Garden and woodland birds – winners, losers and invaders

We have a small city garden. When we moved in back in 2006, it was just a lawn with no borders. We decided to plant hedges using native berry-bearing shrubs to encourage the birds. We planted blackthorn, hawthorn and wild rose, and to increase the volume of winter berries, cotoneaster.

The centrepiece at the end of the garden is a bird feeder with a selection of seeds and fat balls. The aim was to attract three species in particular, lesser redpolls, siskins and if I was lucky, waxwings, plus the local blue tits and great tits and great-spotted woodpeckers. This, I thought, was my contribution to increasing local bird biodiversity and my pleasure in birdwatching.

Lesser redpolls were regular breeding finches in the city up to about 2000. Their song flight could be heard across the city from March to April. Then they suddenly disappeared. The last confirmed breeding was in Coleridge in 2002 and a male in display flight was seen over Carlton Way in 2014. Typically, they are birds of northern birch forests. Why they disappeared is uncertain but is possibly associated with global warming.

There might be a disconnection between a warming climate and the availability of insects to feed nestlings.

Siskins are uncommon but regular winter visitors feeding on alder and birch seeds, and waxwings are irruptive winter migrants arriving from Scandinavia about every five years (more about them later!)

Siskins visited the garden and so did a single waxwing in 2013 but no sign of lesser redpolls. In the meantime, blue, great, long-tailed and coals tits, robins, greenfinches and blackcaps in winter are daily regulars. This I thought must benefit our local breeding populations, but now I’m not so sure.

A recent talk by Jack Shutt, a researcher from University of Cambridge, to members of the Wildlife Trust showed that general bird feeding can exceed the local availability of food, causing an increase in dominant species such as blue tits, great tits and great-spotted woodpeckers. This may, however, have a negative effect on biodiversity.

Numbers of breeding blue tits, great tits and great-spotted woodpeckers have increased in British woodlands more than anywhere else in Europe.

This increase may have been partly responsible for the recent decline of three woodland species: marsh tits by 78 per cent , willow tits by 92 per cent and lesser-spotted woodpeckers by 73 per cent. Up to the mid-1980s, lesser-spotted woodpeckers were considered our commonest woodpecker in the city but are now reduced to just three possible breeding pairs in Cambridgeshire.

The local habitats of these three species have changed little over recent years and it is difficult to account for these population declines. Willow tits and lesser-spotted woodpeckers are hole-nesting species and may be out-competed for nest sites by blue tits, great tits and great-spotted woodpeckers. Non-native grey squirrels may also have a negative effect on our bird populations.

All this should be balanced against the immense enjoyment of connecting with nature and the pleasure of feeding garden birds by 17 million UK households, including me!

Annually, we provide 150,000 tonnes of garden bird feed and spend £250million on bird food.

If the berry crop fails in Scandinavia, bohemian waxwings arrive in the UK in winter in numbers. The most recent influxes were during the winters of 2012-13 and 2016-17, and this year is just such an invasion year. Flocks of up to 40-plus of this spectacular starling-sized bird have been seen in Coton, Great Shelford and in the city around Maids Causeway and Cherry Hinton, feeding mostly on rowan tree berries, especially those with pale, orange-coloured berries, mistletoe, and yew berries.

They can be evasive, one day there, the next day gone, one minute there for all to see, the next gone only to reappear some distance away.

They breed in the very northern sub-arctic pine forests of Scandinavia and Russia. Sometimes they eat semi-fermented berries which temporarily intoxicate the birds, making them incapable of flight but they recover quickly because of a very efficient liver. Better than us humans!