Anthropogenic environmental changes are leading to habitat loss and degradation, driving many species to extinction. In this context, habitat models become increasingly important for effective species management and conservation. However, most habitat studies lack replicated study areas and do not properly address the role of nonstationarity and spatial scales in determining factors that limit species occurrence under different environmental settings. Here we provide an optimized multi-scale framework for analyzing habitat selection of the threatened Mexican Spotted Owl (Strix occidentalis lucida) between 2 meta-replicated study areas: the Sacramento Mountains, New Mexico, and the Mogollon Plateau, Arizona. The optimized scales of habitat variables strongly differed between the 2 study areas. Percent cover of mixed-conifer was more strongly associated with the relative likelihood of Mexican Spotted Owl occurrence in the Sacramento Mountains than in the Mogollon Plateau. Topographic covariates strongly explained variance in the habitat model in the Mogollon Plateau, but not in the Sacramento Mountains. Topographically constrained habitat availability may be affecting the relative likelihood of owl occurrence in the Mogollon Plateau, but not in the Sacramento Mountains. In the Sacramento Mountains, suitable habitat and owl distributions show dissimilar spatial autocorrelation patterns, indicating that the relative likelihood of occurrence may be influenced by factors in addition to habitat. Owl distribution shows a periodic spatial pattern, suggesting that the relative likelihood of owl occurrence in the Sacramento Mountains might be influenced by territoriality. Differences in habitat relationships between the 2 study areas suggest that management strategies should be tailored to local conditions. This study underscores the advantage of scale optimization and replicated studies in analyzing nonstationary habitat selection.

Rapid development of wind energy facilities in the Great Plains of North America has raised concerns regarding their potential negative impact on the nesting ecology of Greater Prairie-Chickens (Tympanuchus cupido pinnatus). We investigated the effects of a pre-existing, 36-turbine wind energy facility on nest site selection and nest survival of Greater Prairie-Chickens in the unfragmented grasslands of the Nebraska Sandhills, USA. In 2013 and 2014, we monitored 91 nests along a 24-km disturbance gradient leading away from the wind energy facility. We found little evidence of an effect of the wind energy facility on Greater Prairie-Chicken nest site selection and nest survival. Instead, we found that the primary drivers of nest site selection and nest survival were related to landscape and habitat factors. Greater Prairie-Chickens avoided nesting near roads, with 74% of Greater Prairie-Chickens selecting nest sites >700 m from roads. Greater Prairie-Chickens selected nest sites with more than twice the visual obstruction and residual standing dead vegetation of random points. Our results suggest that small wind energy facilities, such as the facility in our study, may have little effect on Greater Prairie-Chicken nest site selection and nest survival. We suggest that livestock grazing and other grassland management practices still have the most important regional effects on Great Prairie-Chickens, but we caution future planners of wind energy facilities to account for the potential negative effect of roads on nest site selection.

Although bird population declines associated with land degradation are common, the initial response of organisms to rapid human-induced environmental change is usually behavioral. Reductions in seed availability due to cattle grazing may trigger diet switching in seed-eating birds, but empirical examples of such behavior are lacking. We asked whether cattle grazing changed the composition and reduced the size of seed reserves, and whether seed shortage caused diet shifts in 4 species of seed-eating birds wintering in the central Monte Desert, Argentina. We assessed the soil seed bank composition and the granivorous fraction of each species' diet. Digestive tract or crop contents were obtained by using the flushing method on individuals captured with mist nets, and seeds were sorted and assigned to 1 of 3 functional groups (small grass seeds, large and medium-sized grass seeds, or forb seeds). Cattle grazing reduced the abundance of the preferred large and medium-sized grass seeds by 60–90%. The grass-seed specialists Many-colored Chaco Finch (Saltatricula multicolor) and Ringed Warbling-Finch (Microspingus torquatus) did not change their diets in grazed areas, but the expanding specialists Common Diuca-Finch (Diuca diuca) and Rufous-collared Sparrow (Zonotrichia capensis) incorporated increased proportions of small grass seeds as well as forb seeds into their diets. These results were correctly predicted from species-specific differences in feeding flexibility previously established in cafeteria experiments. Based on species-specific diet composition, the energy reward of seeds by unit mass consumed decreased moderately (5–21%) in the grazed sites for S. multicolor, M. torquatus, and D. diuca. Starch content was similar between grazing conditions for all 3 birds. Although such deficits might be compensated for by a slight increase in absolute mass of seeds or alternative food items consumed in degraded lands, substantial reduction in the availability of grass seeds may reduce the capacity of degraded lands to support specialist granivorous birds.

Hybridization between species that do not normally interbreed has increased due to human impacts on natural environments, such as habitat alteration or introductions of nonnative species. In particular, the introduction of Mallards (Anas platyrhynchos) globally has led to hybridization with many duck species. In the southeastern United States, hybridization with Mallards is a potential threat to the genetic identity of Mottled Ducks (A. fulvigula), a nonmigratory, coastal duck species. Hybridization between Mallards and Mottled Ducks has been examined in South Carolina and Florida, but not extensively in the remaining part of the Mottled Duck range. Mottled Ducks introduced into South Carolina show considerable admixture with Mallards, whereas in Florida, the hybridization rate between Mallards and Mottled Ducks is ∼9%. Given these results, hybridization in the western Gulf Coast region is of potential concern and should be examined to determine the potential impact on the Mottled Duck lineage. In this study, we examined hybridization in the western Gulf Coast region using 36 microsatellite loci and 405 ducks consisting of putative Mottled Ducks (n = 319), Mallards (n = 76), and hybrids (n = 10). Overall, genetic analyses revealed levels of hybridization of ∼5–8%, with more individuals genetically assigned as hybrids from birds putatively identified as Mallards (5/76 and 14/76 in STRUCTURE and INSTRUCT, respectively) than as Mottled Ducks (14/319 in both programs). These data suggest that hybridization rates in the western Gulf Coast region are lower than those in Florida. However, projected coastal marsh loss in Texas and Louisiana may drive Mottled Ducks into urban wetland areas, an outcome that may increase contact between Mottled Ducks and Mallards and could result in similar levels of hybridization to those observed in Florida, where Mottled Ducks occupy urban and suburban habitats. Regular monitoring will help to determine future trends in levels of hybridization.

Movement behavior and its relationship to habitat provide critical information toward understanding the effects of changing environments on birds. The eastern North American population of Golden Eagles (Aquila chrysaetos) is a genetically distinct and small population of conservation concern. To evaluate the potential responses of this population to changing landscapes, we calculated the home range and core area sizes of 52 eagles of 6 age–sex classes during the summer and winter seasons. Variability in range size was related to variation in topography and open cover, and to age and sex. In summer, eagle ranges that were smaller had higher proportions of ridge tops and open cover and had greater topographic roughness than did larger ranges. In winter, smaller ranges had higher proportions of ridge tops, hillsides and cliffs, and open cover than did larger ranges. All age and sex classes responded similarly to topography and open cover in both seasons. Not surprisingly, adult eagles occupied the smallest ranges in both seasons. Young birds used larger ranges than adults, and subadults in summer used the largest ranges (>9,000 km²). Eastern adult home ranges in summer were 2–10 times larger than those reported for other populations in any season. Golden Eagles in eastern North America may need to compensate for generally lower-quality habitat in the region by using larger ranges that support access to adequate quantities of resources (prey, updrafts, and nesting, perching, and roosting sites) associated with open cover and diverse topography. Our results suggest that climate change–induced afforestation on the breeding grounds and ongoing land cover change from timber harvest and energy development on the wintering grounds may affect the amount of suitable habitat for Golden Eagles in eastern North America.

Areas of northern California, USA, have been identified as quality habitat for an expanded California Condor (Gymnogyps californianus) Recovery Program. Nonetheless, lead poisoning continues to complicate California Condor recovery efforts within their current range and threatens the viability of future propagules. Therefore, background levels of lead and other contaminants should be assessed as part of a feasibility analysis to determine the efficacy of expanding the Recovery Program into northern California. A California-wide ban on the use of lead ammunition for hunting, scheduled to go into effect in 2019, coupled with hunter outreach programs aimed at reducing the use of lead ammunition, may present new opportunities for California Condor recovery in this region. As such, we captured and studied 2 surrogate species, Common Ravens (Corvus corax) and Turkey Vultures (Cathartes aura), in coastal and near-coastal habitats of northern California to examine relationships between contaminant (lead, mercury, zinc, and copper) exposure relative to distance from the coast (vultures and ravens), age (vultures and ravens), and hunting season (ravens only). Although blood lead concentrations were relatively low throughout our study area for vultures (median = 5.99 μg dL⁻¹, n = 137), median blood lead concentrations of ravens captured during the hunting season (6.4 μg dL⁻¹, n = 10) were almost 6-fold higher than those of birds captured during the nonhunting season (1.1 μg dL⁻¹, n = 17). In addition, for both species, blood concentrations of mercury decreased with increasing distance from the coast, while blood concentrations of lead increased. Given the significant increase in blood lead concentration in ravens during the hunting season, we believe that pervasive exposure to lead demonstrates a risk facing potential propagules of California Condors throughout the species' historical range.

Many North American landbird populations have declined in recent decades, including those that occupy Western forest habitats. Long-term monitoring of abundance and vital rates allows us to detect species and habitats of concern, and to identify potential management actions. Here, we analyze capture data from a regional network of 10 banding sites in the Klamath-Siskiyou Bioregion, USA, to examine demographic trends for 12 Western forest bird species from 2002 to 2013. Adult abundance declined significantly in some breeding populations of Audubon's Yellow-rumped Warbler (Setophaga coronata auduboni) and Purple Finch (Haemorhous purpureus), and near-significantly in Oregon Dark-eyed Junco (Junco hyemalis oreganus). We observed significant declines in productivity of the Purple Finch and Spotted Towhee (Pipilo maculatus). Black-headed Grosbeaks (Pheucticus melanocephalus) and Yellow-breasted Chats (Icteria virens) increased significantly in adult abundance, but with variation among sites. Productivity in one year was positively correlated with adult abundance in the following year for only one species, suggesting that local productivity may not be the proximate demographic cause of population change. Trends in adult abundance were generally heterogeneous across the landscape, while trends in productivity were more consistent among sites. Ten of 12 bird species exhibited similar or more positive trends in the Klamath-Siskiyou Bioregion than in the larger Pacific Northwest region as measured by Breeding Bird Survey data. Data from long-term banding sites that include productivity indices and breeding status of adults can provide important supplementary information to other long-term monitoring data and help to generate hypotheses regarding proximate demographic causes of local population trends. Future studies using regional networks of banding sites may begin to elucidate source–sink dynamics and the scale at which they operate, a topic with implications for species conservation.

Songbirds are under strong pressure to choose nest locations that reduce the risk of nest predation and, as such, are expected to use a variety of information sources to guide decisions about nest sites. The activity patterns of potential predators in the local vicinity should be one especially important source of information, although this may vary in urban ecosystems with altered predator–prey relationships. We examined the extent to which predator activity was associated with the nest distribution and survival of Northern Cardinals (Cardinalis cardinalis) and Acadian Flycatchers (Empidonax virescens) in 13 riparian forests situated across a gradient of urbanization in central Ohio, USA, in 2008–2010. We focused on a suite of diurnal predators that was responsible for >70% of songbird nest depredations in our study system. By overlaying nest locations of cardinals (n = 334) and flycatchers (n = 60) on predator utilization distributions created from mapped predator locations at each site, we determined the corresponding probability of predator use for each site, year, and nest location. The amount of urbanization surrounding sites did not predict nest survival nor relationships between nest placement and nest predator activity. Instead, predator activity better explained patterns of nest distribution and survival. Cardinals nested in areas of high use by avian predators (especially Brown-headed Cowbird (Molothrus ater)), but nest survival only declined when these areas also received high use by mammalian predators. The distribution of flycatcher nests was unrelated to predator activity, but nest survival declined where avian predator activity was high and mammalian predator activity was low. Although predator movements at local scales predicted nest survival, our findings provided no evidence that cardinals and flycatchers used that information to select nest sites. Further examination of spatiotemporal variation in the use of predator cues by breeding songbirds is needed to elucidate patterns of information use in songbird nest-site selection, particularly in urban ecosystems.

In the first sentence of the fifth paragraph of the Discussion, the authors incorrectly stated the relationship between logging and territory occupancy. The sentence should read instead: “Logging was associated with occupancy in only one study area (Eldorado), where it unexpectedly had a negative association with territory extinction."

Golden-winged Warbler (Vermivora chrysoptera) populations in the Appalachian Mountains region of North America are imperiled, warranting species-specific conservation. However, management for Golden-winged Warblers can affect both early-successional and forest species, many of which are also declining in the region. We conducted point counts in sites representing a range of successional stages within the Golden-winged Warbler's breeding range in West Virginia, USA, during 2008–2015. We identified plausible models of Golden-winged Warbler density using covariates at 4 spatial scales representing annual dispersal (5-km radius), extraterritorial movement (1.5-km radius), intraterritorial movement (100-m radius), and local resource utilization (11.3-m radius). Golden-winged Warbler density peaked at an intermediate elevation at the 1.5-km radius scale, but was negatively associated with 100-m radius minimum elevation. Density was positively associated with 100-m radius shrubland cover. Southerly latitudes were associated with higher densities when modeled alone, but there was no association when controlling for other covariates. We then examined the relationship between covariates from these plausible models and avian community structure using canonical correspondence analysis to assess the value of Golden-winged Warbler conservation for the broader avian community. We identified 5 species likely to benefit from management for Golden-winged Warblers and 21 species likely to be affected positively or negatively to varying degrees depending on their affinity for early-successional vegetation communities. Golden-winged Warblers were plotted higher along the 100-m shrubland cover gradient than any other bird species, suggesting that they may be the most shrubland area–sensitive songbird in our study area. However, the species also requires heavily forested landscapes. Therefore, a species-specific conservation strategy that balances shrubland (patches of 9–13 ha in size, comprising 15% of the landscape) and contiguous forest area (≥75% of the landscape) could concurrently meet the needs of Golden-winged Warblers and the 26 other species identified.

Winter distribution and resource use of animals is driven by myriad interacting biotic and abiotic factors. Urban areas provide sanctuaries from hunting for game animals and may have thermal benefits during winter through reduced thermoregulatory costs. We deployed cellular GPS transmitters affixed to neck collars of 41 Canada Geese (Branta canadensis) in the Greater Chicago Metropolitan Area (GCMA) of northeastern Illinois, USA, to determine habitat selection and survival during autumn and winter. Canada Geese selected green spaces (59.8%) in greater proportion than available (14%), but they also regularly used industrial urban habitats such as rooftops and rail yards (11.3%), which has not been previously reported. Use of green spaces (−55.8%) decreased and use of industrial urban ( 11.4%), riverine ( 23.8%), and deep-water habitats ( 140.7%) increased as temperatures dropped below the lower critical temperature for Canada Geese (i.e. the temperature at which increased thermoregulatory costs are incurred to maintain core body temperature). Most Canada Geese (85%) remained within the GCMA throughout winter, and none made foraging flights to agricultural fields within or outside of the urban area. Seasonal survival was considerably greater (S = 1.0) for geese that remained within the GCMA than those that left (S = 0.48) during winter. High survival, use of nontraditional habitats (e.g., green spaces, rooftops, and rail yards), and avoidance of agricultural fields suggests Canada Geese may be minimizing risk rather than maximizing energy intake by using urban areas during winter. Future research should focus on the thermoregulatory and movement strategies employed by geese to survive in urban areas where food resources may be limited. Further, researchers interested in discouraging geese should evaluate their response to harassment when temperatures are below the lower critical temperature.

Migration is a physiologically demanding activity. Recent studies suggest that migrating birds can improve their immune and antioxidant status during stopover, implying that variation in stopover habitat can affect migrants' health. We studied 2 species that are strongly frugivorous during fall migration, Swainson's Thrushes (Catharus ustulatus) and Gray Catbirds (Dumetella carolinensis). We asked whether birds that used shrubland dominated by exotic plants experienced differences in mass change, immune function, and antioxidant status relative to conspecifics in native-dominated shrubland during fall stopover in Michigan, USA, in 2012–2013. We found no habitat-related differences in any of the measured health parameters for Swainson's Thrushes. However, Gray Catbirds using native-dominated shrubland retained mass while those in exotic-dominated shrubland lost mass in 2013. Gray Catbirds in exotic-dominated habitat that year also had poorer immune status (elevated granulocyte:lymphocyte ratio and reduced hemagglutination and haptoglobin) and had lower plasma total carotenoids (immunostimulatory antioxidants) relative to conspecifics in native-dominated shrubland. While these findings were not replicated in 2012, circulating antioxidant capacity was lower in both years in Gray Catbirds captured in exotic habitat. Habitat-specific estimates of dietary energy, carotenoid, and antioxidant content per unit mass of fruit were similar between habitat types for Swainson's Thrushes. For Gray Catbirds, however, the fruit diet was lower in carotenoids and antioxidant capacity, but not in energy, in exotic habitat. Our results provide evidence that differential use of stopover habitats may affect the immune and antioxidant status of migrating landbirds. Furthermore, our results suggest that habitat may affect health status based on the complex relationships among quality and abundance of food, food preferences, and refueling performance, which vary among species. We suggest that future studies measure immune and antioxidant metrics in addition to refueling performance to better understand the effects of stopover habitat use on landbird migrant health. This information may improve assessment of habitat quality for migrants.

Estimates of population abundance are important to wildlife management and conservation. However, it can be difficult to characterize the numbers of broadly distributed, low-density, and elusive bird species. Although Golden Eagles (Aquila chrysaetos) are rare, difficult to detect, and broadly distributed, they are concentrated during their autumn migration at monitoring sites in eastern North America. We used hawk-count data collected by citizen scientists in a virtual mark–recapture modeling analysis to estimate the numbers of Golden Eagles that migrate in autumn along Kittatinny Ridge, an Important Bird Area in Pennsylvania, USA. In order to evaluate the sensitivity of our abundance estimates to variation in eagle capture histories, we applied candidate models to 8 different sets of capture histories, constructed with or without age-class information and using known mean flight speeds ± 1, 2, 4, or 6 SE for eagles to travel between hawk-count sites. Although some abundance estimates were produced by models that poorly fitted the data (ĉ > 3.0), 2 sets of population estimates were produced by acceptably performing models (ĉ ≤ 3.0). Application of these models to count data from November, 2002–2011, suggested a mean population abundance of 1,354 ± 117 SE (range: 873–1,938). We found that Golden Eagles left the ridgeline at different rates and in different places along the route, and that typically <50% of individuals were detected at the hawk-count sites. Our study demonstrates a useful technique for estimating population abundance that may be applicable to other migrant species that are repeatedly detected at multiple monitoring sites along a topographic diversion or leading line.

The Canada Warbler (Cardellina canadensis) is a threatened species in Canada due to an annual decline of ∼3% over the last 50 yr. Some studies suggest that Canada Warblers prefer old-growth forest and that forestry practices may reduce suitable habitat, while other research indicates that the species will also use harvested areas. Differences in scale between habitat use studies and behavioral phenomena such as conspecific attraction may explain this discrepancy. We examined how Canada Warblers responded to forestry and conspecifics in Alberta, Canada. We used point counts, burst sampling, and behavioral observations to determine how the density, home range placement (second-order habitat use), within-home-range space use (third-order habitat use), and probability of pairing and fledging young of male Canada Warblers were influenced by postharvest conditions (i.e. amount, age [≤ 30 yr postharvest], and retention of unharvested fragments) and conspecifics. Male density was 86% lower in postharvest than in unharvested stands. However, males were 16.6 times more likely to place their home ranges in postharvest stands within 100 m of unharvested stands than 300 m into harvested areas, and 3 times more likely to place their home ranges 100 m from conspecifics than 300 m away. Within-home-range space use was 1.1 times higher 50 m from conspecifics than 350 m away, and 2.6 times higher 300 m from an edge than 100 m away. Use of harvested areas did not affect reproductive activity, but the probability of pairing was 1.8 times higher for males in low-density (2 males per 17.3 ha) than in high-density areas (7 males per 17.3 ha). Our results suggest that Canada Warbler use of postharvest stands on the boreal breeding grounds is more heavily influenced by conspecifics than by postharvest conditions. Because Canada Warbler territories are clustered, conservation efforts should prioritize the retention of large tracts of unharvested forest near occupied breeding sites.

A recent paper published in The Condor: Ornithological Applications by Raybuck et al. (2017) described the results of an analysis of potential effects of light-level geolocators on reproductive parameters and apparent annual survival of Cerulean Warblers (Setophaga cerulea). In a comparison of geolocator-tagged birds and color-banded control birds, the authors reported no discernible differences in several standard reproductive parameters, but a significant difference in apparent annual survival. Here, we show that the reported overall geolocator effect on annual survival may have obfuscated a large effect in one year, when one geolocator model and harness method were used, compared with no effect on annual survival in the second year of their study, when a different geolocator model and harness method were used. These more nuanced results suggest that Raybuck and colleagues may have identified variation in effects between geolocator marking methods for Cerulean Warblers, rather than a general geolocator effect on annual survival.

Our recent manuscript investigated geolocator-tagging effects on a small migratory warbler. Streby and Kramer (2017) suggest that a year effect may have been masked by our unequal sample sizes between years. They also argue that the difference in return rate between our geolocator-tagged and control birds was likely due to differences in harness styles used between years. We agree with their comment regarding the possibility that a year effect could have been masked by our unequal sample sizes. However, it is not possible to draw reliable conclusions from our data as to why we observed a reduced return rate for geolocator-tagged birds compared with color-banded controls, and attempts to do so are mere speculation. We also point out that both harness styles used in our study have been employed by a number of researchers who observed no reduced return rates for geolocator-tagged birds, including other species of parulid warbler. Researchers desiring to illuminate potential harness style effects on return rates should use large sample sizes of each harness type, in the same year, and search for all geolocator-tagged and control birds with equal effort.

Survival and recruitment estimates are important for predicting population viability and the efficacy of translocations. This information requires intensive monitoring postrelease, which is often economically or logistically infeasible. Since 2009, juveniles of the critically endangered Ridgway's Hawk (Buteo ridgwayi) have been translocated from Los Haitises National Park to Punta Cana, Dominican Republic. Here, we use multistate capture–recapture models to estimate survival and recruitment of translocated Ridgway's Hawks. We further examine whether survival or recruitment differed between sexes or translocation status (translocated vs. wild-reared birds in Los Haitises). Survival was relatively high for breeders, nonbreeders, and juveniles, and did not differ by translocation status or sex. Translocated juveniles were recruited into the breeding population at Punta Cana at more than double the rate of wild-reared juveniles in Los Haitises—likely because more unoccupied territories were available in Punta Cana. Our results show that translocation does not reduce survival, but does increase recruitment, of Ridgway's Hawks when territories are available in suitable habitat. Future work should evaluate the reproductive performance of Ridgway's Hawks in Punta Cana and determine the effects of translocations on the population in Los Haitises. Although the types of data collected during postrelease monitoring are often determined by funding, feasibility, and research objectives, our results demonstrate the importance of continued monitoring of translocated animals.