Aerial insectivores (birds that forage on aerial insects) have experienced significant population declines in North America. Numerous hypotheses have been proposed for these declines, but current evidence suggests multiple factors could be operating in combination during their annual migratory cycles between breeding and nonbreeding areas. Potential drivers include decreased prey abundance, direct or indirect impacts of environmental contaminants, habitat loss, phenological changes due to warming climate, and conditions on migratory stopover or wintering grounds. While no single threat appears to be the cause of aerial insectivore declines, existing evidence suggests that several of these factors could be contributing to the declines at different times in the annual lifecycle. Breeding productivity for most of these species does not appear to be limited by overall prey abundance, contaminants, or habitat loss, which suggests that similar issues on nonbreeding grounds or carryover effects could play important roles. However, a better understanding of the importance of prey quality throughout the lifecycle is critically needed. Based on current evidence, we propose that changes in availability of high-quality prey, with variability across breeding and nonbreeding grounds, reduce various combinations of fledging success, post-fledging survival, and nonbreeding season body condition of aerial insectivores, resulting in species and geographic differences in population trends. We encourage others to use this hypothesis as a starting point to test specific mechanisms by which availability of high-quality prey influences demographic parameters. We suggest that future research focus on defining prey quality, monitoring insect abundance in conjunction with birds, comparing demographic models across local populations experiencing different population growth rates, and using tracking technology to document important migratory and nonbreeding areas. Considerable research progress already has been made, but additional research is needed to better understand the complex web of potential causes driving aerial insectivore declines.

Populations of the eastern whip‐poor‐will (Antrostomus vociferus; whip‐poor‐will) have declined throughout most of its range, making it a species of high conservation concern in nearly every state and province where it occurs. Researchers have reported whip‐poor‐wills are associated with forest stands with open canopies, and thus silviculture may be a promising means for promoting their populations, yet the ecological literature does not quantify fine‐scale habitat relationships capable of assisting with silviculture prescriptions. Our objective was to quantify the associations between whip‐poor‐wills, canopy openness, and other vegetation characteristics to provide managers with guidance for whip‐poor‐will management. Based on prior research, we hypothesized that whip‐poor‐wills may be associated with intermediate levels of canopy retention and that their numbers would also be affected by understory characteristics. We surveyed whip‐poor‐wills with point counts in managed forest at the Fort Drum Army installation in New York, USA, during 2015 and 2016 and collected vegetation measurements at each point count location to relate whip‐poor‐will occupancy with vegetation structure and composition. Whip‐poor‐will occupancy was strongly related to intermediate levels of basal area, with peak occupancy at 13.8 m2/ha, a value that corresponds to forest denser than most shrublands but more open than closed‐canopy forest. Whip‐poor‐will presence was negatively related to understory height, which is consistent with prior studies. These findings provide managers with quantitative targets that can be used to increase or maintain whip‐poor‐will numbers and abundance of other disturbance‐associated species similarly unable to persist in unmanaged forests stands. © 2021 The Wildlife Society.

The Eastern Whip-poor-will (Antrostomus vociferus: hereafter whip-poor-will) has been declining from historical population levels throughout its range in the northeast. Although whip-poor-wills have been reported to use a variety of habitats, most recent studies have associated whip-poor-wills with open canopy habitats, such as early-successional habitats or forest edges. However, there remain substantial gaps in our understanding of whip-poor-wills' habitat associations. For example, historical accounts state that whip-poor-wills roost and nest in forest and forage in openings, and thus, managers advocate the juxtaposition of habitats based on this supposition. Nevertheless, a quantitative evaluation of the habitat used for these activities is lacking. For this reason, we radiotracked 10 adult whip-poor-wills using radio telemetry in upstate New York and collected vegetation measurements at a subset at these points where the birds were either foraging at night or roosting during the day, as well as at any identified nest sites. Comparisons of the vegetation measurements revealed that foraging habitat was significantly more open than roosting habitat, as foraging habitat had lower tree density, basal area, and understory height. Contrary to historical accounts, the few nest sites found in this study were located in areas that had low basal area, similar to the habitat at foraging locations. These results suggest that although creating more opencanopy habitat may benefit whip-poor-wills by providing suitable foraging habitat, and potentially nesting habitat, maintaining denser forest within proximity to these open areas may also provide valuable cover for roosting whip-poor-wills.RESUMEN. El pato silbador oriental (Antrostomus vociferus) ha disminuido su población comparada con niveles históricos en toda su área de distribución en el noreste. Aunque se ha informado que A. vociferus utilizan diversos hábitats, la mayoría de los estudios recientes han asociado a A. vociferus con hábitats de dosel abierto, como los hábitats de transición temprana o los bordes de los bosques. Sin embargo, siguen existiendo importantes vacíos en nuestro conocimiento de las asociaciones de hábitat por parte de especies de este género. Por ejemplo, los relatos históricos afirman que A. vociferus se perchaba y anidaba en el bosque y se alimentaba en los claros, por lo que los gestores abogan por la yuxtaposición de hábitats basándose en esta suposición. Sin embargo, se carece de una evaluación cuantitativa del uso hábitat para estas actividades. Por este motivo, hemos puesto radios en 10 adultos de A. vociferus para utilizar radiotelemetría en el norte del estado de Nueva York y hemos colectado mediciones de la vegetación en un subconjunto de estos puntos en los que los pájaros buscaban comida por la noche o se perchaban durante el día, así como en los lugares de nidificación identificados. Las comparaciones de las mediciones de la vegetación revelaron que el hábitat de búsqueda de alimento era significativamente más abierto que el hábita...

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