bluetit dies laying eggs

[annasig]

Hi, can anyone help me please. Bluetits spent weeks making nest in nesting box with camera. Made fantastic viewing. Female was in nest every night for a good few hours. Suddenly last night she stood up (I watched it happen, it was very sad) and just keeled over, dead.
Does anyone have any clue what may have happened.

[valleyforge]

Hi annasig and welcome to the WAB forum.

I'm sure that this was distressing for you to have witnessed, and although we can never be certain exactly what caused its death, perhaps I might be able to shed some light on some probable reasons.

In a nesting scenario such as this, a very likely cause of death may be related to the inability of the (presumed) female bird to pass an egg ... this is known as 'egg-binding' ... or alternately a thin-shelled egg may have burst inside her.

A bound egg inevitably leads to heart failure, whilst a burst egg causes death from peritonitis. For both the onset of death is sudden.

Although the underlying causes for these symptoms are many and varied, there are a couple of things that are frequently implicated.

The first of these is hypocalcemia ... effectively a fatal lowering of blood calcium levels ... which is often caused by a dietary imbalance of calcium, phosphorus and/or vitamin D3. Calcium is needed to build the shells of eggs of course, but it is also required within the body in order for muscles to work properly. If the bird had insufficient supplies of calcium to draw upon, then it would face the dual problems of producing shells with an inadequate thickness to be laid safely, whilst also having insufficient muscle control/strength to push the formed egg out of her oviduct.

Dietary imbalance is of course a major problem which can beset many of our common garden birds, particularly within rural and suburban gardens ... because they are there only because we provide them with supplementary foodstuffs on our bird tables.

However, the very foods that we tend to provide them can lead to hypocalcemia, since both peanuts and sunflower kernals contain chemicals that inhibit somewhat the ability of the bird's body to release calcium when needed.

In soft-water parts of the country, where soluble calcium may not be readily available in natural or provided water, or in calcareous plants, then birds can be put in some jeopardy by what we think we are providing to keep them alive.

A second possible problem that may be implicated here, bearing in mind the recent spell of particularly good weather, is that thin-shelled eggs tend to be laid in very hot weather.

Hyperventilation (heavy-breathing) by the bird to overcome over-heating leads to something called respiratory alkalosis. This results in a lowering of the partial pressure of carbon dioxide in the blood, with the outcome that fewer calcium ions are available to the cells of the shell-gland.

As I said though, these are only possibilities based on my experience of some casualty birds that we sometimes get during the breeding season ... older females, or first-time breeders, tend to be much more susceptible.

To try to alleviate these problems arising here, we always put out some layers mash (a powdered poultry food containing calcium) on the feeder tables during the breeding season, and also ensure of course that the tit nesting boxes are positioned in shade out of direct sunshine and can't overheat.

[annasig]

Thank you for taking the time to give such a lengthy reply. I understand more now about the possible causes. I couldn't believe what happened. I was just watching quite happily when it suddenly died. I am absolutely devastated as I felt I knew her, and now I feel so sorry for her partner. This is a brand new birdbox that I got for Christmas and I felt so privileged that the birds had come to nest in it.
Should I now remove bird and nest, or should I just remove the bird? Do you think the box could be used again this season?
Thank you so much for your help, it is very much appreciated.

[valleyforge]

It is still early in the season, so it is still possible that the box may be used this year by another pair ... or by the male and a new mate.

Remove the dead bird using disposible gloves and dispose of the body by burial (at least one foot deep) or incineration, just in case the cause of death was disease.

You haven't mentioned that there are any eggs, so I'm assuming there are none.

Provided you can't see any evidence of fleas or mites in the nest material, then I'd be inclined to leave it ... future occupants will decide if they want to keep anything or remove it all. If the box remains unused after July, then the box can be emptied/disinfected ready for over-winter roosting and nesting next season.

[annasig]

Thank you so much for all the info. I think I can see one egg but not sure. I will follow your valued instructions and see what happens. The box is north facing, so I son't think over-heating could be the problem.
Thanks again, Anna

[Wild-Woman]

A sad situation but some first class information from Valley Forge which I'm certain we will all benefit from. So you could say that your little blue tit didn't die in vain, now we all know how to help out our own garden friends.

[bigdave60dog]

This may be the sort of thing that is causing such a decline in some bird species.
Blue Tits being one.
But for your observation this would go undocumented.
Dave

[RKB]

Originally Posted by bigdave60dog

This may be the sort of thing that is causing such a decline in some bird species.
Blue Tits being one.
But for your observation this would go undocumented.
Dave

Blue Tits have increased by a third since the 1960s. They're one of the most increased garden birds.

[RKB]

Originally Posted by valleyforge

It is still early in the season, so it is still possible that the box may be used this year by another pair ... or by the male and a new mate.

Depends where you are. This is the earliest breeding season on record in many places, and birds in southern-central England already have young, so it's getting late there.

Originally Posted by valleyforge

Remove the dead bird using disposible gloves and dispose of the body by burial (at least one foot deep) or incineration, just in case the cause of death was disease.

I think that's probably a bit extreme. None of the likely diseases are going to be transmissable to other birds or humans after death. I'd remove the bird and any eggs and bung them under a bush. Something else might as well eat them, even if it's insects.

Originally Posted by valleyforge

If the box remains unused after July, then the box can be emptied/disinfected ready for over-winter roosting and nesting next season.

Again, you don't really need to disinfect anything, or remove nesting material. The birds are capable of handling that themselves. The idea that you need to disinfect nestboxes is a bit of a marketing gimmick. Blue Tits re-use natural sites year in and year out with no obvious problems.

[annasig]

Thank you all for your input. I am based in Central Scotland, so hopefully there might be still time for more activity this year. Will keep you all posted.