>If birds can raise two or three clutches in one place in a season why not
>two in two places?
>
>Gene Hunn

(1) Territory establishment may take quite a long time, even a month or
more. To have to do it twice in a year would be very demanding.

(2) Parental care may extend to young of the first clutch even while the
adults are preparing physiologically for the second clutch.

(3) Migration is both energetically demanding and dangerous, so there would
have to be a substantial gain in fitness by moving to a second area rather
than staying in the first one, which means there would have to be
substantially better conditions in the second area. Not impossible,
perhaps just unlikely, without moving quite a distance from where you
already are.

Most of the birds that raise more than one clutch are residents, which
start quite early in the season, although some migrants manage to do it
too.

Dennis Paulson 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