Sunday, May 17, 2009

Something Strange Afoot in Phoebe Nest

Posted by Kirk
As noted a few days ago, we were up to 7 eggs in the Eastern Phoebe nest at work after a Brown-headed Cowbird added two eggs to the nest. Weirdly, on Friday there were suddenly only 6 eggs in the nest. mn-warnerEastern Phoebes are not known to remove cowbird eggs so this seemed strange. I took a look on the big monitor we have in our lab downstairs. The lab feed is a direct live video feed of the nest and the image is larger than the stills we can pull from the feed we send to Cornell. I could clearly see that the two cowbird eggs were still in the nest. It was a phoebe egg that was missing. I next looked out the window near the nest and sure enough I could see a broken smashed egg on the ground under the nest. On Saturday, I taught a group of girl scouts and at the end of class we stopped by the monitor so I could tell them about the nest monitoring project and how they can take part. How's this for weird, there's another egg missing from the nest. I could see on Saturday that there were only 5 eggs in the nest. The cowbird eggs are still there but there are only 3 phoebe eggs now.

mn-warner-1
Did she knock them out on purpose? Was it an accident? Did the cowbird return and destroy some of her eggs for some reason? To try to find out I turned to the time lapse videos of the nest on YouTube. On Saturday evening, all six eggs are there at 5:57:19.

Picture+4
She returns at 6:03. She moves around a bit and has her head down by the eggs. There is no sign of a cowbird visiting the nest. When she leaves again at 6:11, just 8 minutes later, the sixth egg is gone and there are only 5 in the nest. The one in the upper left, which was closest to her head, is gone.

Picture+3
Did she eject the egg on purpose then because she thought the nest was too crowded? One clue may be this image from the same evening at 5:44. Is that an egg she's pushing up toward the edge? Maybe she tried to push it out earlier and was unsuccessful but got it right half and hour later.

Picture+1
If I get time I may try to figure out when the first egg went missing and see if anything shows up on the images.

~Kirk

1 comments:

anika said...

Might not be happening in this case, but I've heard of predators taking one or two eggs at a time. However, I've only heard about that with species with larger eggs, like waterfowl...hard to imagine a single phoebe egg making much of a meal!