Blue Tit Shock - Utterly confusing (1 Viewer)

This might be long so sorry - but this is really confusing, and I think if anyone has the answer it will be Elizabeth bigg!

Ok - we put up a double house martin nest box three years ago. Nothing nested in it. Then this year, the right hand one had Blue Tits! We heard them chirping (the babies) and I saw one or two poking their heads out. They fledged without us noticing, and I guessed there were between 5 and 8.

Today I got the nest box down, and to my surprise there were nests in both nestboxes (left and right). I thought this was REALLY strange. Another Blue Tit pair were viewing the box at the same time as the other pair, but would they have nested within centimeters of each other?
Also, in the left hand side (no known nest until now) there were three eggs. In the right side (with babies heard and adults seen) there were FOUR eggs.
Is this normal mortality? And anyway, there were no dead babies in either side, so did the other pair nest at the same time? Did they abandon it, having just three eggs? Or did they nest another year. Surely we would have heard and/or seen them though.


In the "successful" nest, where we knew eggs hatched, wouldn't all the babies in a small area crush the four eggs? And wouldn't there be egg shells?



Something important i forgot - the right side, where we knew birds nested and had chicks - the nest did not have a "hole" in the middle, and seemed to have been done in a rush. There was also no faeces in there. In the left hand side, with apparently, until now, nothing - there was a "hole" thing in the middle of the nest, like normal, and seemed to have been done well. There WAS faeces in the bottom


HELP me please with this very confusing thing!

tp20uk said:

Today I got the nest box down, and to my surprise there were nests in both nestboxes (left and right). I thought this was REALLY strange. Another Blue Tit pair were viewing the box at the same time as the other pair, but would they have nested within centimeters of each other?
Also, in the left hand side (no known nest until now) there were three eggs. In the right side (with babies heard and adults seen) there were FOUR eggs.
Is this normal mortality? And anyway, there were no dead babies in either side, so did the other pair nest at the same time? Did they abandon it, having just three eggs? Or did they nest another year. Surely we would have heard and/or seen them though.
HELP!

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Blue tit broods had reduced in recent years because the species is going through a period of good fortune and the UK populationis increasing. Blue tits are known to adjust fecundity when there is little or greater pressures on the population. A few mild winters and good breeding successes depressed the brood sizes with most only laying four eggs in 2003. Unfortunately, there was massive total mortality of broods in 2003 and it was predicted (OK, why be modest? I predicted) that brood sizes would go up. Indeed, most people have reported from 6-8 (blue tits can go as high as 15 but 8-10 is the average) this year and with much greater success rates. However, out of a brood of 8, it is not unusual for only two birds to fledge and fewer still survive to maturity but that is another story. Mortality hits at various stages and is often directly related to food supplies and thus, air temperature. Four abandoned eggs would normally infer the birds had deserted at an early stage except that you say you heard youngsters. It would be unusual for two pairs to nest so close together and I wonder if this was one pair becoming confused and laying in both boxes. If they divided time between the clutches then this could explain the failure but does not explain why there were youngsters. Going off averages for 2004, 3 and 4 eggs would be under sized broods for this year but I cannot fully understand why they failed to hatch.

Thanks Ian, that helps a bit. But there are still so many unanswered questions! We need EB!

David - thanks for the compliment - but I don't think I can add much to the wisdom of an RSPB person!!!!

I think the eggs are pretty tough - after all they have to withstand the mother sitting on them, turning them and diving down to the bottom of the nest while doing the "housework". We found two unhatched eggs when we cleaned out the box one year (you'll be able to find details in our summaries, but I think this happened the first year we had a camera in a box). We never found eggshell left in the nest - this is disposed of soon after a chick hatches, either by the hen eating it, or removing it. This year in our one successful nest, the hen removed most of the shell - as far as we could tell, she only ate the last one hatched. In previous years quite a lot of the shell was eaten.

The only time we have seen faeces left in the nest was when the last couple of fledglings had left. Maybe the parents were too busy caring for the ones who had already left, to bother cleaning up during the last day.

Thanks to the excellent search facility here, I have been able to trace a thread I started earlier in the year - this is an even stranger story than yours:

http://www.birdforum.net/showthread.php?t=16608

Here 12 eggs hatched, but at this point one of the females vanished and the number of chciks dwindled daily until there were only 6 - then 3 vanished over night. The final three are thought to have fledged successfully.

If you are interested in reading more information about bluetits, see if you can get hold of a copy of British Tits, by Christopher Perrins. I managed to locate one a few years ago after a web search - when I rang the bookseller he was very anxious to tell me that it had a library plate inside it, so I suppose he must have thought I was a collector. I would not have minded what state it was in, though in fact it is in beautiful condition - obviously not of interest to people visiting the Devon county reference library!

www.biggonline.co.uk

Thanks very much elizabeth and ian!

Can anyone else help? Has anything similiar happened to you?

This may sound uttely stupid, but I am wondering if, in the odd occasion, that it is a "practice nest" and that the "real" one is built alongside? Ok I may be talking utter cobblers, but just a thought...

Interesting, though there were eggs in it, so i doubt it was a practise. but still. to avoid anything like this, i have moved on of the house martin nestboxes to the front of the house. there are now two singles. also the standard nestbox on the tree has been moved. not sure if i mentioned this before - it ALSO had a nest, and only one egg, though i never cleaned it so could have been old. my mum said she saw birds going in and out, but gave up?? i wasnt into birds at that time, so i dont know.
this has been cleaned, nest box plate added, and fixed on garage in back garden.
its very close to the house martin nest box though. Do you think the blue tits will come back the the h/m nestbox? if not, will they use the hole nest box? or one at all?

hole nestbox replaced with new hole nestbox, and large bird nestbox a few metres above it.