Nesting effort of northern pintails in Alberta / Karla L. Guyn and Robert G. Clark.

Includes bibliographical references (pages 627-628).

We studied nesting effort and success of Northern Pintails (Anas acuta) in
southern Alberta. Annual nesting success estimates ranged from 6-18%. Clutch size averaged
7.2, and declined in a simple curvilinear fashion with nest initiation date. We found
no relationship between egg size and clutch size or evidence from one year to the next of
a trade-offb etweenc urrenta nd futurei nvestmenti n eggs. Within-yearr enestingr ater anged
from 55%, based on a sample of 20 decoy-trapped females that lost their first nests to
predators,t o 85% based on a sample of 13 nest-trappedfe males forced to renest when we
removed their clutches. Greater investment in initial clutches led to longer delays in laying
replacement clutches. Because delays in renesting are costly (late-nesting females produce
fewer offspring), females must contend with a trade-off between maximizing reproductive
output in initial clutches versus the risk of delayed renesting if the first clutch should fail.
We suggest thatp intailr eproductivetr aitsh ave evolved primarilyin responset o shortn esting
seasons and variable environments.