Journal of Field Ornithology最新文献

The Kohala volcano is home to the most spatially isolated population of Hawaiian forest birds on Hawai‘i Island and contains one of the few native bird populations in the state that has not been monitored since the original Hawai‘i Forest Bird Survey (HFBS) in 1979. We surveyed 143 stations across 13 transects in Pu‘u ‘O ‘Umi Natural Area Reserve on Kohala from February through April 2017 and compared our results to data from the 1979 HFBS conducted at 80 stations across three transects in the same location as our study site. We detected 2806 individuals of 15 species and measured relative abundance, relative occurrence, and density for seven species. We observed changes in species densities ranging from −8.4% (Hawai‘i ‘Elepaio, Chasiempis sandwichensis) to +714% (‘I‘iwi, Drepanis coccinea). Equivalence testing showed meaningful increases in population densities for all but one species, the Hawai‘i ‘Elepaio. The increases in population densities on Kohala are in stark contrast to the widespread declines in population densities of native species elsewhere in Hawai‘i. Relative occurrence was greater in 2017 than in 1979 for all species except Hawai‘i ‘Elepaios and House Finches (Haemorhous mexicanus), and relative abundance increased for all species except Hawai‘i ‘Elepaios, House Finches, and Melodious Laughing Thrushes (Garrulax canorus). We also documented the range expansion of Japanese Bush Warblers (Cettia diphone) in Kohala. Our results indicate that this spatially isolated avian community remains biologically diverse, and most population densities are increasing in the study area. Our results provide a framework for future surveys and a baseline for understanding possible changes in population and community dynamics as birds respond to climate change and avian disease on Kohala volcano.

For signal divergence to drive speciation, receivers should perceive structural differences in divergent signals; similar-structured signals from closer relatives are expected to elicit stronger responses than dissimilar signals from distant relatives. Two mechanisms can affect receiver responses to passerine song: (1) sympatric song familiarity and (2) an innate auditory template used to assess acoustic similarity. We examined the role of acoustic similarity by comparing behavioral responses of male Bermuda White-eyed Vireos (Vireo griseus bermudianus) to playback of the songs of allopatric species from across the family Vireonidae. Phylogenetic distance between the focal and stimulus species predicted response strength. Males uttered fewer vocalizations, had fewer speaker flyovers, and remained farther from the speaker during playback of the songs of more distantly related vireos. We then tested whether structural similarity of playback songs, as defined by three phylogenetically conserved song traits, explained these relationships. As predicted, males uttered fewer vocalizations, had fewer speaker flyovers, and remained farther from the speaker in response to more dissimilar songs. Collectively, our results suggest that male Bermuda Vireos perceive and respond to interspecies variation in the phylogenetically conserved song traits of allopatric species of vireos. This suggests that song divergence, and the ability to distinguish divergent songs, reinforces reproductive isolation and competitor exclusion.

The study of avian nesting biology in North America and Europe has a long history, resulting in an expansive and information-rich literature. In contrast, the tropics have been relatively neglected and, in most ways, we are still at the frontier of exploration. Data about basic nest descriptions and natural history information are still lacking for many Neotropical species; standardization of data collection methods is needed for comparative analyses. Hence, our goals are: (1) motivate a new generation of Neotropical naturalists to collect nesting data by providing basic tips on how to find nests and collect basic data, (2) provide guidelines on how to use and analyze basic data, (3) highlight the importance of collections, (4) describe modern monitoring techniques, and (5) suggest how these data can be used to fill important gaps concerning the breeding biology of tropical birds. Understanding avian nesting biology and the biotic and abiotic factors that influence nesting success is crucial for a better understanding of bird population dynamics and breeding strategies at the community level, and can form the basis for the development of sound conservation measures.

The value of saline lakes and associated wetlands as habitats in the xeric Great Basin is dependent on having water of sufficient quantity and quality to support wetland-dependent birds. To inform conservation and management of these habitats, models are needed to link birds and hydrological changes due to climate and human water use. We modeled seasonal relationships between counts for 35 migratory shorebird, waterfowl, and other waterbird species or taxonomic groups and hydrological metrics at Bear River Bay, a globally Important Bird Area at Utah’s Great Salt Lake. We found that increased fall surface flows to the bay increased counts of 13 species, including American Avocets (Recurvirostra americana), American White Pelicans (Pelecanus erythrorhynchos), American Wigeons (Mareca americana), Northern Pintail (Anas acuta), Redheads (Aythya americana), and Ruddy Ducks (Oxyura jamaicensis). Increased spring surface flows increased counts of Forster’s Terns (Sterna forsteri) and the sandpiper group, whereas intermediate spring flows produced peak counts for American White Pelicans. Thus, conservation or management actions that increase seasonal flows to Bear River Bay are expected to increase bay use by diverse members of the avian community. Counts for 11 species or taxonomic groups responded positively or negatively to the seasonal elevation of Great Salt Lake, and these responses are hypothesized to reflect the relative availability of habitats within the bay versus the lake as a whole. Our models provide tools that allow managers to understand how hydrological changes associated with climate change and human water use will affect birds in Bear River Bay. Addressing lake-wide and regional population implications of changing hydrological conditions at Bear River Bay, Great Salt Lake, and other locations across the Great Basin will require a regionally coordinated assessment of hydrology, habitat, and bird movements in response to changing habitat conditions.

Recently fledged birds often experience low survival as they undergo rapid changes in their behavior, (e.g., habitat use, mobility, and foraging rate). For species of conservation concern, information about the post-fledging period can be critical for effective management and conservation. We investigated the post-fledging ecology of endangered Golden-cheeked Warblers (Setophaga chrysoparia) in central Texas. Current management guidelines focus on nesting habitat even though songbird fledglings may use entirely different habitats. We radio-tracked fledglings (N = 23) to assess their habitat use, estimate daily survival, and observe age-based behavioral changes. Habitat used by fledglings was similar to adult nesting habitat and was dominated by Ashe juniper (Juniperus asheii; 75%) and oak (Quercus spp.; 21%). Apparent fledgling survival was 65%, and the estimated daily survival rate of fledglings during their first 4 weeks post-fledging was 0.985 (95% CI = 0.971–0.993). To investigate the factors associated with predation, we estimated survival while excluding mortality events due to exposure. Estimated survival was greater in areas with more junipers than oaks. As fledglings aged, use of oaks as foraging substrates increased as did their prey capture rates (nearly twice as many prey captured per hour in oaks than in junipers). Current management recommendations for nesting adult Golden-cheeked Warblers specify maintaining mature juniper–oak forests composed of ~70% juniper, a recommendation that also appears to accommodate fledglings. Fledgling Golden-cheeked Warblers acquire unique benefits from junipers (i.e., safety) and oaks (i.e., foraging opportunities), so management plans should include the maintenance of both junipers and oaks.

Group living is a widespread social strategy that allows animals to optimize foraging with dynamic trade-offs between reduced predation risk, enhanced foraging, and increased competition. Birds across terrestrial habitats form mixed-species flocks, where dozens of resident and migratory species forage together throughout the day. The effect of flock participation and group size on the foraging behavior of migratory and resident species is poorly known, particularly in the tropics. Using foraging observations, we examined the effects of flock participation on the foraging ecology of four species of Neotropical migrants and three resident species in shade-grown coffee plantations in the Colombian Andes in 2011. We showed that resident and migrant birds in mixed-species flocks largely increased the number of foraging attempts, expanded their foraging repertoire, and exhibited greater overlap in use of foraging maneuvers compared with solitary individuals. We found an effect of group size on foraging rate, with feeding attempts increasing monotonically or showing a hump-shaped pattern, and also found that movement rates increased with increasing flock diversity. These results support the idea that flock participation enhances foraging success and reduces perceived predation risk, but also show niche convergence among flocking species, along with higher movement rates and more agonistic interactions as group size increases. Finally, our results provide insight into the importance of mixed-species flocks for birds of conservation concern, including Cerulean Warblers (Setophaga cerulea), a Neotropical migrant shown to be highly restricted to foraging in flocks in their wintering areas.

Accurate estimation of populations of secretive marsh birds is difficult, especially during the non-breeding season when vocalizations are infrequent. Thus, dynamics of marsh bird populations remain relatively unknown, especially during the non-breeding season along the northern coast of the Gulf of Mexico. To address this lack of information about populations of marsh birds during the non-breeding season along the coast of Mississippi, we conducted 650 surveys along 130 line transects distributed across a spatially balanced sampling framework of tidal marshes from December to February 2018–2020. Using hierarchical distance-sampling models for unmarked populations, we estimated species-specific non-breeding population densities, abundances, and vegetation associations of eight species of marsh birds across a mosaic of tidal marsh communities, spanning oligohaline to polyhaline emergent and open marsh systems. We estimated that 127,000 Red-winged Blackbirds (Agelaius phoeniceus), 106,000 Marsh Wrens (Cistothorus palustris), 37,000 Seaside Sparrows (Ammospiza maritima), 17,000 Clapper Rails (Rallus crepitans), 15,000 Swamp Sparrows (Melospiza georgiana), 14,000 Nelson's Sparrows (Ammospiza nelsoni), 10,000 Sedge Wrens (Cistothorus platensis), and 2000 Common Yellowthroats (Geothlypis trichas) overwintered in the tidal marshes of Mississippi during our study. Further, we show that these species associate with different salinity ranges and vegetation communities within the broader estuarine marsh. Our population estimates and vegetation associations for vulnerable species provide important baselines from which assessments of future change can be compared.

Cassia Crossbills (Loxia sinesciuris) are endemic to two small mountain ranges in southern Idaho, the South Hills and Albion Mountains. Although previous studies have shown the importance of mature Rocky Mountain lodgepole pines (Pinus contorta latifolia) that have accumulated a large canopy cone bank as a food resource for Cassia Crossbills, information about nest-site selection is lacking. We located 49 Cassia Crossbill nests in the South Hills in 2001–2002, characterized their locations and surrounding habitat, and characterized the habitat in 26 nearby random locations for comparison. We also include information on tree species and height for 57 nests located from 2003 to 2006. Cassia Crossbills built nests where foliage was most extensive in the upper canopy of large lodgepole pines in relatively dense and mature stands dominated by lodgepole pine. Nests were usually on lateral branches on the south side of trees, but the slope and aspect of nest locations were not distinctive. Other species of crossbills generally build nests in dense foliage, but, unlike Cassia Crossbills, they usually nest in relatively open stands, presumably to reduce the risk of nest predation by tree squirrels. Because tree squirrels do not co-occur with Cassia Crossbills, their preference to nest in dense forests may reduce exposure to wind and inclement weather and reduce the likelihood of detection by nest predators such as Common Ravens (Corvus corax). We believe that nest sites will not be limiting if there is an adequate seed supply. However, this requires a large canopy cone bank throughout the range of Cassia Crossbills, an outcome that is uncertain in the face of increasing temperatures and increasing fire frequency and intensity.

Globally, billions of U.S. dollars are spent annually to provide food for wild birds. The variety of foods offered continues to diversify, yet the consequences for wildlife of this widespread human activity are relatively unexplored, as are the relative benefits of different types of supplemental food. To investigate the potential implications of supplemental feeding for reproductive success, we experimentally examined the effects of providing supplemental insect prey on nestling mass for two species of birds across two nesting seasons (2016–2017) in Tompkins County, New York. Nesting adults in the experimental group were provided with 10 grams of insect larvae (mealworms, Tenebrio molitor) per day from the day eggs hatched until nestlings fledged. Results were mixed, with nestling Eastern Bluebirds (Sialia sialis) having 5.2% greater mass at fledging in supplemented nests, on average, than those in nests not receiving supplemental food. In contrast, no difference in mass was detected between treatment and control groups of nestling Black-capped Chickadees (Poecile atricapillus). Models also supported variation in bluebird mass depending on weather conditions, with greater mass at higher mean temperatures and during periods with less precipitation. Although people who feed wild birds are often motivated by a desire to contribute to conservation and help birds, the consequences of supplementing birds vary, and feeding may not have the desired effects across taxa. People seeking to improve the condition of nestlings should not assume that feeding is universally beneficial and should also consider making habitat improvements, keeping cats indoors, and limiting access of predators to nest boxes by installing predator guards. Implementing a suite of conservation behaviors may be more effective at promoting reproductive success than feeding alone.