New results from the British Trust for Ornithology’s (BTO’s) Garden BirdWatch suggest that the harsh winter could be having lasting effects on Britain’s smallest bird.

It’s not easy being a small bird, particularly during freezing weather. Weighing a mere 6g – less than ten pence piece – the Goldcrest appears to have suffered substantially this winter, occurring in 48% fewer British and Irish gardens from January–March 2010, compared with the long-term average (as calculated from 1995–2009). Although the decline was widespread, regional differences were apparent, with massive 60% losses in three corners of the UK: north Scotland, south west England and eastern England.

Goldcrests use gardens increasingly during winter as they feed on fat-based foods provided by householders. During severe winter weather a greater proportion of the overall Goldcrest population would be expected to use gardens, so the substantial decline in BTO Garden BirdWatch observations suggests a crash in the population at large.

Other small birds also declined. As winter mellowed into spring, the rich trill of the tiny Wren was absent from numerous gardens, with a 22% decline compared with the long-term average. The similarly diminutive Treecreeper, which scuttles up tree trunks in search of invertebrate food, was recorded in 15% fewer gardens from January–March 2010.

Dr Tim Harrison, BTO Garden BirdWatch, commented “The Goldcrest is a ‘boom and bust’ species – after cold winters only a quarter of the autumn population may be left to breed, but numbers can rally with pairs sometimes rearing more than 15 chicks in the following spring and summer. It remains to be seen how the population will shape up after the current breeding season.”

He added “Through their participation in the year-round survey, BTO Garden BirdWatchers, with their weekly reports, have provided an early warning of possible large-scale declines in the Goldcrest – something that the BTO is investigating currently.”