(This will be a regular feature: blurbs about papers I like.)
Today’s paper: “The process and causes of fledging in a cavity-nesting passerine bird, the House Wren (Troglodytes aedon)” by L. Scott Johnson, Robin L. Rauch, and Sara N. Dellone. Published in 2004 in Ethology 110, pages 693-705.
Fledging is the act of leaving the nest for the first time. In birds with altricial (helpless, naked, dependent) young, this is a big step: the chicks go from sitting in a nest to flying around like adult birds. Or trying to fly around, anyway. Fledglings often aren’t very good at flying at first.
I’ll admit I have a soft spot for House Wrens, but this paper would be neat no matter what the species was. Johnson et al. videotaped House Wren nestboxes, then watched the videos to determine what fledging really looks like. They found that most fledging happens early in the morning, and that most chicks in the same nest all fledge on the same day. The parents don’t appear to tell the chicks when to fledge; instead, the biggest chick fledges, and then all of his nestmates follow. This can be real problem if you’re a runt: your big brother or sister fledges, and you follow, but your wing muscles aren’t as well-developed yet and you won’t have as much fat stored. Other studies have found that chicks that fledge small survive less well than chicks that fledge large.
The paper has some wonderful observations. There are the accidental fledgings (“nestlings attempted to step onto the perch but missed… [and] fluttered to the ground”) and the forced fledgings (“four nestlings… were clearly pushed out of nests by parents or a nestmate”); there are nestlings that fly out of the nest, nestlings that fall out, and the nestlings that “started to fly or fall but hesitated and ended up hanging below the nest entrance by one leg.”