Tuesday, May 22, 2012

Egret and Pelican Rookery: Feeding Time

I think that feeding the chicks is the most difficult and energy-requiring task of the adult parent. Having seen many great egret chick feedings, it can also be concluded that it is risky and can cause significant injury to both chick and parent. Upon closer inspection of photos, one can see peck wounds along the beaks of adults and chicks. And no wonder, the great white egret beak is a weapon.

With more than one chick to feed, there is a constant battle. I learned that birds secret the hormone corticosterone (a stress hormone) that stimulates begging (most likely it stimulates hunger), which in turn increases parent provisioning (obesity in humans is correlated with cortisol levels, I wonder if there is a connection). Nevertheless, the success of feeding depends not only on prey density but also on this hormone. One chick often dominates and is fed more successfully than the smaller sibling(s). The parent flies in and does not begin the feeding right away. Rather, the adult will stand over the chicks that are begging and jutting their necks upward toward the adult's face. The adult stands erect and it is as if it is teasing the little ones that are working hard to get closer to the adult's beak. A chick will finally reach the adult's beak and within a split second, the adult is pulled downward with chick attached, beak to beak. The second or third chick will attempt to get in there and as seen in the photo below, both are clamped onto the adult while regurgitated food is transferred to the chick.

After about a minute of this, the adult will pull away and resume its erect position. Mean time, the siblings squabble and then commence with the begging. The process repeats itself a few times before the parent has enough and flies off leaving the little beggers behind.

Pelican feeding does not appear as violent. Instead, the chick can place its entire head into the adult's poach. Below are two photos of a rather large juvenile getting fed by its parent. It looked as if the chick did not have any siblings. This is a good thing for the chick because without competition, it will receive all the food and learning opportunities from the parent. Bon Apetit, petit oiseau!

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