Birds

Blue tits are missing in our gardens after the spring heatwave

The lockdown has allowed many people to reconnect with nature, but evidence from the British Trust for Ornithology’s (BTO) Garden BirdWatch poll showed that some of our favorite garden species, like the blue tit, may have had problems this year due to the unusually warm spring.

For the past 25 years, the BTO has asked Garden Birdwatch survey participants to submit their records of garden birds in order to understand how these species are doing. This information has enabled us to see how even the most common birds can vary from year to year.

Blue tits have been seen in fewer gardens and in fewer numbers since May 2020. It is believed that this year’s spring, with the fifth warmest April in over 100 years, caused invertebrates, including butterflies and moths, to start early. Caterpillars are an important food for Blue Tit nestlings, but caterpillars develop early in warm springs and fewer caterpillars are available during the main Blue Tit nesting season, often resulting in decreased nestling survival and smaller populations overall.

Blue tits have been seen in 5% fewer gardens this August, with only 80% of gardens reporting these colorful birds when we would normally expect to see around 85% of them. If a similar trend is seen across all habitats, it could mean the UK is entering winter with over half a million fewer blue tits than a typical year. While this gap had closed somewhat by October, they are still being recorded in fewer gardens than is typical for fall.

Blue Tit, Copyright Glyn Sellors, from the Surfbirds Galleries

Blue tits are one of the most common garden birds that are reported in around 94% of gardens during the winter months and can often be seen in garden birdhouses. You are also one of the most common users of nest boxes. They can be easily distinguished from other garden birds due to their small size and bright blue and yellow coloring. We are very keen to see how blue tits develop in the gardens for the rest of 2020 and through 2021. A bad breeding season often means that the remaining birds are more likely to survive in winter as there is less competition for resources. That is, the population is correcting itself, but we need to keep monitoring the numbers to find out.

Another common garden species, great tits, have also been seen in fewer gardens and have likely been affected by the availability of caterpillars as well. Great tits have several similarities in common with blue tits, both of which are common in gardens and use garden nesting boxes.

We also recorded fewer other insectivorous species over the same period. Wagtails and wrens may also have problems due to the potential for lack of caterpillar forage due to early spring. For both species, reporting rates fell below average after June, when young birds normally appeared.

Not all species had a terrible year. Long-tailed tits, a small, black-and-gray bird with a long “lollipop” tail, had a higher than usual reporting rate from May, suggesting that these adorable garden birds had a successful breeding season.

BTO Garden BirdWatch saw a sharp surge in attendance during the lockdown in March and April as the program went vacant to meet a growing interest in garden wildlife as many people had more time to enjoy their garden birds.

Robert Jaques, Development Officer for Garden BirdWatch Supporters at BTO, says: “Thanks to the records submitted by our dedicated Garden BirdWatchers, we can see the effects of weather events on garden birds. We’ll be watching closely over the coming months how blue tits and other garden species deal with the coming winter. “

BTO’s Garden BirdWatch is a weekly wildlife survey that has been conducted with 20,000 active members for the past 25 years. Through the survey, BTO scientists were able to observe the changing fortunes of wild animals in the garden and thus understand how gardens can be made friendlier and more beneficial for wild animals.

Further information can be found at www.bto.org/gbw

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