Testosterone and avian life histories: effects of experimentally elevated testosterone on prebasic molt and survival in male Dark-eyed Juncos

Article Abstract:

The physiological trade-off between reproduction and molting was investigated by implanting male Dark-eyed Juncos (Junco hyemalis) with testosterone (T) to prolong the reproductive condition and delay molting. High T levels maintained until late in the breeding season resulted in delayed but completed molt. High T levels maintained long after the breeding season resulted in failure to molt and low return rates in the next breeding season. Further studies are suggested to separate the effects of high T from other factors on overwinter mortality rates.

Testosterone, Molting, Junco hyemalis

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Carcass mass, composition and gut morphology dynamics of Mottled Ducks in fall and winter in Louisiana

Article Abstract:

Carcass mass, composition, and gut morphology were studied in Mottled Ducks (Anas fulvigula), a species that had eliminated migration from its annual cycle because of the mild climate in their habitat. During fall to late winter, males and females replenished endogenous mass and reserves used up in reproduction and in molting. This replenishment is in preparation for the early breeding opportunities which the species avails of because of its non-migratory status.

Ducks

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Spatial aspects of roost-site selection in breeding male dark-eyed juncos

Article Abstract:

A study of breeding male Dark-eyed juncos at Mountain Lake Biological Station, Giles County, VA, revealed their use of coniferous trees for roosting and their behavior of frequently shifting roost sites to escape predation. Off-territory roosts are integral parts of territorial intrusions by male juncos.

Research, Analysis, Prevention, Predation (Biology), Spatial behavior in animals, Animal spatial behavior, Juncos

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