Burke Museum - 3 - Treachery

Lat:47.66063861939029, Lon:-122.31028240171611
Day, 2012
4/26/12
1:30-3:30

Today we visited the Burke Museum for the second time. We looked at three zones: treachery, death, and sex. In the treachery section we looked at Weaver eggs. Some of the eggs were blue, red-spotted, white, etc. There was so much variation because it is easy to put your eggs into another nest in order for them to be raised by other parents (parasitizing that nest).

An interesting side note is that the females lay the same color egg regardless of the male. This makes it easy for her to keep track of which eggs are actually hers.

One species that does this a lot is the brown cowbird. They lay about one egg per day but don't make nests. They are the only North American bird that doesn't raise their own young. Once the eggs are laid, they are all put into other nests (for example a warbler' nest). The eggs of brown cowbirds are about 30% harder than most other eggs which makes it risky for the parasitized nest birds to pierce (because they risk bouncing off the hard cowbird eggs and ricocheting onto one of their own). Another reason why parasitizing works for these birds is known as the "Mafia hypothesis." The Mafia hypothesis states that cowbirds kill the warbler babies if the warbler parents try to get rid of the cowbird babies or make new nests on top of parasitized nests. Once the cowbird babies have matured, the parents can actually call them back.

This whole phenomenon was really interesting to me. I had never heard of a bird that just drops their young off onto someone else. It seems like a whole lot of work though. If you think about all the eggs they lay and all the nests they drop their eggs in, keeping up with all of that must be really difficult. Also, the time these cowbirds put into making sure the nests they parasitized are still housing their young must be pretty substantial. This makes me wonder why they don’t just make a huge nest of a whole bunch and raise their young on their own. If they are the only species in North America that does this, it seems to me that this is definitely not the best way all other North American birds have come up with.

Species List:
Weavers
Brown cowbird
Warblers

Publicado el mayo 25, 2012 09:35 TARDE por lisad22