I’ve had huge successes the past couple of years with my garden Tree Sparrows, but this year, I fear that they might not be doing quite as well.  I admit I’m yet to open the boxes, but the lack of activity around all three boxes suggests that for some reason the broods have all failed.

There are a variety of reasons why birds fail to breed successfully, even in sites and boxes like mine that have produced several broods of young in previous years. It’s sad when it happens, but in most instances it’s a natural event and just has to be accepted. Last year my three boxes produced close to 30 young Tree Sparrows, hopefully that’s enough to compensate for the losses this year and it’s not too late for a second breeding attempt.

When I open the boxes, I’ll probably have a better idea of the cause of failure.  Of course I could have added a camera to keep an eye on them and watch them develop – perhaps I’ll do that next year!  This did get me thinking about the cause of nest box failures though, some of which I have shared below.

Rain

Weather plays a huge part in the success or failure of most breeding birds. A late cold spell can chill eggs and heavy rain over several days can have exactly the same effect. Even in the best made nest boxes water can find its way into the box and cause eggs or very young birds to become chilled. Perhaps a wet period this Spring did this for the Tree Sparrows in my garden.

There isn’t much you can do about the weather, but you can position your nest boxes away from the prevailing wind direction so that the rain isn’t driven in.  Shelter them a little by siting the box on a tree or wall where possible.

Sun

A nest box exposed to the sun all day can be just as dangerous to young birds as a wet spring. Nest boxes are best positioned in an area that affords some shade from the hot sun. If your garden birds have a failure in a nest box that you think was due to overheating, think about changing the position the following year to a different location in the garden.  This doesn’t seem to have been an issue in my garden, as they flourished in last years hot weather.

Predation

There are lots of natural predators that could prey on your nesting boxes, but the most common are cats, magpies and squirrels.  Open-fronted boxes are particularly vulnerable to domestic cats if they are not carefully sited away from convenient cat perches. Even well sited boxes can be attacked by Great Spotted Woodpeckers using their ability to enlarge entrance holes in order to steal young birds. A metal plate surrounding the entrance hole can prevent this if local Woodpeckers have a previous history of attacking your boxes.

Natural Causes

Sometimes a nest failure may be related to inexperience of the parents, perhaps a very first breeding attempt by a young bird that doesn’t quite get the incubation or feeding regime right. Food supply of insects to feed young can be a major cause of nest failure. Our insect populations are clearly declining and many birds can find it difficult to gather enough insect food to feed a hungry brood.  You could try and help them out by featuring our Fledgling Mix in your feeders.

To end on a positive note, most birds will have the opportunity to breed several times over their lifespans and nest failures will for the most part be compensated for by broods raised the following year. Providing nest boxes improves a bird’s chances of success as most nest boxes offer a safer alternative to natural nest sites for the species that use them, even with the occasional failure they’re still a great way of helping our garden birds.

What Can I Do?

You can help to support fledglings and improve the chances of a successful brood by:

1. Feeding a suitable seed mix, such as our Fledgling Mix
2. Use a good quality nesting box
3. If you have a nesting box, consider adding a metal plate to keep predators out
4. Site your feeders away from the hot sun and out of particularly windy areas

***

Our Garden Birder’s Diary is written by Northumberland-based birder Alan Tilmouth who has been birdwatching for over 30 years and writing about birds in various guises for the last decade. A keen garden birdwatcher, he also manages to unearth the odd rare bird on his travels. You can find Alan on Twitter and his Facebook blog.