Green cones of the piñon pine stimulate late summer breeding in the piñon jay
Abstract
REPRODUCTION in birds is influenced by a variety of environmental factors, usually classified as ultimate or proximate1. Ultimate factors determine efficiency of breeding, for example food supply for the young both before and after they become independent of their parents. Proximate factors, on the other hand, are the timers or predictors which initiate breeding at the appropriate time. Photoperiod is the most reliable and common proximate factor in those temperate zone species which breed exclusively in spring when daylength is increasing2. Other proximate factors, such as rainfall, provide predictive information in many regions of the world, in that increased food availability follows the rains3.
- Publication:
-
Nature
- Pub Date:
- July 1974
- DOI:
- Bibcode:
- 1974Natur.250...80L