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Perchlorate (ClO 4 - ) 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 4 - in adult male and female Western clawed frogs (Silurana tropicalis). Frogs were spawned and raised from fertilized embryo until sexual maturity in potassium perchlorate (KClO 4 )-treated water at different concentrations (0, 20, 53, and 107 μg/L). Developmental and reproductive indices - including adult morphology, androgen plasma levels, gonadal thyroid hormone- and sex steroid-related transcript levels, and sperm motility - were evaluated in male and female adult frogs. Female growth (e.g., body mass, snout-vent length, and hind limb length) was significantly reduced following chronic exposure to environmentally relevant concentrations of KClO 4 resulting in females with morphometric indices similar to those of control males - indicating potential sex-specific sensitivities to KClO 4 . Changes to reproductive indices (i.e., plasma androgen levels, gonadal thyroid hormone- and sex steroid-related transcript levels, and sperm motility) were also observed in both sexes and suggest that KClO 4 exposure may also have indirect secondary effects on the reproductive axes in male and female adult frogs. These effects were observed at concentrations at or below those reported in surface waters contaminated with ClO 4 - suggesting that this contaminant may have developmental and reproductive effects post-metamorphosis in natural amphibian populations., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

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. The model also closely fit independent data from another hummingbird, Archilochus colubris, suggesting that it is general enough to apply to other medium-sized, short-billed hummingbird species. When examined across the range of variation normally encountered by hummingbirds in nature, corolla length and nectar volume had the largest effect on nectar extraction rates. At corolla lengths longer than a hummingbird's bill handling time increases markedly. Hummingbirds maximize their net rate of energy intake by selecting flowers with the shortest corolla, the highest nectar concentrations and the highest nectar volume. Since there is a positive relation between bill length and nectar extraction rate, it is surprising that most hummingbirds have relatively short bills.

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. On average, all of the daily nectar production was cropped by the birds. We suggest that the supply/demand economics of coevolved mutualisms favour the evolution of complete resource use.

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. Our own experiments with Archilochus colubris support the conclusion that hummingbirds make foraging decisions that maximize NEVC. A simulation model shows that, in nature, NEVC maximization would require fewer foraging trips and visits to fewer flowers per day to balance daily energy budgets. For territorial birds this can lead to smaller territory sizes and reduced costs of territorial defense. Plants that evolutionarily increase corolla length to enhance pollinator specificity need only increase nectar concentration slightly to maintain the same net energy per unit volume consumed (NEVC) by a given hummingbird pollinator.

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. Adult survival was not affected by supplementary food, but young survival was higher than in 6 previous years and young seen to visit feeders may have survived better than young not seen at feeders. Young females were more variable in weight on the unfed half of the island than on the fed end. The breeding population increased by 38% from 1978 to 1979, but it is not known how much of this increase resulted from food addition. Pairs of birds with feeders on their territories began to lay 25 days earlier in 1979 than control pairs, but delayed longer than controls before a second breeding attempt. One-year old females began to lay significantly later than adults on the control area, but not on the fed area. Other measures of breeding performance were not affected by supplemental food. Winter food may be more important and male territorial behaviour less important than previously supposed in limiting numbers in the Mandarte Island Song Sparrow population.

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. We propose a new Status Signaling Hypothesis (SSH) suggesting that dull SY male plumage is a reliable signal of subordinate. We suggest that female choice based on male plumage color (as an index of male quality) is the selective mechanism that has favored subordinate status signaling by SY males. If females prefer bright males, then dull plumage may be a reliable signal of subordinance and SY males may experience reduced levels of aggression from adult males. Male characters (like plumage color) are most likely to be the object of female choice when males defend simple nesting territories with little or no variation in territory quality. In such a system, SY males with low resource-holding potential would benefit (via matings or experience) by signaling subordinance and being allowed to settle among more brightly colored adults. Thus, DPM is expected to be more prevalent when males defend simple nesting territories. This prediction of the SSH is supported by data from the literature-a significantly higher proportion of species with DPM defend simple nesting territories (versus all-purpose territories) than do species without DPM., (© 1986 The Society for the Study of Evolution.)