Socially monogamous birds have provided a major focus of research in the field of sexual
selection, providing insight into the evolution of ornaments, sexual dimorphism and sex …

Migration, broadly defined as directional movement to take advantage of spatially distributed
resources, is a dramatic behaviour and an important component of many life histories that …

Migrant species express wide varieties of movement strategies that closely mirror patterns of
resource distribution. Resources can vary predictably in space and time (eg, seasonal peaks …

Climate change has altered the timing of recurring biological cycles in both plants and
animals. Phenological changes may be unequal within and among trophic levels, potentially …

Ultimate factors such as food availability and weather create optimal windows of time for
birds to reproduce. However, within a given year, birds must rely upon proximate …

Comparative endocrinology is a fascinating field of science in part because it addresses
both ultimate and proximate causation. Research on sexual dimorphism and sexual …

Date and latitude interact to determine photoperiod, the daily period of daylight. This
interaction has important implications for latitudinal migrants for whom daylight may be a …

Animals' lives are typically subdivided into distinct stages, some of which (eg breeding)
contribute to fitness through enhancing current reproductive success, and some of which (eg …

The preservation of delicate structures such as feathers is very rare in the paleontological
record, due to the fragility of their components. Fossil feathers have been reported from …

Yearly, testosterone (T) levels fluctuate as many vertebrates cycle through reproductive and
non-reproductive periods. Among many temperate birds, it is well established that levels of T …