Carya laciniosa), CATO (Carya tomentosa), CAOV (Carya ovata), COFL (Cornus florida), FAGR (Fagus grandifolia), FRAM (Fraxinus americana), JUNI (Juglans nigra), LITU (Liriodendron tulipifera), NYSY (Nyssa sylvatica), PIST (Pinus strobus), QUAL (Quercus alba), QUPR (Quercus prinus), QURU (Quercus rubra), QUVE (Quercus velutina), and SAAL (Sassafras albidum). differences in Virginia Creeper cover, and thus concealment opportunities, at our project sites (1/17 nests) and those at BONWR, where over a third were concealed (Roth and Islam 2008). The differences may be due to local variation in habitat characteristics, a response to local predator levels, or the possibility that we did not find nests that were better-concealed at our sites (for 2011, we located 16 nests out of 101 territories). Concurrent studies on the tree communities at our study sites indicate that the conversion of oak–hickory-dominated stands to beech–maple-dominated stands may be occurring, as evidenced by the higher proportion of beech and maple saplings in the understory (Saunders and Arseneault 2013). This change may be detrimental to nesting success in areas where birds historically relied upon oaks for nesting. We recommend continued monitoring of the tree communities and Cerulean Warbler populations in other geographic areas so that optimal breedinghabitat requirements can be ascertained and further declines can be mitigated. Northeastern Naturalist Vol. 21, No. 4 J.R. Wagner and K. Islam 2014 523 Reproductive success In 2011, we documented an apparent nesting-success rate 30.7% across the 101 territories we demarcated (Table 2). This estimate is biased because we only monitored 12 nests, and in many cases we only visited a territory once during the fledgling period. We were unable to locate nests in the majority of territories, and we likely overlooked some successful nests. Additionally, we only analyzed nesting success in one year and, thus were not able to evaluate yearly differences. Nonetheless, we considered 24 territories to be successful based on fledglings alone; the number of fledglings was 2–3 (based on post-fledging surveys and monitored clutches). Studies in Michigan, the Mississippi Alluvial Valley, and BONWR, IN, reported relatively lower nesting success rates of 27%, 21%, and 16%, respectively (Buehler et al. 2008, Rogers 2006, and Roth and Islam 2008, respectively). It is worth noting that unlike our study, Buehler et al. (2008) reported only on outcomes from monitored nests and they did not include fledgling surveys. Higher overall nestsuccess rates were found in Ontario, Canada and in the Cumberland Mountains of Tennessee, where 40% and 46% of nests were successful, respectively (Buehler et al. 2008). Even higher rates of success were documented recently in the Cumberland Mountains, Tennessee (63%; Boves and Buehler 2012). Based on source/sink parameters (Pulliam 1988) and comparisons to population-growth rates across the breeding range (Buehler et al. 2008), Morgan-Monroe and Yellowwood state forests may be sinks for this species. We recommend further investigations at our sites to understand inter-annual variation in nesting success. In 2011, 5 of 12 nests failed: three failed during incubation for unknown reasons, one was partially torn from below, indicating that it probably failed due to predation, and one was no longer on its branch immediately following a hail-storm (Table 2). In 2010, we found a Molothrus ater (Boddert) (Brown-headed Cowbird) fledgling in association with a Cerulean Warbler. We observed the cowbird being fed first by a Vireo olivaceus L. (Red-eyed Vireo) adult and then a Cerulean Warbler male who chased off the Red-eyed Vireo. These causes of failure are similar to what was found in Tennessee, where abandonment was largely responsible for Table 2. Summary of Cerulean Warbler nest and territory monitoring in Morgan-Monroe and Yellowwood state forests, IN. Variable 2011 2010 # territories demarcated 101 N/A # territories sampled for vegetation 51 N/A # territories with nests located 16 6 # territories with active nests 12 5 # territories with fledglings (no nest located) 24 N/A # successful nests 7 N/A # failed nests, stage during failure 5, incubation N/A Cause of failure (n) Unknown (3) Cause of failure (n) Predation (1) Cause of failure (n) Weather (1) Northeastern Naturalist 524 J.R. Wagner and K. Islam 2014 Vol. 21, No. 4 failed nests; inferred predation, weather, and Brown-headed Cowbird parasitism were also responsible for some failed nests (Boves 201 1). Breeding phenology On 3 May 2011, we observed copulation in one pair and saw male “cup-forming” behavior (i.e., motioning to female about a suitable nest location by circling an area on a branch) in another pair. On 4 May 2011, we watched a female peeling bark off a grapevine, which is the main component in Cerulean Warbler nests. The first sighting of incubation was 10 May, and we estimate that nest was initiated between 3 and 9 May. In Tennessee and Texas, the earliest nest initiation was 26 April (Boves and Buehler 2012) and 17–26 April (Pulich 1988), respectively, whereas in Ontario, earliest initiation was much later—18 May (Oliarnyk and Robertson 1996). We were not on our sites until 3 May 2011, and earliest nest initiation could have been sooner, perhaps sometime in April. The first reported spring sighting of a Cerulean Warbler in Indiana was on 13 April 2011 in Eagle Slough Natural Area, Evansville, IN, which is approximately 200 km south of the project sites (Tim Griffith, IN-BIRD LISTSERV now accessed through the American Birding Association [birding.aba.org], pers. comm.). Seasonal conditions impact nesting phenology, however, and additional data would allow us to determine if our data represent typical timing. We found the first nest of the 2011 season on 8 May. The latest sighting of nestbuilding activity was 12 June, and incubation of that nest began on 15 June. The incubation peak was ~13–17 May (n = 9) or 22 May (n = 19) for nests observed directly and nests for which we estimated dates, respectively. The nestling peak was ~29–31 May (n = 7) or 30 May–7 June (n = 12) for observed nests and those for which we estimated dates, respectively. Comparisons with the only other breeding study in Indiana (BONWR) show similar phenology in incubating and nestling stages, with peak incubation occurring around 19 May in 2003 (K. Roth, Ball State University, Muncie, IN, unpubl. data); a second, smaller peak in incubating nests was also observed ~20 June. Birds may have been re-nesting after many nests failed early, probably due to weather conditions (Roth and Islam 2008). Our small sample sizes make it impossible to assess average incubation and nestling-stage lengths. However, it should be noted that two nests had 7–8-day nestling periods, shorter than had previously been recorded for this species. These nests were located approximately 50 m apart and close to a small foot trail. Chicks from both nests fledged on 31 May 2011, and it is possible that a disturbance caused premature fledging. It is also possible that we missed hatching dates because our nest observations were only a minimum of 30 min, and it was not possible to view inside the nest; however, female behavior (such as poking her head into the nest or rearranging herself often) or male behavior (such as moving closer to the nest, guarding from a nearby branch, or vocally coordinating watch effort with the female) did not indicate that hatching had yet taken place during those observations. Incubation periods for these two nests were 12 and 1 1 days, respectively. Northeastern Naturalist Vol. 21, No. 4 J.R. Wagner and K. Islam 2014 525 Feeding rates During incubation, females spent 6.4 ± 0.9 min (range = 2–15 min, n =14) per half hour foraging off the nest, and single feeding bouts averaged 4.7 ± 0.5 min (range = 2–9 min, n = 14 observations). These foraging times indicated that females spent ~23 min incubating per half hour, a period consistent with studies from Ontario, Canada, which reported that females incubated 50.0 ± 5.3 min per hour (Oliarnyk and Robertson 1996) and 25.7 ± 0.3 min per half hour (Barg et al. 2006). During the nestling stage of these same five nests plus another nest found during this stage, adults returned to the nest to feed their young 3.4 ± 1.6 times per 30-min site visit. These provisioning rates are similar to those found in Tennessee (Boves 2011), but are higher than provisioning rates in Ontario (Barg et al. 2006, Oliarnyk and Robertson 1996). These differences may reflect regional variations in prey phenology or more food-rich environments in southern parts of the range. We noted the sex of the feeding parent in 58 feeds during 18 half-hour visits at five nests. Mean feeding rates of males (2.2 ± 0.2 feeds/half hour) and females (1.4 ± 0.5 feeds/half hour) were not significantly different (t [4] = 1.48, P = 0.21); our small sample size of only five nests suggests that statistical comparisons may not have much utility. However, our results are supported by the findings from other studies in Tennessee (Boves 2011) and Ontario (Barg et al. 2006) with larger sample sizes (56 and 31 nests, respectively), which reported similar provisioning rates for males and females. Although not investigated in this study, differences in provisioning rates between the sexes may exist at different times during the nestling stage. At BONWR, in Indiana, females fed six-day-old nestlings more often than males (Allen and Islam 2004). Barg et al. (2006) found that females fed older nestlings more often than younger nestlings, but successful nests had higher rates of male provisioning. Further investigations into variations in prey used across the range may help us understand how differences in provisioning rates and adult behavior are environmentally influenced. Additional research is needed to identify the effects of feeding rate and prey quality on nesting success. Some prey species have higher nutritional value than others, and habitat characteristics influence the spatial and temporal distribution of quality prey items because insect presence is largely determined by vegetation. Understanding the role of habitat characteristics in providing energy-rich prey items for foraging adults and growing nestlings will aid in the identification of quality habitat. Acknowledgments This paper is a contribution of the Hardwood Ecosystem Experiment, a partnership of the Indiana Department of Natural Resources, Indianapolis, IN; Purdue University, West Lafayette, IN; Ball State University, Muncie, IN; Indiana State University, Terre Haute, IN; Drake University, Des Moines, IA; Indiana University of Pennsylvania, Indiana, PA; and the Indiana Chapter of The Nature Conservancy. Funding for this project was provided by the Indiana Department of Natural Resources through Purdue University, the Amos W. Butler Audubon Society, and Ball State University’s ASPiRE program. We would like Northeastern Naturalist 526 J.R. Wagner and K. Islam 2014 Vol. 21, No. 4 to thank S. Auer, two anonymous reviewers, and R. Renfrew for many helpful comments on drafts of this manuscript. Special thanks to R. Dibala for finding many nests included in this study. Additionally, we appreciate the hard work of R. Dibala, P. Bradley, E. Koscielniak, D. Rupp, J. Schindler, and A. Wilson for assistance with field research, and E. Arnold for assistance with data entry. We thank G. Dodson and D. LeBlanc for suggestions on the research and R. Kalb and J. Riegel for help with field logistics. Literature Cited Allen, J., and K. Islam. 2004. Gender differences in parental feeding effort of Cerulean Warbler at Big Oaks National Wildlife Refuge, Indiana. Proceedings of the Indiana Academy of Science 113:162–165. Bakermans, M.H. 2008. Demography and habitat use of Cerulean Warblers on breeding and wintering grounds. Ph.D. Dissertation. Ohio State University, Columbus, OH. 175 pp. 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 Management 258:224–232. 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. The Wilson Journal of Ornithology 118:316–325. 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