For the last two or three days I’ve been watching a couple of crows building a nest in a tree outside my bedroom window. They’ve got the nest pretty big now and it looks to be about ready (to my inexpert non-bird eye). But a few things about their behaviour made me wonder:
They spend all day building the nest. It looks to be quite hard work. Sometimes one of them will come back with a really big stick and really have to work to get it up to the nest (the nest is right up at the top of the tree, which is itself pretty big). When they come back with a big stick they start on the ground and then fly up to the nest in stages - first it will fly up to a wall, then onto the roof of a building, then up to a lower branch of the tree, then finally up to the nest.
So they’ve really invested some time and effort into this nest. But then at night they appear to desert it and go off somewhere else to sleep returning the next morning to carry on building. So is a nest more of an pure egg incubator than a home?
If the nest is an egg incubator, does that mean that the female is already pregnant and they are building the nest in preparation for the arrival of the little’uns? How does she know she’s pregnant?
The nest now is pretty big and well wedged in so it could probably withstand a good wind. But how do they start building it? They can only bring up one stick at a time so doesn’t that mean they have to leave one stick precariously balanced on a branch until they can get more up there to thatch it together? What stops the twigs blowing away before they can get the nest big enough?
The crows now “own” this tree. If any other birds try to land there they get chased away pretty quickly. Is this normal for birds to “own” the tree in which they build their nest?
Finally, although I’ve been watching them for a few days I haven’t noticed them today. It may just be that I’ve missed them but is it possible that they will put all this effort into building a big nest and then just abandon it? Why would they abandon it - better nest site somewhere else? Female realises she’s not pregnant? They forgot about it?
‘preganant’ isn’t really a relevant term for birds; they lay eggs - this will very often still take place even if they have not been properly fertilised by the male.
Birds use nests for the sole purpose of incubating the eggs and tending to the babies until they fledge. Nests are not homes, as such, and they do not build nests or live in them if it’s not the “time.”
The mother bird (and sometimes it is the father bird) will protect the eggs and the newly hatched. Have you walked under and near a tree and found a bird (grackle, crow, etc.) bitching at you? She (he) has a nest nearby and is warning you.
In winter, American crows leave territories each evening and fy to large communal roosts, which can include fish crows.
The nests of both the American and fish crows consist of twigs, sticks, lined with bark, grass, moss, and placed in trees. They lay 4-5 eggs. Incubation period is 18 days and 28-35 days after hatching, American crows fledge. It takes a little less time for fish crows. So I imagine they build a good foundation before they add heavy items.
Sometimes nests are abandoned and a new one built. Just recently I watched a white-eyed vireo build a nest in a well-hidden shrubbery at Caw-Caw County Park. The finished product was a work of beauty. However, she abandoned it. No eggs were ever laid in it. Why? It was in too obvious a place. Although well hidden, it was at the corner of two asphalt trails. In your case, it is possible that the crows noticed you watching them and decided that that location was not safe.
O.T. but beavers will build dams even if they are in a lake and have nothing to dam up. The behaviour seems to be instinctive. And squirrels quite often have two or more nests they live in. They like to build them and switch residences.
Outside my home office, under the eaves a nest was built rather recently and mama and papa were happily warming three fertilized eggs.
One or two days later, I heard a lot of screeching from birds…opened my office door to the outside and the bird’s nest was on the ground with 3 fractured eggs each of which had a dead embryo inside.
My question is as follows: We have both ground squirrels and wood rats living in the property and surrounding area. There are also coyotes, racoons, and even bobcats.
I felt badly about the entire situation. In all likelyhood which animal, if any, would have been the homewrecker with resultant embryo killing.