Michael P. Ward

Nearctic Neotropical migratory songbirds incur the highest mortality during migration. En-route, songbirds rely on a network of stopover sites to rest, refuel, and/or seek refuge during poor weather. Conservation strategies prioritize protection of sites that best meet these needs. However, the specific function of a stopover site is expected to vary in relation to factors, such as geographic location, surrounding landscape, and weather. To identify sites with the highest conservation value for migratory songbirds, a conceptual framework was independently developed to classify sites into three functional categories based on their geographic and landscape features: fire escapes, convenience stores, and full-service hotels. The few attempts to empirically validate this framework have focused on temperate stopover sites. We evaluated the framework by testing the hypothesis that a site’s geographic and landscape characteristics can predict its function. We used capture and radio-tracking data at an island and mainland site in the Yucatan Peninsula, Mexico to quantify mean and variance in daily capture rate, body condition, stopover duration, and departure behavior during autumn, with a focus on four species: Swainson’s Thrush (Catharus ustulatus), Red-eyed Vireo (Vireo olivaceus), Gray Catbird (Dumetella carolinensis), and Prothonotary Warbler (Protonotaria citrea). Our results supported our predictions that the island functions as a fire escape, providing refuge for very high numbers of birds after encountering crosswinds or headwinds over the Gulf of Mexico, and the mainland forest site serves as a full-service hotel. The framework provides valuable insight for strategic conservation planning and management of stopover sites for songbirds. We suggest future studies evaluate the framework’s application to non-forest bird species. Additionally, we encourage collaborative efforts to consolidate and integrate tracking data, capture data from migration banding stations, and radar-based bird density estimates across a broad geography to test the framework’s ability to inform conservation planning across species’ full migratory range.

Migratory bird populations can be limited by events in disparate parts of the world. Birds wintering in tropical regions are facing rapid habitat loss, climate change, and intensive agricultural regimes, potentially contributing to population declines. However, an understanding of basic nonbreeding ecology of species, such as habitat and space use, is critical for determining if this is the case. Populations of the nocturnal/crepuscular Eastern Whip-poor-will (Antrostomus vociferus) have declined by 70% since the 1960’s, yet data on the species are sparse outside of the breeding season. We extracted data from 41 archival GPS tags deployed on whip-poor-wills and estimated nonbreeding home ranges and land covers used. We used satellite imagery and stable carbon and nitrogen isotope values from claws grown during the nonbreeding season to analyze how land cover and habitat moisture impacted home range size and relative trophic level. Forest was by far the most prevalent land cover used by whip-poor-wills, occurring in all home ranges and accounting for >80% of diurnal roosting points. We found that less forest, the presence of agriculture, and more edge (irrespective of land cover) were associated with larger home ranges. Stable isotope values differed by broadscale ecoregion but not local land cover characteristics in our study, indicating that regional idiosyncrasies or broadscale processes can be more important in determining stable isotope ratios. Our findings suggest that the loss, fragmentation, and replacement of forest by agriculture in the core of the whip-poor-will’s nonbreeding range may represent a threat to the species, as they rely heavily upon forest, and appear to alter space use in response to changes in forest cover.

Aim: A full annual cycle approach to conservation and understanding of regional population trends requires an understanding of migratory connectivity. We present tracking data on the eastern whip‐poor‐will (Antrostomus vociferus), a Neotropical migrant that has declined by 70% in recent decades. When and where populations of this species are limited throughout the annual cycle is poorly understood.Location: Breeding area: midwestern United States; passage area and winter area: midwestern/southern United States, Mexico, Central America.Methods: We utilized data from 52 archival GPS tags from five breeding areas covering a 9.5‐degree latitudinal span (~1000 km) of the whip‐poor‐will breeding range in the summers of 2017 and 2019. We identified migratory routes and spatiotemporal bottlenecks, stopover and wintering locations, calculated migratory connectivity throughout migration and on the wintering grounds and tested predictions for three latitudinal connectivity patterns.Results: Whip‐poor‐wills circumvented the Gulf of Mexico, and populations across a large latitudinal gradient came together in eastern Texas in early October, resulting in decreased connectivity throughout migration. Breeding‐winter migratory connectivity was low (MC = 0.22 ± 0.12), with extensive overlap of core wintering areas in southern Mexico and Guatemala. The overlap of wintering areas by individuals from dispersed breeding latitudes suggests that whip‐poor‐wills most closely resemble telescopic migrants.Main conclusions: Circumventing the Gulf of Mexico influenced connectivity in the whip‐poor‐will, funnelling individuals into a small region in eastern Texas in migration and likely influencing breeding‐winter connectivity. Thus, geographically dispersed breeding populations overlap in space and time during migration and winter, and non‐breeding season conditions affecting populations (both positively and negatively) impact individuals from across the core breeding range. For example, extensive deforestation occurring in the whip‐poor‐will's core wintering area likely impacts individuals from all five deployment locations. We demonstrate that combining multiple indices of spatiotemporal cohesion is critical to fully understand how migratory animals are distributed in the non‐breeding season.

Horsley, N. P., and M. P. Ward. 2021. Why is the Common Grackle becoming less common? Avian Conservation and Ecology 16(2):7. https://doi.org/10.5751/ACE-01879-160207

Scavenging is an important ecological function that increases individual fitness and transfers energy between trophic levels. Scavenging by owls has been documented opportunistically through direct observations, camera trapping, and pellet analyses, but it is unknown how frequent or widespread the behavior is. We documented three new scavenging events from North America and Europe, and also performed a systematic literature review of the reports documenting scavenging by owls. The number of such reports was similar in each decade from the 1970s to the 2000s, but the decade of the 2010s had more reports than all previous decades combined. Owls scavenged primarily on mammals (81%), followed by birds (16%) and reptiles (3%); almost half (47%) of carrion scavenged were Artiodactyla (hoofed mammals) and most of the species scavenged were larger than the feeding owl. Most reports documenting scavenging by owls were from either Europe (n=14) or North America (n=11), with few reports from Asia (n=2), South America (n =2), or Australia (n=1), and none from Africa. The most frequent type of report was direct observations (n= 14), followed by camera trapping (n=9) and pellet analyses (n=6). Our review indicates that scavenging is a widespread behavior among owl species, but most observations were opportunistic, suggesting that additional incidents of scavenging by owls are likely unobserved. Further research is needed to establish the frequency of scavenging by owls and the effects that scavenging may have on owl populations and scavenging communities.

A number of wildlife species have recovered from the brink of extinction to flourish and, in some cases, even become a commonly recognized urban species (e.g., Canada goose [Branta canadensis]). Broadly extirpated from much of their historical range in North America, the sandhill crane (Antigone canadensis) demonstrated this potential for population recovery. The trajectory of the eastern population of greater sandhill cranes is remarkable—perhaps as many as 90,000 cranes now occur throughout the same Great Lakes states that reported only dozens of birds less than a century ago. However, understanding future population growth of the species remains uncertain because breeding birds are increasingly exposed to the pressures of urban sprawl and a changing agricultural landscape. From 2009 to 2014 we investigated the survival of sandhill crane nests and young up to 11 weeks of age (the point at which they are capable of flight) in the core of the eastern population's range in central Wisconsin and at its peripheral extent in a rapidly developing urban region of northeastern Illinois, USA. We located crane nests via systematic surveys on foot and from helicopters, we then radio‐tagged the young and monitored them until they died or were capable to sustained flight. Overall, young were more likely to hatch from nests in Illinois (60%) than in central Wisconsin (46%), regardless of differences in land cover surrounding the nest site. In contrast, the survivorship of young was positively correlated with urban land cover in both regions but higher in central Wisconsin (54%) than in northeast Illinois (27%). Overall, the probability of producing young was greater in landscapes with more urban development, regardless of region. We suggest that differences in predator composition, predator behavior, and crane density between rural and urban areas is the primary reason for the difference in crane productivity. Higher recruitment of sandhill cranes using urban landscapes may allow cranes to echo the population trajectory of urban Canada geese. We anticipate that sandhill cranes will continue to use urban landscapes, and likely expand their geographic range as breeding pairs benefit from the increased survivorship of young in those landscapes. © The Wildlife Society, 2019

Many migratory bird species are declining, and the migratory period may limit populations because of the risk in traversing large geographical features during passage. Using automated radio-telemetry, we tracked 139 Swainson's thrushes (Catharus ustulatus) departing coastal Alabama, USA and crossing the Gulf of Mexico to arrive in the Yucatan Peninsula, Mexico during autumn. We estimated apparent survival and examined how extrinsic (weather variables and day of year) and intrinsic (fat load, sex and age) factors influenced survival using a mark-recapture approach. We also examined how favourability of winds for crossing the Gulf varied over the past 25 years. Fat load, day of year and wind profit were important factors in predicting which individuals survived crossing the Gulf. Survival estimates varied with wind profit and fat, but generally, fat birds departing on days with favourable wind profits had an apparent survival probability of greater than 0.90, while lean individuals with no or negative wind profits had less than 0.33. The proportion of favourable nights varied within and among years, but has increased over the last 25 years. While conservation strategies cannot improve extrinsic factors, they can provide opportunities for birds to refuel before crossing large geographical features through protecting and creating high-quality stopover sites.

Most species are distributed such that their density and occupancy is greatest in one habitat, although they are found in other habitats. For example, a species with a high affinity for forests (its primary habitat) may also use urban areas and shrublands (its alternative habitat), although occupancy of these habitats would be lower. While habitat loss is the main conservation threat for most species, less is known about how changes in primary and alternative habitats impact populations. We used a systematic bird survey of the state of Illinois that spanned the past century to investigate how use of specific habitats was related to population changes. Specifically, we used a hierarchical Bayesian model to investigate the relationship between changes in statewide occupancy (probability a species would occur in a study site) and use of specific habitats (probability a species would be in a specific habitat within our study sites) for 66 species sampled in 1906–1909 and 2006–2008. Changes in the use... RESUMEN La mayoría de las especies están distribuidas de tal modo que sus densidades y ocupaciones son mayores en un hábitat, aunque se las encuentra en otros hábitats. Por ejemplo, una especie con alta afinidad por los bosques (su hábitat primario) también puede usar áreas urbanas y arbustales (su hábitat alternativo), aunque la ocupación de estos hábitats fuera menor. Aunque la pérdida de hábitat es la principal amenaza de conservación para la mayoría de las especies, se sabe menos sobre cómo los cambios en hábitats primarios y alternativos impactan a las poblaciones. Usamos un censo sistemático de aves del estado de Illinois que abarcó el siglo pasado para investigar cómo el uso de hábitats específicos se relacionó con los cambios poblacionales. Específicamente, usamos un modelo bayesiano jerárquico para investigar la relación entre cambios de ocupación a escala de estado (probabilidad de que una especie estuviera presente en un sitio de estudio) y uso de hábitats específicos (probabilidad de que una e...

Amphibian populations are declining worldwide, with habitat loss and alteration being a primary driver of many declines. Management strategies to mitigate these declines include translocation and creation or restoration of breeding habitats, yet these techniques are not always effective. We examined whether conspecific attraction—a management tool frequently used in avian conservation—would be similarly valuable in management and conservation of anuran amphibians (i.e., frogs and toads). We broadcast conspecific chorus sounds at unoccupied, artificial breeding ponds for six anuran species across three field sites. We documented when frogs arrived at each pool and when eggs were laid. We compared differences in number of pools found with adults and egg masses between playback and control pools and examined latency to first colonization. We found that Mexican spadefoots colonized playback ponds faster and more often than control ponds, while Cope’s gray treefrogs, Arizona treefrogs, green frogs, spring peepers, and wood frogs exhibited weak or non-existent responses. We discuss why breeding ecology may influence tendency to exhibit conspecific attraction and how this behavior could be used in amphibian management and conservation.