Sunday, 16 November 2014

How to help House Sparrows

House Sparrows are said to be in trouble in the UK. They are a red-listed species, apparently in a  worse predicament than Swifts which are only amber-listed, even though, according to official estimates, there is only 1 pair of Swifts for every 60 pairs of House Sparrows.

Although the rate of decline of House Sparrow numbers has reduced since 1994, the start of BBS, prior to that, between 1976 and 1994, there had been an enormous drop of about 70% detected by the Common Bird Census (see BTO webpage)The causes of the decline in House Sparrows are stated to be a decrease in survival and a decrease in productivity.

There is little data on the population level of Swifts prior to 1994, apart from the Atlases of 1968-72 and 1988-91, which show a contraction. It could also be the case that environmental factors affecting food availability are a contributory factor in the decline of Swifts.

A House Sparrow in an internal Swift box in Fulbourn
House Sparrows also largely depend upon cavities in human dwellings, but loss of nest sites has not been cited as a contributory cause of any decline. This is surprising, since modern building standards, renovation practices and insulation policies would affect House Sparrows at least as much as Swifts. 

This may be more damaging for House Sparrows, as they prefer to nest in close association with their congeners, whereas Swifts will nest either alone or in close association with each other, depending upon the distribution of cavities.

Many more House Sparrows than Swifts occupy these
Zeist boxes at Edgecombe flats, Cambridge
It is therefore good news for sparrows that they will happily occupy Swift boxes. It seems that a horizontally extending cavity, with an entrance near the floor, is perfectly acceptable to sparrows. 

Sparrow terraces, comprising 3 adjacent tit-like nest boxes are commonly erected for House Sparrows, but occupancy rates are low. They host more Great Tits and Blue Tits than House Sparrows.

Swift nest on top of House Sparrow nest at Ely Maltings
Should Swifts wish to take over a Swift nest box occupied by House Sparrows, then they will usually evict the sparrows, and then nest on top of the 'haystack' built by the sparrows. 

There can be a risk that Swifts get themselves entangled, especially if string or twine is brought into the nest, so removing this at the end of the season might be a good idea.

Therefore, if you wish to help House Sparrows, erect plenty of Swift boxes!