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May 9, 2011: Growing Fast--Are they all getting enought food?

May 9, 2011: Growing Fast--Are they all getting enought food?

Credit: Bob Sallinger

by Bob Sallinger

kgw.com

Posted on May 8, 2011 at 10:28 PM

Updated Wednesday, Oct 30 at 7:21 AM

The red-tail nestlings are now 17, 17 and 14 days old. Many people are writing in expressing concern about infrequent feedings, competition among the nestlings and the parents being away from the nest for extended periods. The behaviors the we are seeing at the nest are all within the range of what we would expect to see in a red-tail nest. The birds now have a thick layer of downy feathers and their body feather and flight feathers are starting to come in beneath the down---you can already see them starting to em merge through the downy feathers giving them an increasingly greyish-brown appearance (that and the fact that they are dirty). They are able the keep themselves warm (thermoregulate) on their own at this point and so the parents do not need to be right by their sides at all times. They do typically perch very close by to protect the young from predators, but they are often out of the range of the camera. The young can now go several hours without a visit from the parents.

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The competition between the young is also to be expected. The youngest bird is at a four day disadvantage and is often fed less than the other two siblings. It also looks like he may be a male which would give him an added disadvantage because red-tails are smaller than females.

Note the size disparity, but he is still right in there demanding to be fed. Photo by Krista Bradford

The thing to watch for is whether all of the bird's crops are full at the end of the feeding cycle.  The crop is a food storage pouch that is located near the top of the bird's esophagus. The parents actually cram quite a bit of food into the young each time there feed them---check out the size of the food bits relative to the size of the nestlings. The crop expands as the birds eat and the food is stored there and then slowly moves through the digestive system over the next couple of hours. (Think of it as a slow release system). With the young it means that the adults can feed a lot at once and rather than small bits non-stop. For adult birds, it allows them to eat wherever they find prey and then move on. Although the third nestling often appears to get less than the siblings, his crop is often bulging at the end of a feeding session. In the end however, there is no guarantee that all the young will make it---it is a tough world for them.

Peregrine falcons with full crops being raised at Audubon in 2007. Note the particularly full crops of the two birds on the left side of the picture and the bird on the right with the relatively empty crop screaming for more food. Photo by Bob Sallinger

 

 

 

 

 

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