Declines of Aerial Insectivores in North America Follow a Geographic Gradient

Nebel, Silke; Mills, A. K.; McCracken, Jon D.; Taylor, Philip D.

doi:10.5751/ace-00391-050201

Cited by 223 publications

(274 citation statements)

References 47 publications

(41 reference statements)

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“…Here, we examine nest box occupancy rates of Tree Swallows to evaluate whether these data suggest spatiotemporal patterns of population changes. We also evaluate whether these data produce conclusions similar to those of Nebel et al (2011). Similar results from both sources of data would add credence to patterns reported by Nebel et al (2011).…”

Section: Introductionsupporting

confidence: 56%

“…Previous studies have suggested that populations of North American aerial avian insectivores are decreasing (Robbins et al 1989, Böhning-Gaese et al 1993, Askins 1995 Nebel et al (2011) concluded that Tree Swallow (Tachycineta bicolor) populations were among the species of decreasing aerial insectivores, especially in northeastern North America. BBS data, such as those analyzed by Nebel et al (2011), are collected along roads, and are most concentrated near areas of high human population density (see Sauer et al 2011 for details on spatiotemporal coverage).…”

Section: Introductionmentioning

confidence: 99%

“…BBS data, such as those analyzed by Nebel et al (2011), are collected along roads, and are most concentrated near areas of high human population density (see Sauer et al 2011 for details on spatiotemporal coverage). In many parts of their range, distribution of Tree Swallows is patchy, and if BBS routes do not adequately sample these patches, swallow population trends may not be clearly discerned.…”

Section: Introductionmentioning

confidence: 99%

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Spatiotemporal Patterns in Nest Box Occupancy by Tree Swallows Across North America

Shutler¹,

Hussell²,

Norris³

et al. 2012

ACE

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ABSTRACT. Data from the North American Breeding Bird Survey (BBS) suggest that populations of aerial insectivorous birds are declining, particularly in northeastern regions of the continent, and particularly since the mid-1980s. Species that use nest boxes, such as Tree Swallows (Tachycineta bicolor), may provide researchers with large data sets that better reveal finer-scale geographical patterns in population trends. We analyzed trends in occupancy rates for ca. 40,000 Tree Swallow nest-box-years from 16 sites across North America. The earliest site has been studied intensively since 1969 and the latest site since 2004. Nest box occupancy rates declined significantly at five of six (83%) sites east of -78° W longitude, whereas occupancy rates increased significantly at four of ten sites (40%) west of -78° W longitude. Decreasing box occupancy trends from the northeast were broadly consistent with aspects of a previous analysis of BBS data for Tree Swallows, but our finding of instances of increases in other parts of the continent are novel. Several questions remain, particularly with respect to causes of these broadscale geographic changes in population densities of Tree Swallows. The broad geographic patterns are consistent with a hypothesis of widespread changes in climate on wintering, migratory, or breeding areas that in turn may differentially affect populations of aerial insects, but other explanations are possible. It is also unclear whether these changes in occupancy rates reflect an increase or decrease in overall populations of Tree Swallows. Regardless, important conservation steps will be to unravel causes of changing populations of aerial insectivores in North America.RÉSUMÉ. Les données provenant du Relevé des oiseaux nicheurs (BBS) de l'Amérique du Nord semblent indiquer que les populations d'insectivores aériens sont en déclin, particulièrement dans les régions du nord-est du continent et depuis le milieu des années 1980. Grâce aux espèces qui utilisent les nichoirs, comme l'Hirondelle bicolore (Tachycineta bicolor), les chercheurs ont accès à une grande quantité de données qui révèlent davantage les tendances des populations à l'échelle fine. Nous avons analysé la tendance du taux d'occupation par l'Hirondelle bicolore à partir de 40 000 nichoirs-années provenant de 16 sites répartis en Amérique du Nord. Le site le plus ancien est suivi intensivement depuis 1969 et le plus récent, depuis 2004. Le taux d'occupation des nichoirs a diminué significativement dans 5 des 6 sites (83 %) situés à l'est du 78° de longitude ouest, tandis qu'il a augmenté significativement dans 4 des 10 sites (40 %) à l'ouest du 78° de longitude ouest. La tendance à la baisse de l'occupation observée dans le nord-est concorde dans les grandes lignes avec les résultats d'une analyse antérieure des données du BBS pour cette espèce, mais les hausses que nous avons observées dans d'autres régions de l'Amérique du Nord s'avèrent nouvelles. Plusieurs interrogations demeurent, notamment en ce qui a trait aux causes de ces chang...

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Section: Introductionsupporting

confidence: 56%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Spatiotemporal Patterns in Nest Box Occupancy by Tree Swallows Across North America

Shutler¹,

Hussell²,

Norris³

et al. 2012

ACE

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“…Most negative trends have occurred in Canada and the northern USA since the late 1960s, while more southern breeding populations have remained stable or have slightly increased (Sauer et al 2012), and these trends appear to be characteristic of most aerial insectivores breeding in North America (Nebel et al 2010, NABCI Canada 2012. This situation provides a useful comparative paradigm whereby the strength of migratory connectivity can be investigated across regions with different population trends.…”

Section: Introductionmentioning

confidence: 99%

“…North American breeding populations of Barn Swallow have decreased drastically in recent decades but causes of declines remain largely unknown (Cadman et al 2007, McGowan and Corwin 2008, Nebel et al 2010, Bird Studies Canada et al 2012. Most negative trends have occurred in Canada and the northern USA since the late 1960s, while more southern breeding populations have remained stable or have slightly increased (Sauer et al 2012), and these trends appear to be characteristic of most aerial insectivores breeding in North America (Nebel et al 2010, NABCI Canada 2012.…”

Section: Introductionmentioning

confidence: 99%

A multi‐isotope (δ²H, δ¹³C, δ¹⁵N) approach to establishing migratory connectivity of Barn Swallow (Hirundo rustica)

García-Pérez

Hobson

2014

Ecosphere

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Establishing geographic links between different stages of the annual cycle of migratory species is fundamental to evaluating factors limiting their populations. Stable isotope measurements (δ13C, δ15N, and δ2H) of feathers combined with a knowledge of how these isotopes are structured spatially in foodwebs can be used to establish molt origins and migratory connectivity. Here, we investigated patterns of migratory connectivity between North American breeding grounds and South American wintering grounds of stable (n = 3) and declining (n = 9) populations of Barn Swallow (Hirundo rustica) in North America using a probabilistic assignment to multi‐isotope feather clusters derived for 488 winter‐grown feathers collected during the breeding season (2009 to 2012). Our study did not find evidence for differential degree of migratory connectivity between increasing/stable and declining populations of Barn Swallows but found a longitudinal structure in breeding and wintering ground origins of populations. Probable wintering areas for northern and western breeding birds corresponded with western regions of South America, while birds breeding in southern and eastern North America tended to occupy areas in north‐eastern South America. Possible factors contributing to the differential population trends between stable or increasing and declining breeding populations could be related to habitat quality of the different wintering areas, changes in climate, and the cost of long‐distance migration. The use of a multi‐isotope approach and the combination of prior information on geographic distribution of vegetation types, based on δ13C measurements, effectively constrained geographic origins of swallows and our approach can be applied to defining migratory connectivity for other species.

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Conservation implications of a lack of relationship between baseline glucocorticoids and fitness in a wild passerine

Madliger

Love

2016

Ecological Applications

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The application of physiological measures to conservation monitoring has been gaining momentum and, while a suite of physiological traits are available to ascertain disturbance and condition in wildlife populations, glucocorticoids (i.e., GCs; cortisol and corticosterone) are the most heavily employed. The interpretation of GC levels as sensitive indicators of population change necessitates that GCs and metrics of population persistence are linked. However, the relationship between GCs and fitness may be highly context-dependent, changing direction, or significance, depending on the GC measure, fitness metric, life history stage, or other intrinsic and extrinsic contexts considered. We examined the relationship between baseline plasma corticosterone (CORT) levels measured at two periods of the breeding season and three metrics of fitness (offspring quality, reproductive output, and adult survival) in female Tree Swallows (Tachycineta bicolor). Specifically, we investigated whether (1) a relationship between baseline CORT metrics and fitness exists in our population, (2) whether the inclusion of energetic contexts, such as food availability, reproductive investment, or body mass, could alter or improve the strength of the relationship between CORT and fitness, and (3) whether energetic contexts could better predict fitness compared to CORT metrics. Importantly, we investigated these relationships in both natural conditions and under an experimental manipulation of foraging profitability (feather clipping) to determine the influence of an environmental constraint on GC-fitness relationships. We found a lack of relationship between baseline CORT and both short- and long-term metrics of fitness in control and clipped birds. In contrast, loss in body mass over reproduction positively predicted reproductive output (number of chicks leaving the nest) in control birds; however, the relationship was characterized by a low R (5%), limiting the predictive capacity, and therefore the application potential, of such a measure in a conservation setting. Our results stress the importance of ground-truthing GC-fitness relationships and indicate that baseline GCs will likely not be easily employed as conservation biomarkers across some species and life history stages. Given the accumulating evidence of temporally dynamic, inconsistent, and context-dependent GC-fitness relationships, placing effort towards directly measuring fitness traits, rather than plasma GC levels, will likely be more worthwhile for many conservation endeavours.

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Declines of Aerial Insectivores in North America Follow a Geographic Gradient

Cited by 223 publications

References 47 publications

Spatiotemporal Patterns in Nest Box Occupancy by Tree Swallows Across North America

Spatiotemporal Patterns in Nest Box Occupancy by Tree Swallows Across North America

A multi‐isotope (δ²H, δ¹³C, δ¹⁵N) approach to establishing migratory connectivity of Barn Swallow (Hirundo rustica)

Conservation implications of a lack of relationship between baseline glucocorticoids and fitness in a wild passerine

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Declines of Aerial Insectivores in North America Follow a Geographic Gradient

Cited by 223 publications

References 47 publications

Spatiotemporal Patterns in Nest Box Occupancy by Tree Swallows Across North America

Spatiotemporal Patterns in Nest Box Occupancy by Tree Swallows Across North America

A multi‐isotope (δ2H, δ13C, δ15N) approach to establishing migratory connectivity of Barn Swallow (Hirundo rustica)

Conservation implications of a lack of relationship between baseline glucocorticoids and fitness in a wild passerine

Contact Info

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A multi‐isotope (δ²H, δ¹³C, δ¹⁵N) approach to establishing migratory connectivity of Barn Swallow (Hirundo rustica)