Do Female Northern Pintails, <em>Anas acuta</em>, Initiate Rapid Follicular Growth During Spring Migration?

We describe the reproductive status of female Northern Pintails ( Anas acuta ) staging on a flooded plain along the St. Lawrence River (Quebec, Canada) during the spring of 1997. Nine of the 27 female pintails we collected had ovarian follicles showing Rapid Follicular Growth (RFG). In RFG females, total blood calcium and ash mass increased with follicular development. They had greater muscle and bone mass, and higher blood calcium levels, compared to pre-RFG birds. However, carcass fat mass and sex hormone levels (estradiol and progesterone) did not differ between the two groups. Our results indicate that at least some Northern Pintails initiate egg formation processes prior to arrival at nesting areas, which is consistent with early nesting. The nutrients and energy required for this early egg formation must come from reserves stored during winter, foods consumed in staging areas, or both.