Seasonal and Taxonomic Differences in the Size and Activity of the Thyroid Glands in Birds

Author Institution: University of Illinois, Champaign, and Metropolitan Park District, Cleveland, OhioThe thyroid glands of the house sparrow and other small birds in the Cleveland region have greater secretory activity during late autumn and winter than during late spring and summer. Evidence for this is the presence, during the winter, of high epithelial cells surrounding the follicles, of smaller follicles, and of lesser volumes and weights of the whole thyroid. Large-sized species have larger thyroids, both absolute and relative to body weight, than do small species. With certain precautions, changes in the size of the thyroids serve as a useful index of inverse variations in secretory activity intra-specifically, but not inter-specifically

Testing an Emerging Paradigm in Migration Ecology Shows Surprising Differences in Efficiency between Flight Modes

To maximize fitness, flying animals should maximize flight speed while minimizing energetic expenditure. Soaring speeds of large-bodied birds are determined by flight routes and tradeoffs between minimizing time and energetic costs. Large raptors migrating in eastern North America predominantly glide between thermals that provide lift or soar along slopes or ridgelines using orographic lift (slope soaring). It is usually assumed that slope soaring is faster than thermal gliding because forward progress is constant compared to interrupted progress when birds pause to regain altitude in thermals. We tested this slope-soaring hypothesis using high-frequency GPS-GSM telemetry devices to track golden eagles during northbound migration. In contrast to expectations, flight speed was slower when slope soaring and eagles also were diverted from their migratory path, incurring possible energetic costs and reducing speed of progress towards a migratory endpoint. When gliding between thermals, eagles stayed on track and fast gliding speeds compensated for lack of progress during thermal soaring. When thermals were not available, eagles minimized migration time, not energy, by choosing energetically expensive slope soaring instead of waiting for thermals to develop. Sites suited to slope soaring include ridges preferred for wind-energy generation, thus avian risk of collision with wind turbines is associated with evolutionary trade-offs required to maximize fitness of time-minimizing migratory raptors

Animal Ecology

468 tr. ; 28 cm

Ecology : With Special reference to Animals and Man

New Delhivi, 472 p.: illus.; 28 c

Energy Responses of Birds to Their Thermal Environments

Volume: 81Start Page: 441End Page: 44

Regulation of Nesting Time and Distribution in the House Wren

Volume: 75Start Page: 418End Page: 42