Caressing Mom's Beak
In this behavioral shot, one of two fledging great egrets at the rookery in York, Pennsylvania, is seen grasping the beak of a mature egret. I've seen similar behavior in great blue herons at the Venice rookery in Florida. What I think the youngsters are trying to do is to induce their parents to regurgitate a meal for them.
Do you have any thoughts on this?
Norm
I think you have it Norm. This is a food solicitation behaviour. It's a way the chicks can communicate to their parent that they are hungry. Siblings are competing against each other for feedings from the parent and a quiet, laid-back strategy would not win the evolutionary race against a sibling who aggressively goes after food. The other relevant thing to mention is parent-offspring conflict, which is a huge topic in evolutionary biology. When chicks get older, the evolutionary pathways of the parents and offspring split. For the parents, they have fed the chicks and the chicks have grown. This parental investment takes it's toll on their ability to produce chicks in future years. The parents want to cut the kids loose so that they have a good chance of being able to reproduce again. The kids don't want to leave because they want more for themselves rather than thinking about how many or the quality of future siblings they may have. Herein lies the conflict. It manifests itself often in very aggressive food begging by the chicks which does not lead to feedings as the parents are weening the kids off dependancy. As a side benefit, the fat chicks start to lose weight as a result of the weeing and this helps their flight performance in preparation for fledging.
I always think of an advert for butter which relates to this subject. Mum and Dad bid farewell to their son and remodel his room only to have him return to the "nest". They are clearly a little unhappy about this turn of events. Their strategy is to offer him margarine instead of butter for breakfast the next morning. This has the desired result- he leaves with rucksack over his shoulder!
John, I haven't seen that ad, but what a terrific analogy!Originally Posted by John Chardine
John: I haven't seen that ad, but appreciate the analogy.
One thing I noticed at the rookery as we were about to leave the area was that a number of the young egrets were able to fly and were flying down to the water and trying to fish. The woman from the rehab place said that the egrets support the young for some time after they have learned to fly. However, as she was releasing newly rehabbed, fledgling black crowned night-herons, she stated that once they had left the nest, they were on their own. The night-heron parents did not feed a chick on the ground or out of the nest area. I find that remarkable as they have to learn to fish all on their own -- and very quickly.
Linda
Yes Linda, some species care for their young after fledging and some don't. Some gull species do so for several weeks after fledging for example. Even though the egrets may support their young after fledging they probably still hold back feedings to encourage fledging to take place, and the parent-offspring conflict is probably still there, just delayed a little. You are right, it is amazing that young of many species have to figure out how and where to feed on their own. This is often a difficult process and mortality rates at this time can be quite high. This results in strong natural selection for individuals that are able to do this well.
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