Secret Lives of Garden Birds

By Dominic Couzens - 17 April.

This was a wonderful lecture based on the ecology of our garden birds, full of facts that ranged from interesting to amazing to totally unbelievable. Dominic followed the seasons, showing how birds have developed hugely varied behaviour that enables them to survive, find food and breed successfully - and then start all over again. Facts came thick and fast, interspersed with jokes and sometimes it was difficult to separate fact from fiction – we had to be reminded that it was a joke when he showed us a slide of long tailed tit and said it had a retractable tail so it fitted into its nest!

Dominic started in autumn with ‘the moult’. Totally renewing feathers may seem wasteful, but it means that after the stress of breeding, birds can start again with plumage in tip-top condition. It also enables individual birds to change from juvenile to adult to full breeding plumage. This ability to change image affects how other birds respond to an individual and plays an important part in ensuring successful breeding behaviour. It can also affect social hierarchies as in robins where the young have no red breast and therefore avoid being attacked by adults.

In winter the problem of the unavailability of food is compounded by the short days (and long nights) that give substantially less time to eat. Birds have evolved a multitude of different ways to survive. Many just move country, requiring a huge energy drive and lots of food before they go. Our chiffchaffs may go to Spain, which sounds far enough, but what about the house martins going to Africa? And we still don’t know where in Africa; one of the bird world’s remaining mysteries. Migration is not, of course, all birds leaving our country. There is a net gain with birds coming to over-winter in Britain; migration apparently enables waxwings to subsist entirely on berries – the only European bird to do this.

Another way of solving the problem is to hoard food before the lean periods. The jay (garrulus glandarius) spends up to 12 hours a day collecting acorns – up to 5000 of them - which it squirrels (or scatter hoards) away. Forgotten we might think, but studies on different birds have shown that up to 80% of food stored may be found by them remembering specific landmarks. The jay’s collecting behaviour varies with the availability of acorns. Where there are oak trees within a jay’s territory it may carry 3 acorns at a time to its hoard. If no oak trees are nearby a jay may travel up to 4 km to find them and can carry up to 9 at a time, thus using extra energy in the carrying while economising on journeys.

For those birds that survive winter, in whatever way, spring comes, days lengthen and hormones change. Testes in the house sparrow may increase by 300 times their winter weight, and ovaries by 1000. When you’re a bird it obviously pays to jettison the extra weight during the non- breeding season.

Spring is synonymous with bird song and the dawn chorus; the beauty of it makes my jaw drop every year – but to a bird, song is more than just a pretty sound. To a female trying to choose the best mate available she can learn much about the age, experience and health of a male. A singing blackcap gives information about the density of the vegetation; a willow warbler warbles faster the more food there is available.

Mating behaviour and breeding systems are so variable and fascinating that I could fill the whole newsletter. The interest of the males and females conflicts: it’s in the females’ interest to have as many mates as possible to help feed the young, while it’s in the males’ interest to have as many females as possible to produce more chicks. This results in multiple breeding systems, monogamy, polyandry and polygyny – and they are all found in dunnocks. The type of breeding varies with the environment – and is endlessly complicated!

I’ve been trying to squash as many facts as possible into this short report, but there’s no room for more, only to ponder the fact that it is not surprising that such a wealth of different bird behaviour has evolved when one considers the problems involved in their survival. I shall finish, as did the lecture, with that well known ‘feel-good-factor’ - a sunset. And as an extra bonus, and to make us feel even better - a robin!

Penny Avant