Effects of Extended Tropical Photoperiod and Temperature on the Dickcissel

Publisher Website
Google Scholar
Abstract
The timing of premigratory fat deposition, "Zugunruhe," and molt in Dickcissels maintained for an extended period at photoperiod and temperature conditions of their contranuptial area was compared with the occurrence of these events in control birds held outdoors on both their tropical wintering and north-temperate breeding ranges. Under these constant environmental conditions Zugunruhe was maintained in phase with the controls for 1 year, while premigratory fat deposition was still in phase after the end of a year. Molting was not eliminated in the majority of birds until after one year in the experimental environment. It is concluded that the control of all these events is largely internally regulated and that the eventual elimination of these phenomena is temporally related, not to time since resident on the nesting range, but to the time since introduction into the constant environment, wnether from the wintering or breeding area.