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Anthropogenic noise is a ubiquitous feature of the American landscape, and is a known stressor for many bird species, leading to negative effects in behavior, physiology, reproduction, and ultimately fitness. While a number of studies have examined how anthropogenic noise affects avian fitness, there are few that simultaneously examine how anthropogenic noise impacts the relationship between parental care behavior and nestling fitness. We conducted Brownian noise playbacks for 6 h a day during the nesting cycle on Eastern Bluebird (Sialia sialis) nest boxes to investigate if experimentally elevated noise affected parental care behavior, nestling body conditions, and nestling stress indices. We documented nest attendance by adult females using radio frequency identification (RFID), and we assessed nestling stress by measuring baseline corticosterone levels and telomere lengths. Based on the RFID data collected during individual brood cycles, adult bluebirds exposed to noise had significantly higher feeding rates earlier in the brood cycle than adults in the control group, but reduced feeding rates later in the cycle. Nestlings exposed to noise had higher body conditions than the control nestlings at 11 days of age, but conditions equalized between treatments by day 14. We found no differences in nestling baseline corticosterone levels or nestling telomere lengths between the two treatment groups. Our results revealed that noise altered adult behavior, which corresponded with altered nestling body condition. However, the absence of indicators of longer-term effects of noise on offspring suggests adult behavior may have been a short-term response.

Recent studies suggest that visual and acoustic anthropogenic disturbances can cause physiological stress in animals. Human-induced stress may be particularly problematic for birds as new technologies, such as drones, increasingly invade their low-altitude air space. Although professional and recreational drone usage is increasing rapidly, there is little information on how drones affect avian behavior and physiology. We examined the effects of drone activity on behavior and physiology in adult, box-nesting tree swallows (Tachycineta bicolor). Specifically, we monitored bird behavior during drone flights and in response to a control object and measured telomere lengths and corticosterone levels as indicators of longer-term physiological stress. We predicted that drone-exposed tree swallows would habituate behaviorally after multiple flights, but that telomeres would shorten more quickly and that baseline corticosterone levels would be altered. One significant and two strong, non-significant trends in behavioral assays indicated that adult swallows acted more aggressively towards drone presence compared to a control object, but were slower to approach the drone initially. Swallows were also more reluctant to use nest boxes during drone activity. Tree swallows habituated to drone presence as expected, although the rate of habituation often did not differ between drone-exposed and control groups. Contrary to our prediction, drone activity did not affect telomere length, corticosterone levels, body mass or fledging rates. Overall, our results indicate that a small number of short, targeted, drone flights do not impact tree swallow health or productivity differently than a non-invasive control object. Minor behavioral differences suggest that increasing the frequency of drone use could impact this species. We provide some of the first results addressing how drone activity alters behavioral, physiological and molecular responses to stress in songbirds. A better understanding of these impacts will allow ecologists to make more informed decisions on the use and regulation of new drone technologies.

Noise is an increasingly common component of the natural world, due in large part to human activity. Anthropogenic noise negatively impacts abundance, health, and reproduction in many songbird populations. A few studies have reported altered abundance at larger scales. But whether continental trends are being detected at banding stations, which also offer data on productivity and survivorship, is unknown. Further, it is not known whether localized trends correlate with population trends observed at larger scales. We used breeding season data from 1160 constant-effort banding stations (Monitoring Avian Productivity and Survivorship; MAPS) and a spatially explicit noise model to determine whether abundance and productivity were related to mean noise level or spatial heterogeneity (SD) in noise within a 1-km station radius for 72 passerine species. We also determined whether particular life history traits were predictive of noise responses, and compared continental results to those from local studies. Increasing mean noise level was associated with declines in abundance for 27.1% of species and productivity in 22.1% species. Increasing heterogeneity was associated with declines in abundance for 14.3% species and productivity in 14.7% species. The relationship between noise and abundance was not correlated with the relationship between noise and productivity, and acoustic and life history traits were not related to noise responses. Continental results were similar to localized data in 43.1% and 21.4% of species for abundance and productivity, respectively. Although some patterns differed between the local and continental scale, our results indicate that the MAPS banding dataset is capable of detecting noise-associated impacts on abundance and productivity. This is currently the only large-scale dataset capable of quantifying the relationship between noise and productivity in the continental USA, although other datasets exist elsewhere that may also contribute to our understanding of noise impacts at the larger scale.

Many songbird species have evolved multiple vocalizations, or repertoires, that function to communicate various biological signals. More diverse repertoires may have evolved in response to the effects of seasonal variation in habitat structure on signal transmission. Such changes in habitat necessarily occur for migrating species, but they also occur for resident species that occupy deciduous forests. The black-capped chickadee (Poecile atricapillus) possesses a chick-a-dee call and a fee-bee song, but the closely related boreal chickadee (P. borealis) lacks a song. Consistent with the habitat variability hypothesis, the black-capped chickadee possesses a larger repertoire and primarily occupies deciduous forests, whereas the songless boreal chickadee occurs more often in coniferous forests. We explored the ecological basis of this hypothesis by recording audio playbacks of two species in two habitat types during two seasons. Specifically, we played both songs and calls of the black-capped chickadee and calls of the boreal chickadee in deciduous and coniferous habitats, prior to and after leaf-out. We measured attenuation and degradation in re-recorded vocalizations. For black-capped chickadees, the song was less degraded than the call in post-leaf, deciduous forests. The boreal chickadee call attenuated more quickly in all treatments, but maintained its acoustic structure better than both black-capped chickadee vocalizations in coniferous forests. Our results support the hypothesis that variable habitats provided a seasonal transmission benefit for both song and call in the black-capped chickadee, but that the transmission benefit of song is lost in the less variant coniferous forests, which may underlie the absence of a song in the boreal chickadee.

The presence of conspecifics is an indicator of good habitat for a number of songbird species; a cue positively associated with territory selection. Thus, conspecific playback may be a cost-effective tool for attracting songbirds to particular, preselected sites of high-quality habitat. Previous studies have used conspecific playback to encourage the establishment of a single species; however, few have researched the potential for the simultaneous attraction of multiple species. Furthermore, empirical studies on the effect of song playback for nonfocal species are sparse. We investigated whether 6 migratory songbird species are more likely to establish nesting territories in response to multispecies playback. To evaluate the effect on the greater songbird community, we assessed the responses of 22 nonfocal species. Three of 6 focal species increased their use of areas near playback speakers, and none became less common. However, several nonfocal species were less likely to use playback sites. Phylogenetic comparison revealed that species closely related to playback species were those most likely to be affected. Our results suggest that conspecific attraction can be used to attract multiple songbird species simultaneously, but that its impact on nonfocal species should be considered before implementation.

Point counts are one of the most common ways of collecting data to determine the relative abundance of birds. Many studies and monitoring programs, including the North American Breeding Bird Survey, use relative differences in counts of birds to assess changes in abundance over time and space. Many factors influence whether relative differences in counts of birds between various environmental conditions are reflective of actual differences in bird density. A major assumption of relative abundance is that birds with different song frequencies and amplitudes are heard at the same distances in different environmental conditions. We compared sound transmission in forest habitats and along low-use forestry roads, and calculated detection radius for different species to test the assumption that differences in bird counts between forest interior and roadside locations reflect actual differences in bird abundance. A playback–recording experiment was used to broadcast sounds through forest interior, along...

Although it is known that animals attend to the vocalizations of others (referred to as eavesdropping), what has been missing, or at least left experimentally unproven, until now is whether animals can learn new associations between a signal and a threat. Here Magrath and colleagues (Current Biology, 25(15), 2047-2050, 2015) have for the first time conducted a field experiment that demonstrates just this: superb fairy-wrens learned to associate a novel vocalization with a predator.

SUMMARY Songbirds often modify elements of their songs or calls in particular social situations (e.g. song matching, flock convergence, etc.) but whether adult individuals also make vocal modifications in response to abiotic environmental factors (e.g. food availability) is relatively unknown. In the present study we test whether two different schedules of food reinforcement,fixed ratio continuous reinforcement and variable ratio partial reinforcement,cause adult black-capped chickadees to change the structure of their chick-a-dee calls. We also examine how these calls differ in two contexts:being alone versus when experiencing an alarming event. Wild-caught black-capped chickadees were housed in isolation to prevent social interaction and recorded weekly for seven weeks. Baseline recordings on week one show that calls given alone differed from those given during an alarming event in both note type composition and frequency (i.e. pitch). Calls also changed over time between birds on the two different schedules of reinforcement. In addition,birds on different reinforcement schedules responded differently during the two recording conditions. Our results suggest that call characteristics can be modified rapidly and may reflect abiotic environmental conditions. If call structure varies consistently with particular abiotic environmental conditions, much can be gained from bioacoustic analyses of calls from wild birds. However, vocal patterns must be consistent across dialects, and we must disentangle vocal changes due to the abiotic environment from those due to social interaction. Further research is needed from natural populations and across multiple regions.

Ascertaining the functions bird song requires information about when and where a song or, for males with multisong repertoires, songs are used. Because the need for and type of communication with mates and conspecifics changes with breeding stage and social context, detailed observations may reveal differential use of song or of different song types. Our objective was to examine the use, and determine the possible functions, of the two song types (primary and sustained) in the repertoire of male grasshopper sparrows (Ammodramus savannarum) by observing males throughout the breeding season and in different behavioral contexts in Madison County, Kentucky. For primary songs, rates varied among breeding stages and were highest before pairing, suggesting that primary song plays a role in mate attraction. However, male Grasshopper Sparrows continued to use primary songs after pairing, and likely functions include territory defense. The use of sustained songs also varied among breeding stages, with none uttered before pairing and rates highest during nest building and incubation. Male grasshopper sparrows also uttered more sustained songs when being observed (with one of us in their territories) then when not (neighboring males). These results suggest that sustained songs may serve to alert females to the presence of potential predators while simultaneously distracting such predators. Songs with such functions appear to be uncommon and have been reported in few other species.

Mounting evidence suggests that anthropogenic noise negatively impacts many wildlife species, including songbirds. One mechanism by which noise affects songbirds may be through acoustic obstruction to their systems of vocal communication. However, many species increase the amplitude or pitch of their vocalizations, which may partially mitigate the impact of high noise levels. When the amplitude of anthropogenic noise varies over time, such as near a moderate-use highway, short gaps between noise events may also provide an important opportunity for communication. But, whether songbirds adjust vocalization rates rapidly to avoid overlap with noise is unknown for most species. We used acoustic playback to expose songbirds to simulated road noise during the dawn chorus in otherwise quiet habitats. We measured vocalization rates under ambient conditions and during quiet gaps embedded within playback of road noise to assess whether a community of songbirds, and nineteen individual species, vocalize more regularly during noise gaps. There were no significant differences in community-wide acoustic output. Species-specific analysis revealed that only four species altered their vocal rates during quiet gaps in noise, but that the direction of the effect varied by species. Point count results revealed that birds generally remained on site for the duration of the experiment, suggesting that abandonment of noisy locations was unlikely to confound our results. In sum, increasing vocal output during short gaps in noise occurred in only a handful of species, perhaps contributing to the limited number of species that are found within noisy habitats.

Songbirds, with their reliance on acoustic communication, may be especially sensitive to potential population consequences of anthropogenic noise. Regional studies suggest that many species avoid noisy areas, and in some cases non-avoiding individuals experience reduced fitness. However, multiple studies of a species sometimes produce conflicting results, perhaps due to localized processes that overpower or exacerbate noise effects. Many studies also use abundance as an imperfect proxy for population persistence. To address these issues, we paired large published datasets—from the MAPs (Monitoring Avian Productivity and Survivorship) program and the U.S. National Parks Service noise map—to assess noise levels and bird demographics across the continental United States. We modeled effects of noise on songbird diversity, abundance, productivity, and physical condition (fat score), accounting for temporal and spatial variation. At the continental scale, diversity decreased with increasing noise, but other eff...

It is known that adult songbirds can modify the output and structure of their vocalizations in different behavioral contexts. However, whether changes in the abiotic environment (i.e., food availability) also affect vocal structure is less understood. Here we test whether the chick‐a‐dee calls of the black‐capped chickadee differ between birds on two different schedules of reinforcement (continuous and partial) and in two different behavioral contexts (singing alone and mildly alarmed by human intrusion). Our results reveal differences in the composition and pitch of chick‐a‐dee calls from birds in different behavioral contexts and on different schedules of reinforcement. However, calls from birds on the different schedules of reinforcement become more similar when evoked by human intrusion. We suggest that these results may represent differences in the energy dedicated to call production. If vocal structure varies consistently with changes to the abiotic environment, we may be able to detect environmental changes (i.e., warming and reduction in available forage) through analysis of vocal traits. While we demonstrate differences in call structure based on schedules of reinforcement, results from field studies in multiple regions will divulge whether these vocal changes are consistent and useful for analysis of abiotic conditions.