For the past two springs I have watched juncos defend territories and have
>not seen any sign of nesting. Maybe I am incorrectly identifying the
>behavior. But I recognize the song and I watch them chase each other and
>other species, around the yard. Do juncos aquire mates on their wintering
>territories and then go elsewhere and breed?
>
>
>Jim Rosso
>Issaquah

The hormones that get birds prepared for breeding don't wait until the
breeding season. Their production is stimulated by the increased day
length, and they then stimulate feeding bouts that put on fat for migration
and the migration itself. They further stimulate song and territorial
behavior and the increase in testis size in preparation for breeding. One
consequence of this is that, as spring moves inexorably closer, male birds
become increasingly aggressive even in their winter flocks. The same
thing's happening in my yard with the juncos.

Dennis Paulson, Director phone: (206) 756-3798
Slater Museum of Natural History fax: (206) 756-3352
University of Puget Sound e-mail: dpaulson at ups.edu
Tacoma, WA 98416