Human activities change the acoustic environment in many settings around the world. These changes are complex, as different anthropogenic sound sources create different acoustic profiles; therefore, some sound sources may have greater impacts on wildlife than others. Animals may adapt to these altered acoustic environments by adjusting their vocalizations. In the case of bird song, this may be achieved by adjusting the whole song, which may preserve the spectral and temporal relationships between successive syllables, or by adjusting components (syllables) within the song. Determining which syllables are adjusted may help to elucidate the mechanisms, benefits, and limitations of song plasticity. We examined the effects of conventional industrial infrastructure used to extract shallow natural gas and petroleum (natural gas compressor stations, generator-powered oil well pumpjacks, power grid–powered oil well screw pumps, and generator-powered oil well screw pumps), compared with quiet control sites, on 15 variables describing the acoustic properties of whole songs and syllables of Savannah Sparrows (Passerculus sandwichensis). Changes in acoustic properties varied with syllable and infrastructure type; most effects occurred at generator-powered screw pump sites, the loudest type of infrastructure that we studied. We found no effects of infrastructure on whole song variables, but song minimum frequency increased with ambient background noise. We found differing effects of infrastructure type on individual syllable types, with alterations in frequencies, tonalities, and syllable durations. This suggests that some syllables may be more plastic in their response than others, which may allow Savannah Sparrows to adapt their communication in altered acoustic environments.

The global spread of invasive species has created significant challenges for avian conservation. Introduced predators and pathogens have long been recognized for their direct negative effects on birds, but introduced amphibians can reach high densities on islands with no native amphibians, where they interact with native species. The coqui frog (Eleutherodactylus coqui), introduced to the Hawaiian Islands in the late 1980s, could have significant impacts on birds because it is fully terrestrial and achieves high densities. Coquis have been hypothesized to compete with native birds for invertebrate prey, but could also serve as a novel food resource for birds that consume small vertebrates. To test whether coquis measurably affect bird abundance, we conducted point counts of birds in coqui-invaded and adjacent uninvaded plots across 15 sites on the island of Hawaii, USA. We used N-mixture models to estimate the effect of coqui presence and density on the abundances of both native and nonnative birds, while controlling for possible habitat differences between plots with and without coquis. We found that coquis were associated with ∼35% higher abundance of nonnative birds in general, and more specifically generalist birds that sometimes consume small vertebrates. We suggest that generalist birds increase in abundance with coquis primarily because coquis serve as an abundant food resource. While 4 native bird species co-occurred with coquis, native bird abundance (20% of our total observations) did not show a difference across coqui-invaded and uninvaded plots. Coquis do not appear to be important competitors with native birds in Hawaii, but the frogs are associated with increased abundances of some nonnative birds, which could induce undesirable ecosystem impacts.

The seasonal phenology of latitudinal movements is one of the key life-history traits of migratory birds. We used quantile regression to examine long-term changes in the timing of spring and autumn migration in 5 species of migratory passerine birds captured at a banding station in northern California, USA, over a 22 yr period from 1987 to 2008. Our 5 study species included 3 short-distance migrants, Pacific-slope Flycatcher (Empidonax difficilis), Orange-crowned Warbler (Oreothlypis celata), and Wilson's Warbler (Cardellina pusilla); and 2 long-distance migrants, Swainson's Thrush (Catharus ustulatus) and Yellow Warbler (Setophaga petechia). Median timing of migration advanced in spring for 2 of the 5 species (−2.5 days decade⁻¹) but was delayed during autumn migration for 3 of the species ( 2.9 days decade⁻¹). The duration of the migration period also became compressed in some species but more protracted in others. We tested whether annual variation in migration timing was related to 3 indices of regional climatic conditions: the Pacific–North American index, multivariate El Niño–Southern Oscillation index, and North Atlantic Oscillation index. Climate indices explained relatively little of the variation in migration timing (r² < 0.35), but advances in spring migration and delays in autumn migration were associated with warm, wet conditions during positive phases of the climate indices. The strongest effects of climatic conditions on migration timing were found among short-distance migrants, with the largest changes in timing due to variation in the El Niño–Southern Oscillation and Pacific–North American indices. Linkages between the timing of movements and climatic conditions indicate that passerine birds on the Pacific coast exhibit phenotypic plasticity in their migration timing, but future studies based on experimental methods are needed to test alternative ecological mechanisms.

Shorebird populations face increasing challenges as rising sea levels and growing human populations constrain their breeding habitats. On recreational beaches, the nesting season often coincides with a season of high visitor use, increasing the potential for conflict, which may negatively influence beach-nesting shorebird species. We designed a field experiment to study the responses of nesting American Oystercatchers (Haematopus palliatus) to off-road passenger vehicles (ORVs) at Cape Hatteras and Cape Lookout National Seashores in North Carolina, USA. We used continuous video and heart rate recordings to assess changes in the behavior and physiology of incubating oystercatchers. We conducted driving experiments affecting 7 nesting pairs in 2014 and 19 nesting pairs in 2015, between April and July of each year. Experimental treatments were repeated throughout the incubation period for each nest. Although responses were highly variable within and among pairs, paired randomized permutation tests indicated that, overall, oystercatcher pairs spent a greater proportion of time with their heads up and exhibited slower heart rates during driving treatments. Pairs also left their nests more frequently and attended their nests for a lower proportion of time during driving treatments, although these responses diminished over time. Higher nest attendance and lower departure rates late in incubation may have reflected a stronger attachment to nests closer to hatching or habituation to the driving treatment, although individuals continued to exhibit physiological responses to passing vehicles throughout incubation. Beach-nesting birds may benefit from reduced vehicle traffic at their nesting sites, allowing parents to spend more time attending the nest and less time on defensive behaviors.

Cooper's Hawks (Accipiter cooperii) have been extending their breeding range into urban areas, prompting questions about the relative importance of cities to the demography and conservation of these raptors. A key unanswered question is how urban subpopulations interact with their precedent exurban subpopulations. Two general models have been proposed to describe relationships among subpopulations in a metapopulation: (1) source–sink, where immigrants from sources sustain sinks; and (2) balanced dispersal, where dispersal is proportionally equal among subpopulations. I evaluated whether either of these models predict metapopulation dynamics of urban and exurban Cooper's Hawks in central New Mexico using demographic data in a Bayesian integrated population model. All urban female Cooper's Hawks began breeding in their first year; 69% settled at nests in the urban subpopulation and 31% emigrated and settled in an exurban subpopulation. The high rate of female emigration was likely because of a shortage of breeding urban males, caused by a 1 yr delay in male age-at-first-breeding. Emigration exceeded immigration by nearly 30%, making a balanced-dispersal model implausible. Although the urban subpopulation was a source, the primary recipient subpopulation was not a sink; urban emigrants appeared to have a competitive advantage obtaining exurban nest sites. High urban winter prey abundance supported year-long residency among urban female Cooper's Hawks, whereas nearly all exurban females migrated. Resident urban females that emigrated settled on exurban nesting territories before migrants returned, and thus without direct competition from them. Previous metapopulation models do not incorporate the concept that differences in dispersal behavior between subpopulations can drive dispersal dynamics in a metapopulation. These findings provide further evidence that patch dynamics in a metapopulation can be complex, and may be governed by factors other than just demographic rates and connectivity.

The ability to locate high-quality stopover habitat has fitness implications for migrating landbirds, and alteration of stopover habitats due to human land-use change, including the introduction of nonnative plants, has been identified as a conservation concern. We tested whether the use and selection of shrublands dominated by exotic plants differed from that of native-dominated shrublands. Specifically, we compared capture rates, transfer rates between habitats, within-foraging-range habitat selection, and food items of Swainson's Thrushes (Catharus ustulatus) and Gray Catbirds (Dumetella carolinensis) between exotic- and native-dominated shrublands in Michigan, USA, during fall migration of 2012 and 2013. Capture rates were >20% higher for thrushes and >250% higher for catbirds in native shrubland. Capture–recapture data showed that birds moved from exotic to native shrubland at higher rates than vice versa. For radio-tagged thrushes and catbirds, native shrubland was ∼30% more likely to be used than expected by land cover at the within-foraging-range scale. Thrushes, but not catbirds, avoided exotic shrubs within their foraging ranges. Native Lindera benzoin fruit was >50% more likely to be found in fecal samples from both bird species in native-dominated shrubland than in exotic-dominated shrubland, and was the predominant food item in the former habitat type. Collectively, our results suggest that fall migrating Swainson's Thrushes and Gray Catbirds select, and hence occur at higher densities in, predominantly native shrublands rather than exotic-dominated shrublands. One mechanism for this pattern may be their preference for certain native fruits, such as L. benzoin. Our results suggest that native shrubland may be an especially important stopover habitat for frugivorous birds during fall migration.

Management of reed beds primarily includes controlling water levels and removing vegetation by mowing, burning, or grazing. Although recent studies have demonstrated increased diversity and abundance of wetland specialists after reed bed management, documenting demographic benefits to individual species would add additional support to the advantages of appropriate management. Here, we explore the effects of reed management on the philopatry of Great Reed Warblers (Acrocephalus arundinaceus) over 7 yr. Reed beds were managed in the winter by occasional burning at mining ponds and large canals, infrequent burning in marshes, and frequent mowing of small canals. Based on resightings and recaptures of 1,243 adult and 1,428 nestlings individually marked at 57 sites in 6 different reed habitats, we built Cormack-Jolly-Seber models to estimate the apparent annual survival and encounter probabilities of birds banded as nestlings or as adults. Apparent survival varied in time for both age groups and both sexes, suggesting annual fluctuations in survival, whereas encounter probability remained constant across years. The encounter probability of birds banded as juveniles was higher in reed beds with shallower water. The encounter probability of birds banded as adults was higher in reed beds with deeper water for females, and strongly increased with variation in reed management and less strongly with variation in water depth for males. We also found that the few returning juveniles displayed strong philopatry to the reed habitat occupied in their first breeding season. Our study provides evidence that reed management influences the return rates of juveniles and adult males and females in different ways. Spatially variable reed management by mowing or burning should be applied and water of varying depths should be maintained to maximize return rates of Great Reed Warblers.

We used a broad-scale sampling design to investigate spatial patterns in occupancy and breeding success of territorial pairs of Golden Eagles (Aquila chrysaetos) in the Diablo Range, California, USA, during a period of exceptional drought (2014–2016). We surveyed 138 randomly selected sample sites over 4 occasions each year and identified 199 pairs of eagles, 100 of which were detected in focal sample sites. We then used dynamic multistate modeling to identify relationships between site occupancy and reproduction of Golden Eagles relative to spatial variability in landscape composition and drought conditions. We observed little variability among years in site occupancy (3-yr mean = 0.74), but the estimated annual probability of successful reproduction was relatively low during the study period and declined from 0.39 (± 0.08 SE) to 0.18 (± 0.07 SE). Probabilities of site occupancy and reproduction were substantially greater at sample sites that were occupied by successful breeders in the previous year, indicating the presence of sites that were consistently used by successfully reproducing eagles. We found strong evidence for nonrandom spatial distribution in both occupancy and reproduction: Sites with the greatest potential for occupancy were characterized by rugged terrain conditions with intermediate amounts of grassland interspersed with patches of oak woodland and coniferous forest, whereas successful reproduction was most strongly associated with the amount of precipitation that a site received during the nesting period. Our findings highlight the contribution of consistently occupied and productive breeding sites to overall productivity of the local breeding population, and show that both occupancy and reproduction at these sites were maintained even during a period of exceptional drought. Our approach to quantifying and mapping site quality should be especially useful for the spatial prioritization of compensation measures intended to help offset the impacts of increasing human land use and development on Golden Eagles and their habitats.

Choosing a high-quality mate contributes to increased reproductive success in birds. Females assess quality in males, in part, via condition-dependent signals such as songs and plumage. The production of these signals of quality can be disrupted by environmental stressors, including toxic pollutants such as mercury. Mercury affects song, plumage, bill color, and courtship behaviors in male birds, but the effect of these changes on female mate choice is unknown. By affecting the condition-dependent signals that females use to assess quality, mercury could alter males' attractiveness to females. We used mate choice of female Zebra Finches (Taeniopygia guttata) to determine if male attractiveness to females is affected by lifetime exposure to mercury. Males were either exposed to dietary mercury or left unexposed and then assessed by unexposed females in 3 types of mate preference tests: song-playback phonotaxis (preference for audio recordings of mercury-exposed or unexposed males' songs); 2-choice social association preference (simultaneous choice between mercury-exposed or unexposed males in adjacent cages); and pairing (opportunity to pair with either a mercury-exposed male or unexposed male in an aviary). In song-playback phonotaxis and social association tests, females did not spend more time near songs or males of one treatment over the other, despite measurable differences between songs. In an aviary pairing test, females were equally likely to pair with males of either treatment. While mercury exposure is known to reduce production of offspring in Zebra Finches and other birds, our results suggest that captive female Zebra Finches may not be incorporating mercury-induced variation in male traits into their mate choice decisions. If female birds living in contaminated environments experience fitness losses as a result of potentially poor mate choice decisions, then females may eventually respond to this sexual selection pressure by including toxicant-mediated trait variation in their quality assessment mechanisms.

The potential for wind energy facilities to affect species of grouse in the grasslands of the Great Plains of North America is a conservation concern. Communication by male Greater Prairie-Chickens (Tympanuchus cupido pinnatus) is essential for lek mating displays and includes low-frequency vocalizations that could be disrupted by wind turbine noise. We studied the effects of wind turbine noise on the boom, cackle, whine, and whoop vocalizations of male Greater Prairie-Chickens recorded at 14 leks located 703 m to 23 km away from a wind energy facility near Ainsworth, Brown County, Nebraska, USA, in 2013 and 2014. First, we assessed ambient sound levels at our study sites. Wind turbine noise contributed to the soundscape; leks <1,000 m from wind turbines had higher levels of ambient sound than expected on the basis of recordings obtained at remote locations. Our second objective was to determine whether the acoustic characteristics of the 4 vocalizations recorded near the wind energy facility differed from those recorded farther away. At leks within 1,000 m of the wind energy facility, boom and whoop sound pressure levels were higher (boom 2% higher; whoop 5% higher), boom duration was 3% shorter, whine fundamental frequency was 11% higher, and biphonations in cackle vocalizations occurred 15% less often. These differences suggest that male Greater Prairie-Chickens adjust the acoustic properties of their vocalizations in response to the sounds generated by turbines at wind energy facilities. The effect of the adjustments reported here on the mating success of males near wind energy facilities remains to be determined.

Globally, riparian ecosystems are in decline due to anthropogenic modifications, including damming. Reduced frequency and altered timing of flood events decreases sandbar deposition, which reduces habitat for sandbar-breeding birds, including the threatened Piping Plover (Charadrius melodus). In response to limited breeding habitat and small populations, the U.S. Army Corps of Engineers constructed 255 ha of sandbar habitat on the Missouri River, USA, from 2004 to 2009. During the breeding seasons of 2010 and 2011, historically high flows resulted in the creation of 1,046 ha of suitable sandbar habitat on the Missouri River. We compared the demographic responses of Piping Plovers to this anthropogenic and natural habitat creation. We found that demographic parameters, including nest success (x̄_preflood = 0.45 ± 0.02 SE vs. x̄_postflood = 0.74 ± 0.02 SE), prefledging chick survival (x̄_preflood = 0.39 ± 0.09 SE vs. x̄_postflood = 0.65 ± 0.03 SE), and hatch-year survival (x̄_preflood = 0.16 ± 0.03 SE vs. x̄_postflood = 0.46 ± 0.03 SE), were consistently higher on the flood-created habitat than on the engineered habitat, leading to population growth after the flood. These differences were related to increased sandbar habitat, low nesting densities, and decreased nest and chick predation. As ecosystems are increasingly altered, ecologists seldom have the opportunity to make appropriate comparisons between managed and natural ecosystem processes. Our results suggest that management intervention may not be an appropriate substitute for natural ecosystem processes in riparian ecosystems.

Much of our understanding of en route landbird habitat use comes from research performed at local scales, ignoring effects at larger spatial scales. We used a multiscale approach to investigate stopover habitat use by landbirds using transect surveys in 68 forested sites in southwestern Michigan, USA, during the springs of 2002 and 2003. We modeled relationships of bird density and arthropod abundance with broad-scale spatiotemporal factors (year, day of year, geographic location) and local landscape (forest composition and structure, presence of open water) as well as site-scale factors (bird density and arthropod abundance, which exchanged roles as predictor and response variables). We found migrant densities to be most influenced by fine-scale factors, such as the abundance of other avian taxa and substrate arthropods, followed by broader-scale factors, such as forest structure and location, within the local and broader surrounding landscape. We found that migrant habitat associations either did not directly match or were weakly associated with the availability of riparian or lacustrine water habitats at a local scale, even though our results suggested that birds using these habitat cues would have encountered more arthropods. Rather than finding indirect measures of food abundance—such as distance to a water source or forest cover at the landscape scale—important, our models best explained bird density by a direct relationship with site-scale food resources. Thus, the scale at which migrants demonstrate habitat selection appears to be influenced by proximate mechanisms such as high-quality habitat availability and the presence of large ecological features within the landscape. Not only do factors operating at multiple scales influence how birds use habitats, but scale also influences how we interpret research findings, in turn influencing conservation decisions.

Some statistics in “Biochemical and clinical responses of Common Eiders to implanted satellite transmitters” were miscalculated due to missing data. We provide corrected values for the affected variables. Corrected data did not affect the conclusions of the paper.

Advancement in timing of important life history events for birds due to climate change presents conservation and monitoring challenges. Song and other vocal activity are strong indicators of avian phenology because they correspond to territorial defense and mate attraction during the breeding season. We combined data from 2 projects using point counts and automated sound recorders to survey passerines during the breeding season in northern California, USA (553 sites, 2009–2011). We used multi-species occupancy modeling to estimate how detection probability based on vocalizations varied over the course of the breeding season. We estimated dates of peak vocal activity, which we reasoned were indicative of reproductive phenology. We demonstrated a strong unimodal relationship between vocal activity and survey date for 8 focal species for which average detectability peaked on June 21 (90% CI: June 19–June 22). Although we found no difference in peak dates of average detectability for migrants vs. residents, the variability of this estimate was lowest for Neotropical migrants compared to residents and elevational migrants. This finding supports previous research suggesting that long-distance migrants may be less flexible in adapting their phenology and more vulnerable to climate change. For an 80% power standard, we found that repeating our level of survey effort on an annual basis would allow detection of an advancement of average peak vocal activity by as small as 2.2 days over 10 yr for the focal species. We could detect smaller average shifts of 0.8 day decade⁻¹ for this group or 1.6 days decade⁻¹ for all passerines over 20 yr. Monitoring vocal phenology of birds through occupancy modeling of survey data from the breeding season is an efficient approach to assessing climate change impacts because species occupancies and measures of community-level diversity can be simultaneously estimated.

The Marbled Murrelet (Brachyramphus marmoratus) is federally threatened in part of its range in western North America. Information on density and productivity is important for managing populations. Over an 18-yr period, we monitored murrelet density and productivity ratios during the breeding season along 170 km of shoreline of the San Juan Islands, Washington, USA. While murrelets occur throughout the coastal marine waters of Washington, the San Juan Islands support higher densities of murrelets during the breeding season than most other areas. From 1995 to 2012, the average density of adult murrelets declined significantly from 11.16 to 5.76 murrelets km⁻², a decline that mirrored large-scale at-sea surveys in Washington. Despite this consistent and ominous decline in overall murrelet density, the density of juvenile murrelets and murrelet productivity ratio (juveniles:adults) did not decline over this time period. Thus, the declining density of murrelets in the San Juan Islands was due to declines in adult murrelets only, not juveniles. Annual estimates of overall murrelet density were positively correlated with winter El Niño Southern Oscillation (ENSO) indices. We estimated that, on average, 6,605 (± 2,531 SD) murrelets occurred during surveys annually, confirming that the San Juan Islands contain some of the most heavily used marine areas in the portion of the U.S. range in which murrelets are threatened. In ENSO years, numbers increased to >8,500 birds. Heavy use of the San Juan Islands in ENSO years suggests that this area may provide refugia marine habitat for murrelets when prey availability along the outer Pacific Coast is poorer than usual.

Land use restrictions imposed by the Endangered Species Act may create conflict, affecting conservation on private lands. In 1995, the Safe Harbor program (hereafter, ‘Safe Harbor’) was initiated to alleviate concerns of private landowners about conservation of imperiled species. The inaugural program targeted endangered Red-cockaded Woodpeckers (Picoides borealis; hereafter, ‘RCW') in the North Carolina Sandhills, USA. Landowners enrolled in the Safe Harbor select management actions to enhance habitat for existing populations, but incur no additional responsibilities for increases in populations. Despite the relevance for conservation, the benefits of Safe Harbor remain largely unknown. Here, we evaluate the effects of Safe Harbor on RCWs in the North Carolina Sandhills. Between 1980 and 2014, we monitored 55 RCW territories (30 Safe Harbor, 25 control). Following the initiation of Safe Harbor, the probability of territory abandonment on control properties increased by ∼14% over a 19-yr period, while it remained constant on Safe Harbor properties. This could have been due to more Safe Harbor properties (87%) than control properties (68%) receiving artificial cavities that offset cavity losses. Following the initiation of Safe Harbor, the laying date on Safe Harbor properties advanced 16.1 days over a 19-yr period, compared with 11.6 days on control properties. Enrollment in Safe Harbor was not related to other measures of breeding performance, likely due to variation in habitat management across properties. While Safe Harbor clearly alleviates conflict over conservation, other effects depend on management actions. We encourage evaluations of existing similar programs to determine their efficacy.

Changes in climate, vegetation, and land use are recognized as important drivers of changes in the distribution and abundance of wildlife. However, the behavioral and demographic mechanisms through which these changes affect populations have received less attention. Identifying these mechanisms is an important component of predicting the impacts of increasing environmental change. We used 30 yr of nest monitoring data at a study site where White-crowned Sparrow (Zonotrichia leucophrys) breeding density declined 85% to evaluate factors influencing habitat selection and reproductive success. Rapid secondary plant succession occurred at our study site, but the rate of change was faster in some areas than others. White-crowned Sparrows exhibited strong patterns of nest site selection, preferring open shrub vegetation and avoiding forest. As a result, many parts of the study area that were used for nesting early in the study period were no longer occupied by the end of the study period. Over the course of the study, both the weather conditions and the vegetation structure and composition around nests varied. Across the range of occupied habitat, we found no effect of vegetation structure on reproductive success. We also found no support for effects of temperature and rainfall on nest survival, and only weak and inconsistent effects of temperature on clutch size and the number of fledglings per nest. These results indicate that vegetation change drove changes in the nest sites used through habitat selection, and that habitat selection appeared to ameliorate any potential negative effects of vegetation change on per capita reproductive success. Hence, the population's response to rapid vegetation change was driven, at least in part, by site selection, rather than by a decline in reproductive success. In light of increasing environmental variation, it will be important to partition the effects of environmental change on habitat use and reproductive success to predict population viability and extinction risk.