Journal of Field Ornithology最新文献

Studies of geographic variation in bird song can provide important insights into vocal evolution. An intraspecific approach, focused on a single species with a broad distribution, can be particularly helpful in understanding the diverse selective pressures on the characteristics of songs and singing behavior. Grass Wrens (Cistothorus platensis) are one such species, inhabiting tropical and temperate grasslands across the Neotropics. We studied Grass Wrens in Mendoza, Argentina, to determine the structure, organization, and delivery of their songs, song repertoire sizes, and patterns of song sharing among males in a resident, mainland south-temperate population. Over two breeding seasons, we recorded and analyzed 27,795 songs from 29 color-banded males. Songs of male Grass Wrens contained a few, low-volume introductory notes typically followed by one, but sometimes more, syllable types repeated as a trill. Males often repeated a sequence of two or three different song types (A-B-C, A-B-C, …) several times before switching to a different sequence (D-E-F). Syllable and song type sharing was high among males. The size of recorded syllable and song type repertoires of individual males varied with sampling effort. The introduction of new syllable or song types by males slowed, but did not reach asymptotes, with increasingly large samples of recordings. Many of these patterns are consistent with previous reports for Grass Wrens and other Cistothorus wrens, possibly representing core features of song design in this species group. Our results concerning song sharing among males in a resident population are also consistent with a previous proposed relationship between male song sharing and breeding-site fidelity. In the latter respect, Grass Wrens of Central and South America are more similar to Marsh Wrens than Sedge Wrens of North America, providing support for a recently proposed split between Grass Wrens and Sedge Wrens formerly considered conspecific.

Researchers should consider the costs and benefits of using tracking devices and choose devices that will optimize information gained with minimal effects on study organisms. With numerous technological advancements and devices marketed for avian research, selecting an optimal device and data collection interval (i.e., duty cycle) can be difficult. We evaluated six tracking-device types from two manufacturers (Pinpoint 10 [1-g; Lotek], Pinpoint Argos 75 [4-g; Lotek], Pinpoint Argos Solar S [6-g; Lotek], Ornitrack-10 [10-g; Ornitela], Ornitrack-15 [15-g; Ornitela], and Ornitrack-N35 [35-g; Ornitela]) and varied duty cycles to quantify (1) fix success rate for all units, (2) precision of location information for all units, and (3) battery voltage given the effects of duty cycle and reduced light for solar-rechargeable units (Ornitrack-10, Ornitrack-15, and Ornitrack-N35). Fix success rates for Pinpoint 10, Pinpoint Argos 75, Ornitrack-10, Ornitrack-15, and Ornitrack-N35 units were overall > 0.95. However, the Pinpoint Argos Solar S units had a lower fix success rate that varied with duty cycle intensity. The Pinpoint Argos 75, Pinpoint Argos Solar S, and Ornitrack-10 units were more precise (≥ 99% points were collected within 20 m of each other) than the Pinpoint 10, Ornitrack-15, and Ornitrack-N35 units (> 80% of points collected within 20 m of each other). For all devices, batteries maintained a high charge (i.e., battery charge lost during the dark hours was recovered or mostly recovered during the day) under high and intermediate light levels, and low and intermediate duty cycles. Light explained more variation in battery voltage than duty cycle. We encourage investigators to evaluate devices prior to deployment on birds to maximize data quality relative to their research questions.

For species with declining populations across their range, such as Lewis’s Woodpeckers (Melanerpes lewis), understanding habitat selection and its influence on reproductive outcomes are critical for effective management, especially in human-modified landscapes. We identified factors associated with habitat selection by Lewis’s Woodpeckers in the floodplain and burned forests across the Bitterroot Valley in Montana. We estimated population densities, determined reproductive outcomes, and examined the possible influence of forest characteristics on nest-site selection. Mean adult population densities of Lewis’s Woodpeckers were over three times greater in floodplain forest than burned forest (13.2 adults/km² vs. 4.1 adults/km², respectively). However, nest success was lower in floodplain (73%; CI = 62%, 82%) than in burned forest (88%; CI = 78%, 94%). Nest success also declined across the breeding season. Lewis’s Woodpeckers in the floodplain forest were more likely to nest in cavities in taller trees, forested areas with reduced canopy cover, and stands with more trees. In burned forests, the height of nest trees was the only distinguishing feature of nest-site selection. However, the characteristics of nest sites used by Lewis’s Woodpeckers did not predict nest success. Ultimately, nest success was high in both forest types and both play an important role in maintaining populations of Lewis’s Woodpeckers in our study system. Management strategies to conserve habitat for Lewis’s Woodpeckers in western Montana should focus on retention of trees and snags > 18 m in height in both forest types, as well as enhancing recruitment of cottonwoods in a floodplain forest.