Marja H. Bakermans

SCALE-DEPENDENT HABITAT USE OF ACADIAN FLYCATCHER (EMPIDONAX VIRESCENS) IN CENTRAL OHIO

Abstract We used a multiscale approach to examine use of riparian forests by Acadian Flycatchers (Empidonax virescens) at three distinct scales: microsite (nest or territory), local stand (3-ha patch of forest), and landscape (1-km-radius area). We examined the extent to which understory arthropod biomass, vegetation structure, and breeding productivity affected habitat use by Acadian Flycatchers across 36 mature riparian forests along an urbanization gradient in central Ohio, 2001–2002. Using an information-theoretic approach, we found that although vegetation structure and understory arthropod biomass were associated with nest and territory location at small spatial scales, they failed to explain habitat use across stands. Instead, percentage of urban cover in the landscape best explained variation in the abundance of Acadian Flycatchers among stands. In fact, Acadian Flycatchers were >3× more abundant in the most rural (≤1% urban) riparian forests than in the more urban (≥10% urban) riparian forests. Nest survival and productivity also declined as urban development increased within the landscape. We suggest that increased nest predation in urban riparian forests, coupled with either reduced productivity or site fidelity or both, may be an underlying mechanism of landscape-scale patterns. Results suggest that explicit consideration of multiple spatial scales, and especially landscape matrix composition, is critical for understanding habitat use. Uso del Hábitat Dependiente de la Escala por parte de Empidonax virescens en el Centro de Ohio

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.

American Woodcock and Golden-Winged Warbler Abundance and Associated Vegetation in Managed Habitats

Abstract Vermivora chrysoptera (Golden-winged Warbler) and Scolopax minor (American Woodcock, hereafter, Woodcock) are 2 young-forest-dependent species of eastern North America that are experiencing population declines due to loss of breeding habitat. The goals of our study were to compare avian abundance and habitat similarities and differences in sites used by the 2 species. A portion of our survey plots were manipulated under Woodcock or Golden-winged Warbler habitat prescriptions in managed shrublands, and others were on regenerating timber-harvest sites. In north-central PA, we compared Woodcock abundance in 10-ha experimental plots assigned to one of 3 habitat prescriptions: uncut controls, Woodcock strip plots, and Golden-winged Warbler mosaic plots. We also quantified vegetation characteristics in each 10-ha study plot. Woodcock density was higher in the strip (4.8 males/10 ha) and mosaic (5.1 males/10 ha) plots compared to the uncut reference plots (3.3 males/10 ha). Woodcock density was negatively correlated with sapling cover in the north-central PA study plots. In regenerating timber harvests in northeastern PA, we demonstrated that vegetation characteristics overlap regardless of whether we detected only Woodcock or both species. Mean basal area of harvested stands with only Woodcock (i.e., 11.5 m2/ha) was greater than the mean basal area in stands used by Golden-winged Warbler (8.4 m2/ha). Our results suggest that creation of young forests at the stand level using either the Woodcock or Golden-winged Warbler habitat guidelines has benefits for both species. However, the Golden-winged Warbler is less flexible in the density of herbaceous cover and residual trees it requires. We recommend that in areas where the 2 species coexist, the Golden-winged Warbler guidelines be implemented to benefit both species.

A case of mistaken identity: understanding the stimulus of agonism between two wood warblers

When multiple species occur sympatrically, divergence in morphological and behavioural traits associated with species recognition and resource use are expected. Individuals that engage in interspecific aggression often suffer fitness consequences if the benefits of securing resources do not outweigh the risks associated with agonism. In the southern Appalachians, interspecific aggression frequently occurs between chestnut-sided warblers, Setophaga pensylvanica, and golden-winged warblers, Vermivora chrysoptera, a species that is experiencing sharp declines in population numbers. Using a combination of correlative and experimental approaches, we explored two potential explanations for interspecific aggression: interspecific competition and mistaken identity. It is commonly inferred that aggressive interactions are the product of competition due to an ecological niche overlap. However, because these warblers have similar crown coloration and aggressive interactions appear stochastic, aggression may be a result of mistaken identity. First, in 2014, we documented spatial overlap of the two species and measured reproductive success and habitat preference (using remote sensing) of golden-winged warblers. We found that golden-winged warblers that settled among high densities of chestnut-sided warblers were more aggressive, but chestnut-sided warbler density did not negatively influence their reproductive success; rather, habitat structure best predicted reproductive success. Next, in 2015, we tested for misidentification using models of conspecifics and heterospecifics in simulated territorial intrusions. We found that both warbler species were equally likely to both types of models, and that the most aggressive individuals were more likely to attack models. Our results suggest that, from the golden-winged warblers perspective, sympatry is not detrimental and aggression is probably a function of mistaken identity. Yet, these behavioural interactions should be maladaptive, which may lead to the segregation of habitat types or divergence in crown morphology between species.

Geography and age are related to plumage coloration of male Golden-winged Warblers (Vermivora chrysoptera)

ABSTRACT Although plumage displays often reliably signal individual condition and age, how these sexually selected traits vary with geographic region is not well understood. Golden-winged Warbler (Vermivora chrysoptera) populations are fragmented and declining precipitously in the Appalachian Mountains. Limited research suggests that Golden-winged Warbler facial plumage ornaments may be under sexual selection; black throat (melanin-based) coloration is associated with mate acquisition while yellow crown (carotenoid-based) coloration is associated with aggression and habitat quality. We tested whether multiple plumage traits (crown, throat, and tail coloration) (1) varied across the Appalachian breeding range, (2) varied with age class or body condition, and (3) covaried with each other and whether the covariance differed with geographic region. We found that crown and throat coloration followed a latitudinal gradient, with the more southern birds showing lower ornamentation. Moreover, after-second-year birds had tails with a greater extent of white than second-year, suggesting tail color may reliably signal age that conspecifics could assess. Males with more-ornamented crown color had more-ornamented throat coloration, suggesting that this species demonstrates some potential for both redundant (facial coloration) and independent (tail white) signaling. We found no evidence, however, that covariation between traits differed across the breeding range or that the plumage traits varied with body condition. Additional research investigating the signaling function of multiple plumage ornaments in Golden-winged Warblers across their breeding range could shed light on habitat preferences and communication. Received 28 October 2016. Accepted 4 January 2018.

First Record of the White-tipped Sicklebill (Eutoxeres aquila aquila: Trochilidae) for Venezuela

Abstract A female White-tipped Sicklebill (Eutoxeres aquila aquila) was caught on 3 February 2006 at 1,050 m elevation in Agua Blanca, Municipio Andrés Bello, Mérida, Venezuela, 2 km southeast of La Azulita. This account represents the first record of this hummingbird species in Venezuela, extending the taxons known distribution at least 500 km northeastward.