D. Brent Burt

FORM, FUNCTION, AND FITNESS: PATHWAYS TO SURVIVAL

Abstract Two hypotheses have been considered in the literature regarding how anuran morphology reduces predation risk: by (1) improving escape swimming performance, or (2) using the tail as a lure to draw predator strikes away from the body of the tadpole. We investigated these hypotheses using a modification of the morphology, performance, and fitness path analysis of Arnold (1983, Am. Zool. 23:347–361). Indirect effects of morphology on fitness, as mediated by burst swimming speed, as well as direct paths from morphology to survival with dragonfly larvae were included in the path model. Tadpole morphology did affect burst swimming speed, however, burst swimming speed did not influence survival. Fast tadpoles were larger overall, had long tails, deep tail muscles, and proportionally small bodies. In addition, a shape trait similar to published descriptions of the tail lure morphology had a direct relationship with survival. Thus, only the tail lure effect was supported. This study documents the utility of analyzing multiple trait effects and demonstrates that including direct paths between traits and fitness in the morphology, performance, and fitness path model allows evaluation of alternative hypothesis of selection.

Colony site choice of blue-tailed bee-eaters: influences of soil, vegetation, and water quality

All bee‐eaters (Family Meropidae) are cavity nesters, excavating terrestrial burrows in sites ranging from flat ground, to small mounds of soil, steep earthen banks seen in road clearings, eroded cliff faces, and river gorges. However, very little is known concerning the environmental factors that influence nest site selection in bee‐eaters. We addressed abiotic and biotic issues associated with colony site choice in blue‐tailed bee‐eaters (Merops philippinus) nesting on Kinmen Island, off mainland China, from 2000 to 2002. About 89% of the colonies were located on slopes with soils of sandy loam and the other 11% on sandy clay loam. No colony was found on clay loam, which covered 20% of the island. The sandy loam and sandy clay loam had lower soil pressure, density and moisture, which, presumably, were easier for bee‐eaters to excavate and provided better drainage and ventilation for nest cavities. Bee‐eaters avoided placing nest cavities in areas with dense vegetation and abandoned colony sites when they became overgrown. Vegetation would impede excavation and decrease the detectability of predators. Bee‐eaters may prefer colony sites near water bodies showing water chemistries indicative of more biological productivity, especially in relation to the diversity and abundance of their major prey, dragonflies.

Group size and nest success in Red-cockaded Woodpeckers in the West Gulf Coastal Plain: helpers make a difference

Abstract We studied the relationships between Red-cockaded Woodpecker (Picoides borealis) group size and nest productivity. Red-cockaded Woodpecker group size was positively correlated with fledging success. Although the relationships between woodpecker group size and nest productivity measures were not statistically significant, a pattern of increasing clutch size and number of hatchlings with increasing group size was apparent. The presence of helpers appeared to enhance the survival of nestlings between hatching and fledging. The contribution that helpers make to nestling feeding and incubation, cavity excavation, and territory defense appears to have a positive effect on nest productivity. A threshold number of helpers may be necessary before a significant benefit for fledging success is realized. Nests with four and five group members fledged more young than nests with two or three group members. Whether partial brood loss occurred or not within a nest was primarily a function of clutch size and the number of hatchlings. Although partial brood loss did affect the number of young fledged from individual nests by removing young from nests with high numbers of hatchlings, woodpecker group size appeared to be the primary determinant of fledging success.

SOCIAL AND BREEDING BIOLOGY OF BEE-EATERS IN THAILAND

Abstract I report on the social and breeding biology of four bee-eater species in Thailand. Little Green Bee-eaters (Merops orientalis) breed cooperatively in clusters of overlapping territories. Cooperative breeding units have one to two helpers that join the breeding pair only after incubation has begun. Nests rarely are left unguarded due to threats of predation and possible intraspecific brood parasitism. Males also guard their mates against extrapair copulations. The Blue-tailed Bee-eater (M. philippinus) breeds cooperatively and has a complex social system, with evidence suggestive of intraspecific brood parasitism and extrapair copulation. I provide evidence that the Bay-headed Bee-eater (M. leschenaulti) breeds cooperatively and report observations of noncooperative breeding at one nest in the Blue-bearded Bee-eater (Nyctyornis athertoni).

Relationships Between Habitat and Snag Characteristics and the Reproductive Success of the Brown-headed Nuthatch (Sitta pusilla) in Eastern Texas

Abstract Habitat use and reproductive success of the Brown-headed Nuthatch (Sitta pusilla Latham) were studied in East Texas during the 2001–2002 breeding seasons. We compared nest cavity selection at used and randomly selected non-used areas. Height of nest trees, midstory density, and percent leaf litter were negatively correlated with nest site selection. Brown-headed Nuthatches showed a strong preference for short snags; yet placed their nest cavity entrances near the top of the snags. While nuthatches may be selecting for habitats with little or no midstory density, percent of leaf litter in the nest sites is most likely the consequence of frequent burning. No significant differences among habitat variables and snag characteristics were found between successful and failed nest cavities. Additionally, no habitat variables were correlated with the number of chicks fledged per nest. Predation was the major cause of nest failure in this study.

Habitat Use and Avoidance by Foraging Red-Cockaded Woodpeckers in East Texas

Abstract Picoides borealis (Red-cockaded Woodpecker) is an endangered bird endemic to the Pinus (pine) ecosystems of the southeastern US. Mature pine savannahs with a minimal midstory and lush herbaceous groundcover represent high-quality habitat. This study examines the foraging-habitat patterns of Red-cockaded Woodpeckers in East Texas. We present a logistic regression model that best differentiates between foraged and non-foraged habitat. Increases in hardwood-midstory basal area have the greatest negative impact on the probability of Red-cockaded Woodpeckers selecting a habitat patch for foraging. Five additional variables negatively impact foraging probability: shrub height, diameter at breast height (DBH) of pine midstory, canopy closure, density of pine midstory, and density of hardwood midstory. Our model shows a high degree of accuracy as to the probability of habitat-patch selection for Red-cockaded Woodpeckers foraging in East Texas forests composed of different pine species.

Vegetative Characteristics of Bachman's Sparrow Habitat in the West Gulf Coastal Plain

Abstract While Peucaea aestivalis (Bachmans Sparrow) will use several habitat types (e.g., pine savanna, pine plantations, clear cuts, abandoned fields), specific vegetative conditions must be present for a site to be acceptable. Bachmans Sparrow presence/absence was examined in forested (mature Pinus palustris [Longleaf Pine] forest and mid-aged pine plantations) and early successional habitats (clear cuts and three-year-old pine plantations) to determine which vegetation variables were best for predicting sparrow occurrence. Across all sampled habitats, the probability of Bachmans Sparrow presence increased with increases in canopy cover and percent grass groundcover. Probability of presence decreased with increases in shrub-layer rating and percent bare ground. When considering only forested habitats, the probability of Bachmans Sparrow presence increased with increasing canopy cover and percent grass groundcover, but decreased with increasing canopy height, shrub height, and stand basal area. In early successional habitats, the probability of Bachmans Sparrow presence increased with greater grass groundcover and decreased with more bare ground. Also, there were more occupied sites in forested habitats than in early successional habitats.

Rainfall, El Niño, and Reproduction of Red-cockaded Woodpeckers

Abstract This study examines the relationship between Red-cockaded Woodpecker (Picoides borealis Vieillot) reproduction and rainfall during May when group members are provisioning nestlings with food. Patterns of variation over a 4-year period of approximately 30 woodpecker groups suggested that the mean number of hatchling deaths was positively related to the amount of rainfall that occurred during May. During the same 4 years, the mean number of young fledged from nests appeared to be inversely related to May rainfall. Observations of nestling provisioning behavior during four breeding seasons indicate that group members slow down or stop feeding nestlings during periods of heavy rainfall. During a 20-year period, total May rainfall was related to the percentage of woodpecker groups producing fledgling-sized young in cavities (rs = −0.56, P = 0.0097) and the occurrence of El Niño events (rs = −0.50, P = 0.0347).