Felicity L. Newell

Emulating Natural Disturbances for Declining Late-Successional Species: A Case Study of the Consequences for Cerulean Warblers (Setophaga cerulea)

Forest cover in the eastern United States has increased over the past century and while some late-successional species have benefited from this process as expected, others have experienced population declines. These declines may be in part related to contemporary reductions in small-scale forest interior disturbances such as fire, windthrow, and treefalls. To mitigate the negative impacts of disturbance alteration and suppression on some late-successional species, strategies that emulate natural disturbance regimes are often advocated, but large-scale evaluations of these practices are rare. Here, we assessed the consequences of experimental disturbance (using partial timber harvest) on a severely declining late-successional species, the cerulean warbler (Setophaga cerulea), across the core of its breeding range in the Appalachian Mountains. We measured numerical (density), physiological (body condition), and demographic (age structure and reproduction) responses to three levels of disturbance and explored the potential impacts of disturbance on source-sink dynamics. Breeding densities of warblers increased one to four years after all canopy disturbances (vs. controls) and males occupying territories on treatment plots were in better condition than those on control plots. However, these beneficial effects of disturbance did not correspond to improvements in reproduction; nest success was lower on all treatment plots than on control plots in the southern region and marginally lower on light disturbance plots in the northern region. Our data suggest that only habitats in the southern region acted as sources, and interior disturbances in this region have the potential to create ecological traps at a local scale, but sources when viewed at broader scales. Thus, cerulean warblers would likely benefit from management that strikes a landscape-level balance between emulating natural disturbances in order to attract individuals into areas where current structure is inappropriate, and limiting anthropogenic disturbance in forests that already possess appropriate structural attributes in order to maintain maximum productivity.

Spatial variation in breeding habitat selection by Cerulean Warblers (Setophaga cerulea) throughout the appalachian mountains

ABSTRACT. Studies of habitat selection are often of limited utility because they focus on small geographic areas, fail to examine behavior at multiple scales, or lack an assessment of the fitness consequences of habitat decisions. These limitations can hamper the identification of successful site-specific management strategies, which are urgently needed for severely declining species like Cerulean Warblers (Setophaga cerulea). We assessed how breeding habitat decisions made by Cerulean Warblers at multiple scales, and the subsequent effects of these decisions on nest survival, varied across the Appalachian Mountains. Selection for structural habitat features varied substantially among areas, particularly at the territory scale. Males within the least-forested landscapes selected microhabitat features that reflected more closed-canopy forest conditions, whereas males in highly forested landscapes favored features associated with canopy disturbance. Selection of nest-patch and nest-site attributes by females was more consistent across areas, with females selecting for increased tree size and understory cover and decreased basal area and midstory cover. Floristic preferences were similar across study areas: White Oak (Quercus alba), Cucumber-tree (Magnolia acuminata), and Sugar Maple (Acer saccharum) were preferred as nest trees, whereas red oak species (subgenus Erythrobalanus) and Red Maple (A. rubrum) were avoided. The habitat features that were related to nest survival also varied among study areas, and preferred features were negatively associated with nest survival at one area. Thus, our results indicate that large-scale spatial heterogeneity may influence local habitat-selection behavior and that it may be necessary to articulate site-specific management strategies for Cerulean Warblers.

WOOD THRUSH NESTS IN DENSE UNDERSTORY MAY BE VULNERABLE TO PREDATORS

Abstract We used Mayfield logistic regression and an information-theoretic approach to examine habitat characteristics associated with nesting success of Wood Thrushes (Hylocichla mustelina) across an urban to forested gradient in southwestern Pennsylvania in 2003 and 2004. Both nest placement and number of understory stems provided equally plausible models. Mayfield success was 20% higher for nests >3 m above ground level while dense understory was associated with low nest height. Wood Thrush nests in the forest interior averaged 2 m higher with a third less understory than edge nests. Urbanization and distance to the forest edge were not useful predictors of Wood Thrush nest success. The analysis was confounded by low breeding density at the most urbanized sites, but we found moderate success (42%, n = 63) across a fragmented landscape with minimal core forest area. Interior nests in a large contiguous forest were twice as successful (60%, n = 31) compared to edge nests (25%, n = 33) adjacent to a small housing development. We do not know the mechanism underlying increased predation of low understory nest sites that we observed. The ability of Wood Thrushes to see and/or effectively attack a predator in the area may be important for nest defense; changes in the predator community associated with forest edges may also explain differences in nest success. The relationship between nest placement, nest defense, and the predator community needs further study.

Occurrence of Polygyny and Double Brooding In the Eastern Wood-Pewee

Abstract We document the first confirmed cases of polygyny and double brooding in the Eastern Wood-Pewee (Contopus virens). During an intensive study of the effects of shelterwood harvesting on canopy-nesting songbirds in southeastern Ohio, 2007–2010, we color-banded 79 Eastern Wood-Pewees and monitored 237 pewee nests. In 2007, we confirmed a color-banded male provisioning at two concurrently active nests; the male was polygynous in at least two consecutive years. In 2009, we observed an unbanded female feeding fledglings and subsequently shaping a nest from which young had recently fledged; the female successfully fledged two broods from the same nest. In addition to confirmed observations, we identified several other probable cases of polygyny and double brooding. In our upland oak system, we estimated rates of polygyny from 6–22% with the greatest occurrence of polygyny during a dry spring in 2007; rates of double brooding may have been as high as 6–12%. Males appeared to benefit from polygyny, because males paired with two females fledged twice as many young compared to monogamous males, without any apparent negative effect on return rate. Overall, we did not find negative effects on reproductive success for females paired with polygynous males, although we were not able to consistently differentiate between primary and secondary females. Polygyny appeared to be related to either territory quality and/or male quality with nests of polygynous males located in preferred nest sites while provisioning rates were greater at polygynous compared to monogamous nests. In addition, we only found experienced males paired with two females. Both males and females benefited from double brooding, fledging twice as many young as single brooded pairs, but in our system double brooding appeared to be limited by high levels of nest predation early in the breeding season.

JUVENAL PLUMAGE IN THE GREEN-BREASTED MOUNTAIN-GEM (LAMPORNIS SYBILLAE) WITH OBSERVATIONS ON TIMING OF BREEDING AND MOLT

Abstract We documented the juvenal plumage of the Green-breasted Mountain-gem (Lampornis sybillae) during mist-netting operations in the cloud forest at La Tigra National Park, Honduras from February to April 2006. A recently-fledged juvenile of this species was caught on 17 March and, contrary to previous suggestions, we found the throat and breast were mottled green. Ninety-eight immature mountain-gems intermediate between this juvenal plumage and that of adults were also caught during our study. Both males and females of the Green-breasted Mountain-gem apparently begin replacing juvenal throat feathers soon after fledging and prior to molting flight feathers. A high capture rate of young hummingbirds at the end of the dry season, including recent fledglings and individuals showing only traces of juvenal plumage, suggests a protracted breeding season that we estimate to last at least from November through March. We also caught adults in a variety of stages of flight-feather molt, perhaps part of a transition from breeding; molting in our population is estimated to span at least an 8-month period.