Zoogeographic Categories Three categories of Mayr (1946) are of use in analyzing trends in breeding schedules of birds in Kansas. These categories of presumed ultimate evolutionary origin are the "Old World Element," the "North American Element," and the "South American Element." Not always have I agreed with Mayr's assignments of species to these categories, and such differences are noted. There is some obvious overlap between these categories and those discussed previously. _Old World Element_ Eighteen species, Red-tailed Hawk, Rock Dove, Great Horned Owl, Hairy Woodpecker, Downy Woodpecker, Black-billed Magpie, Common Crow, Black-capped Chickadee, Tufted Titmouse, Robin, Loggerhead Shrike, Starling, House Sparrow, Bank Swallow, Barn Swallow, and Blue-gray Gnatcatcher, furnish 969 records of breeding (Fig. 1). Species for which I have records but which are not here listed are the Blue Jay and the Wood Thrush, both of which I consider to be better placed with the North American Element. The distribution of completed clutches runs from mid-January to the first third of August, and shows a tendency toward bimodality. The second, smaller peak is due to the inclusion of relatively large samples of three migrant species (Robin, Bank Swallow, and Barn Swallow). The timing of the breeding seasons of these three species is in every respect like that of most other migrants; if they are removed from the present sample the bimodality disappears, indicating an increase in homogeneity of the unit. _North American Element_ Twenty-six species, Greater Prairie Chicken, Bobwhite, "flicker," Rough-winged Swallow, Purple Martin, Blue Jay, Carolina Wren, Bewick Wren, House Wren, Mockingbird, Catbird, Brown Thrasher, Wood Thrush, Bell Vireo, Warbling Vireo, Prothonotary Warbler, Yellow Warbler, Chat, Eastern Meadowlark, Western Meadowlark, Red-winged Blackbird, Orchard Oriole, Baltimore Oriole, Common Grackle, Lark Sparrow, and Field Sparrow, furnish 1,233 records of breeding (Fig. 1). The distribution of completed clutches runs from the first third of April to the first third of September. The modal date for completion of clutches is June 1. _South American Element_ Twelve species, Eastern Kingbird, Western Kingbird, Scissor-tailed Flycatcher, Great Crested Flycatcher, Yellow-bellied Flycatcher, Traill Flycatcher, Eastern Wood Pewee, Eastern Phoebe, Cardinal, Black-headed Grosbeak, Rose-breasted Grosbeak, and Indigo Bunting, furnish 552 records of breeding (Fig. 1). The curve representing this summary schedule is bimodal, wholly as a result of including the Eastern Phoebe and the Cardinal with this sample. _Relationship of Schedules to Temperature and Precipitation_