Lifecycle exposure to perchlorate differentially alters morphology, biochemistry, and transcription as well as sperm motility in Silurana tropicalis frogs.

Perchlorate (ClO) contamination has been reported in ground and surface waters across North America. However, few studies have examined the effects of prolonged exposure to this thyroid hormone disrupting chemical, particularly at environmentally relevant concentrations in lower vertebrates, such as amphibians. The aim of this study was to examine the effects of a yearlong chronic exposure to ClO in adult male and female Western clawed frogs (Silurana tropicalis).

DELAYED PLUMAGE MATURATION IN PASSERINE BIRDS: RELIABLE SIGNALING BY SUBORDINATE MALES?

Three hypotheses (Cryptic, Female Mimicry, and Winter Adaptation) have been proposed to explain the occurrence of delayed plumage maturation (DPM) in passerine birds. We show that each of these hypotheses is really a composite of two different questions about: 1) the proximate function of dull plumage in second year (SY) males and 2) the selective mechanism that has favored that proximate function. We review the three hypotheses in the context of this distinction, and we find little evidence clearly supporting any of them.

What do foraging hummingbirds maximize?

Hainsworth and Wolf (1976) reported that under certain conditions hummingbirds made food choices which did not maximize their net rate of energy intake while foraging. They concluded that the birds were not foraging optimally. We show here that their birds probably maximized a different utility function, the net energy per unit volume consumed (NEVC), which appears to be an optimal choice on a time scale longer than that of a foraging bout.

Nectar extraction by hummingbirds: response to different floral characters.

Handling times of hummingbirds (Amazilia rutila and Cynanthus latirostris) visiting artificial flowers were a positive function of corolla length, nectar volume and nectar concentration. Corolla angle had no consistent effects on handling times. A multiple regression model explained 83% of the variation in handling times for these two species.

Energy limitation of hummingbird populations in tropical and temperate communities.

Regular censuses were conducted at both a temperate alpine and a tropical lowland site to determine seasonal changes in the composition of hummingbird communities and the availability of their food. From these data we calculated the total daily energy demand by the hummingbirds (Daily Energy Expenditure; DEE) and the daily energy supply available from floral nectar (Daily Energy Production; DEP) for each community census. Despite differences in habitat type and hummingbird community structure between these two sites, the hummingbird populations were often at or near carrying capacity.

A winter feeding experiment on an island Song Sparrow population.

Supplemental food, in the form of millet seed, was provided to half of an island Song Sparrow population during the 1978-1979 winter to test if winter food influenced: (1) overwinter survival; (2) winter wights; (3) breeding density in 1979 and (4) 1979 breeding performance.Territorial males were most dominant at feeders and may have restricted access of young to feeders. Young females were most subordinate at feeders.