I have some real problems, Rose. A few minutes after I wrote my last post, I went out to put the sparrow spooker on the box. As I approached the nest box I saw part of a blue egg on the ground in front of the nest box. It was broken and most of the yellow yoke was still in the egg shell. Needless to say, both bluebirds are very upset. An hour later Papa was trying to feed Mama a worm and she simply refused to take it. After he left she just sat there for a good 5 minutes, seemingly devastated. First Dave removes her nest with 5 eggs, then this.
It seems very strange that this egg was removed only an hour or two after it was laid.
My first thought was HOSPs, since I am literally over run with them. But the more I think about it I wonder if it might have been a cowbird. A HOSP would have invaded if he wanted to take over the nest box and most likely would have broken the egg in the nest and he definitely would have torn up the nest. But this nest was hardly disturbed.
I have read a lot lately that cowbirds can be vindictive towards birds that remove one of the cowbird's eggs from the nest; that they seem to remember and come back to punish the birds that did it. Usually the punishment is removing a nestling and flying off with it. They sometimes remove an egg too, most notably when they substitute one of theirs.
Yesterday afternoon a female cowbird was snooping around the nest box. I was surprised that with the slotted opening she was easily able to squeeze inside. She was nearly all the way in when Papa Blue came out of nowhere, like a linebacker. The cowbird did not see him until the last second and he hit her broadside, feet first, and with an audible thud. He usually buzzes the birds, so she may have moved up into his path. It all happened before I could pick up my camera. But I'm sure it is something she would remember.
I wonder if I should change the opening. I have a door with a regular 1 1/2 inch round opening that I could pop on in a matter of a few minutes. I'd sure hate to lose a second egg.
But would this additional change totally drive the blues to distraction?
UPDATE: It is now after1:00 a.m. and I just went out there and removed the slotted front and installed one with a regular 1 1/2 inch round hole opening. I also removed about 2 inches of nesting material from the bottom of her nest. It may still be too high. It should be interesting when she shows up tomorrow. I know bluebirds are tolerant of human interference. This should test their tolerance to the limit. I sure hope they accept it.
This message was edited Apr 26, 2009 1:24 AM
