Behavior of buff-breasted sandpipers (Tryngites subruficollis) during migratory stopover in agricultural fields.

BACKGROUND: Understanding the behavior of birds in agricultural habitats can be the first step in evaluating the conservation implications of birds' use of landscapes shaped by modern agriculture. The existence and magnitude of risk from agricultural practices and the quality of resources agricultural lands provide will be determined largely by how birds use these habitats. Buff-breasted Sandpipers (Tryngites subruficollis) are a species of conservation concern. During spring migration large numbers of Buff-breasted Sandpipers stopover in row crop fields in the Rainwater Basin region of Nebraska. We used behavioral observations as a first step in evaluating how Buff-breasted Sandpipers use crop fields during migratory stopover. METHODOLOGY/PRINCIPAL FINDINGS: We measured behavior during migratory stopover using scan and focal individual sampling to determine how birds were using crop fields. Foraging was the most frequent behavior observed, but the intensity of foraging changed over the course of the day with a distinct mid-day low point. Relative to other migrating shorebirds, Buff-breasted Sandpipers spent a significant proportion of their time in social interactions including courtship displays. CONCLUSIONS/SIGNIFICANCE: Our results show that the primary use of upland agricultural fields by migrating Buff-breasted Sandpipers is foraging while wetlands are used for maintenance and resting. The importance of foraging in row crop fields suggests that both the quality of food resources available in fields and the possible risks from dietary exposure to agricultural chemicals will be important to consider when developing conservation plans for Buff-breasted Sandpipers migrating through the Great Plains.

Bioenergetics-based modeling of individual PCB congeners in nestling tree swallows from two contaminated sites on the upper Hudson River, New York.

A bioenergetics-based model was used to simulate the accumulation of total PCBs and 20 PCB congeners by nestling tree swallows at two contaminated sites on the Upper Hudson River, New York. PCB concentrations in birds were calculated as the sum of inherited residues and those acquired through consumption of contaminated insects. Close agreement between simulations and measured residues in 5-, 10-, and 15-day-old nestlings was obtained when PCB concentrations in the diet were set equal to those in food boli taken from adult birds. These simulations were further optimized by fitting the value of a dietary assimilation efficiency constant. Fitted constants for both sites were similar and averaged about 0.7. An evaluation of model performance for individual congeners provided no evidence of metabolic biotransformation. The results of this study are consistent with a companion effort in which principal components analysis was used to compare PCB congener patterns in insects and in tree swallow eggs, nestlings, and adults. Together, these studies establish a quantitative linkage between nestling tree swallows and the insects that they consume and provide strong support for the use of nestling swallows as a biomonitoring species for exposure assessment.

Accumulation of PCB congeners in nestling tree swallows (Tachycineta bicolor) on the Hudson River, New York.

Tree swallows (Tachycineta bicolor) were used as a sentinel species to monitor the contamination and bioavailability of polychlorinated biphenyls (PCBs) in the Hudson River watershed. Several tree swallow nest box colonies around and downstream from Hudson Falls, NY, were studied. Tree swallow eggs, adults, and 5-, 10-, and 15-day-old nestlings were collected and analyzed for 103 PCB congeners. Emergent insects collected by net (primarily Odonata) or as a food bolus (primarily Diptera) taken from the mouths of adult tree swallows returning to the nest were analyzed in the same manner. Total PCB concentrations (wet weight) in eggs from two contaminated sites ranged from 9000 to 25,000 ng/g and accumulated to 32,000 and 96,000 ng/g in 15-day-old nestling at two contaminated sites. The congener patterns of PCBs in eggs, nestlings, and adults were compared to those found in emergent insects (Odonata and Diptera) using principal components analysis. The PCB patterns of the biota differed from that of Aroclor technical mixtures. PCB patterns in adult tree swallows were similar to those in eggs, while the patterns in dietary insects were similar to nestling tree swallows. Uptake rate constants were determined for tree swallow nestlings and compared between the two contaminated sites. The estimated PCB congener uptake rate constants were 0.008-0.02 d(-1) based on uptake in nestlings until day 15 post-hatch. The rate constants were comparable between the two study areas and may be used to predict nestling contamination at other locations. Our studies confirm the utility of nestling tree swallows to evaluate localized PCB contamination.

Cold temperature increases winter fruit removal rate of a bird-dispersed shrub.

We tested the hypothesis that winter removal rates of fruits of wax myrtle, Myrica cerifera, are higher in colder winters. Over a 9-year period, we monitored M. cerifera fruit crops in 13 0.1-ha study plots in South Carolina, U.S.A. Peak ripeness occurred in November, whereas peak removal occurred in the coldest months, December and January. Mean time to fruit removal within study plots was positively correlated with mean winter temperatures, thereby supporting our hypothesis. This result, combined with the generally low availability of winter arthropods, suggests that fruit abundance may play a role in determining winter survivorship and distribution of permanent resident and short-distance migrant birds. From the plant's perspective, it demonstrates inter-annual variation in the temporal component of seed dispersal, with possible consequences for post-dispersal seed and seedling ecology.

Resource availability, breeding site selection, and reproductive success of red-winged blackbirds.

Red-winged blackbirds are polygynous and show strong breeding site preferences, but it is unclear which environmental factors regulate their reproductive success and are ultimately responsible for shaping their patterns of habitat selection and their mating system. We evaluated the effect of variation in insect emergence rates on the reproductive success of male and female redwings nesting on replicate ponds. The number of male and female redwings that settled on a pond varied two- to three-fold among ponds, but was not related to insect emergence rates. Insect emergence rates had a positive effect on the number of nestlings successfully fledged by females, the number of nestlings fledged from male territories, and on the mass of nestlings at fledging. Typha stem density also varied widely among ponds, and was positively related to male and female settling density and mass of nestlings at fledging, but not to the number of nestlings fledged by females or males. We conclude that alternative breeding sites differ in their ability to support redwing reproduction, and that the availability of emerging odonates is an important environmental factor influencing the reproductive success of both male and female red-winged blackbirds.