Odd Blue Tit nesting behaviour (1 Viewer)

[John Mahon]

I wonder if anyone has encountered the same behaviour I've noticed recently in my nest box.
I've had a box fitted with a camera for some years and almost annually it is occupied by blue tits - this year however has seen some behaviour that I can't quite explain.

The female was joined in the box at night a week ago by what I assume is the male, who proceeded to roost on top of the female while she was incubating the 6 eggs. The first occasion I put down to the fact that the rain was torrential and the male wanted somewhere dry to roost. However the behaviour has been repeated nightly ever since and he appears to be quite aggressively trying to get to the eggs beneath the female as if to try and to incubate them himself!
This leads to a constant rummaging and battling with the female trying to stay in pole position and the worry is of course that the stress on the female will result in the eggs not hatching at all.

The thought had occurred that this is another female bird but I wouldn't have thought two females would tolerate each other in such close proximity.

I'm thinking this is unusual behaviour but am wondering if it's been observed by anyone else?

 

[delia todd]

How strange John.

Please keep us informed as to what happens.

 

[John Mahon]

Same again last night. Looking at the behaviour of the additional bird I'm wondering if it actually is a female as everything it's doing is mirroring what I've seen incubating females do over the years. It even appears to be covering the female beneath with its wings as if it's a fledgling chick!

Very odd.

 

[John Mahon]

After checking on the nest camera tonight it appears as though the eggs are hatching (5 out of 10 so far) and as well as the two females, a third bird presumably a male, is now joining in the feeding.
The jostling for position for incabation is still ongoing between the two females but the appearance of the male gives rise to various possibilities of either:

a) Both females mating with the same male and the resultant eggs being laid in the same nest or....

b) A female with an overbearing urge to mother has just jumped in and started co-incubating

....or maybe something completely different!

Either way, it's nothing I've seen before and it makes the nestcam viewing all the more interesting!

 

[John Mahon]

Checking on the nest this morning, all (seven or eight) young have died. Possibly connected with stress, as even up to last night the two females were fighting almost constantly over who was incubating.

Would be interesting to know if this is very unusual or if anyone else has experienced this behaviour with either Blue Tits or any other bird.

 

[etudiant]

Checking in to this thread very belatedly, it appears that Nature disposed of Solomonic justice. The babies were not shared, but divided.
From an ecological perspective, that is the desired result, it reduces the deranged mother contribution to the gene pool.
Wonder whether this is the kind of behavior that led to monogamy?