==================+=================================================== | Occurrence of Peak of Egg-laying +-------------------+------------------------------- | When | When Mean | Precipitation is: | Temperature (F.) is: +---------+---------+-------+-------+-------+------- | Light | Heavy | < 55° | < 70° | ± 70° | > 70° ------------------+---------+---------+-------+-------+-------+------- Raptors | x | | x | | | O. W. Element | x | | x | | | Residents | x | | | x | | Grassland species | x | | | x | | Marshland species | | x | | | x | N. Amer. Element | | x | | | x | Migrants | | x | | | x | Woodland species | | x | | | | x Aerial foragers | | x | | | | x S. Amer. Element | | x | | | | x ------------------+---------+---------+-------+-------+-------+------- None of the regulators mentioned above has been specifically investigated for any Kansan bird, but it is reasonable to suppose that, in these temperate-zone species, the photoperiod is the most important general phasing factor in seasonal breeding. Although gonadal response and seasonal restriction of breeding are set by the photoperiod, specific temporal relationships are dictated by more immediate environmental variables. Table 9, as already noted, shows the gross relationships between certain groups of birds, certain arbitrary indicators of seasonal temperature-humidity conditions bearing significantly on the growing season, and occurrence in time of peak of egg-laying by the birds involved. Some species and groups of Kansan birds breed chiefly under cool-dry environmental conditions, and some under warm-wet environmental conditions. Within each of these categories some variation occurs. Thus, raptors and boreally-adapted species (the Eurasian zoogeographic element) breed under cool conditions prior to rains, and residents and grassland species breed under slightly warmer conditions prior to rains; limnic species, species derived from North American evolutionary stocks, and migrants tend to breed in the cooler segment of the warm-wet period, and woodland birds, aerial foragers, and species derived from South American evolutionary stocks tend to breed in the warmer segment of the warm-wet period.