JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. . Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology.Abstract. During the summers of 1968-1975 the breeding biology of a color-marked population of goldfinches was studied in natural, nursery, and city habitats at Guelph, Ontario, Canada.Nesting began in early July, the mean date for the laying of the first egg laid each year varying by only 7 days and the mean date for the 1st egg of all 1st clutches by 2.6 days. Old Y Y (birds in their 2nd breeding season or older) were mainly responsible for early nesting, and the percentage of such birds involved with breeding became less as the season progressed. The height of nesting occurred in the latter half of July, and no new nests were begun after August.The largest clutches (mean 5.3 eggs) were laid by old Y Y, which in turn laid a higher percentage of 6-and-7-egg clutches than did presumed 1st-year birds. The age of the d may also influence clutchsize since the largest recorded clutches (mean 5.6 eggs) belonged to old d d paired with old Y Y. Habitat also affected clutch-size, the nursery having the highest (5.6 eggs) which was followed by the city (5.2 eggs) and finally by the natural habitat (5.0 eggs). The differences in clutch-size may have been influenced by the age structure of the breeding populations in each habitat, by differences in time of nesting and breeding population density, and by effects of cowbird parasitism. Clutch-size diminished with season, July clutches being significantly larger than August clutches. Nesting records suggest that 6.0 eggs forms the most productive clutch-size for the American Goldfinch. Old Y Y had a higher success, both in terms of numbers of young fledged/nest and ratio of successful nests, than presumed 1st-time nesters. Age of & & may also affect nesting success, as in matings between old d d and old Y Y all chicks that hatched fledged, and a greater number of fertile eggs was produced in this mating combination than in any other.Fledging and nesting success were highest in the city, followed by the natural and nursery areas. City nests suffered a lower predation rate than those in the other 2 habitats, but a higher percentage of city nests was abandoned. Overall, the city was the most successful nesting habitat.In the natural habitat 74. 1% of nests were built in shrubs, trees being used exclusively in the nursery and city. Maple was the most commonly used tree in all 3 habitats; whereas 67.9% of all nests built in maple failed in the natural area, only 22.2% failed in the city. Heights above ground at which nests were built also increased with reliance on trees. City nests were significantly higher than those in the other 2 habita...

The plasma concentration of prolactin was measured following experimental photostimulation, during oviposition and during incubation in plasma from ruffed grouse by heterologous double-antibody radioimmunoassay. A slight increase in plasma prolactin was noted after photo-stimulation and a much larger increase was observed as subsequent eggs were laid. When the last egg was laid, plasma prolactin was maximal. This high concentration was maintained throughout incubation and declined to basal values when incubation was terminated by removal of the eggs. In hens that failed to incubate, plasma prolactin declined after the last oviposition.Brood patch development began before the first egg was laid but was not completed until incubation was initiated. Therefore, the patch began to develop when plasma concentrations of prolactin were slightly elevated but it was not fully formed until high concentrations of prolactin were maintained for several days.

No abstract

No abstract

An analysis of the spermatogenic condition and of the weights of testes from about 450 brown-headed cowbirds (Molothrus ater) was made to determine the annual cycle of this species at London, Ontario, and to ascertain variation in the cycle due to age. Testes of birds more than 1 year old (adult) reached maximal weights in late April and early May coincident with the beginning of egg-laying, and about 3 weeks before the testes of 1-year-old birds (yearlings) reached their maximal weight. The mean weights of testes of adults were usually greater, often significantly so, than those of yearlings. From about May 23 to June 23 there were no statistically significant differences in the weights of testes from the two age groups. Beginning in late June, the weights of testes declined rapidly in both age groups and reached a minimum in August. Minimal weights of testes persisted in captive birds until February.Large amounts of sperm were present in the testes of adults in mid-April and of yearlings in late April well in advance of maximal testicular weights. Sperm production occurred in most birds until early July but had ceased in most by late July.Testes, apparently undergoing regression, were noted significantly (p <.005) more frequently in adults than in yearlings in May and early June at the height of the breeding season. The significance of this observation and some aspects of testicular regression, previously unrecorded, are discussed. Adult birds are more sedentary than most yearlings in the breeding season and, unlike the latter, habitually associate with the same female. These behavioral differences may be related to the observed differences between the age groups in the testicular cycle.