Geographic Variation in the Placement and Structure of Oriole Nests

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Abstract
The placement and structure of the nests of the northern oriole [Icterus galbula] vary geographically, mainly because of differences in vegetation, and in response to variation in environmental conditions such as wind and the abundance of predators. Nests in the northeast are built on thinner branches, presumably to make them less accessible to squirrels. Nests in the southwest (Oklahoma Panhandle [USA], SW Kansas [USA]) are better protected from the rays of the sun; they have a smaller opening and are more spacious (although the latter may reflect size differences in the birds themselves, or geographic variation in clutch size) than those in the northeast. Texas Panhandle [USA] nests are an exception, possibly because the mesquite trees provide more shade and larger openings of these nests may be more amenable to heat dissipation. The southwest nests are also placed more securely in the trees. At certain localities the compass direction of placement may be significant with respect to wind stress. The nests of the orchard oriole [I. sparius] do not, in general, reflect the same trends found for the northern oriole. The orchard oriole may build a nest with a wider opening, or place it beyond the insulating effects of the surrounding vegetation, in places where the heat stress is likely to occur.

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