89% of Blackbird nest failures are attributed to predators

A massive new study that has collected data from more than 2,300 blackbird nests over the past fifteen years shows that blackbird nest failures are directly linked to predation by magpies and other predators. 

This new study, published in an online supplement to the science journal IBIS was carried out by scientists from the Game & Wildlife Conservation Trust in collaboration with the University of Reading and aimed to investigate the links between predator numbers, habitat management and nest success in a common farmland songbird.

Dr Chris Stoate, Allerton Project Head of Research with the Game & Wildlife Conservation Trust explained, “Nesting is an important part of a bird’s life-cycle, and understanding what factors affect the success or failure of each nesting attempt could be important in our efforts to conserve songbirds on farmland. Predators are ultimately responsible for the vast majority of songbird nest failures, but we need to understand the combined effects that predator numbers, nesting habitat and their interaction have on nest success.”

Although blackbirds (Turdus merula) are not rare or endangered, they have suffered moderate national declines in recent years.  The fifteen year study took place on the Trust’s demonstration farm in Leicestershire during a period when a range of habitat improvements under agri-environment schemes were carried out as well as a predator control regime that formed part of a game management system.  The study combined nest and breeding population data for the species with data on abundances of two of its known nest predators, carrion crow and magpie. 

Blackbirds were chosen for this study because it is known that they can experience high levels of nest failure.  During the course of the study the researchers discovered that 89% of blackbird nest failures were attributable to nest predation by magpies and other predators.  Dr Stoate said, “A vulnerable time for nesting birds is early in the season, before the vegetation grows to conceal nests from predators.”

The research showed that nest survival was significantly higher for the period with predator control than the period without, at both the egg and the nestling stages.   However, an important additional finding was that, when densities of predators were high, the positioning of nests influenced their survival.  Chris Stoate explains, “These interactions suggest that when predator numbers are high, higher and more exposed nests have the lowest nest success.  Height and exposure are important in determining nest success.  Improved habitat or reduced predator numbers can influence the number of young birds produced”.

Patrick White, a PhD student with the University of Reading analysed the data and said, “When considering ways to improve the nest success of our songbirds, we cannot only consider effects of predator numbers or habitat alone, but must consider how the two interact.

“The control of nest predators may enable species like the blackbird to nest successfully in a wider range of nest sites within their territory, but any habitat management measures to improve nesting cover on farmland, such as management of hedgerows or scrub would also help improve nesting success. We are continuing our research on the specific effects of different agri-environment schemes and predator removal on a range of species and this will help to develop more effective conservation measures in the future.”

END

Photo:  black bird

Photocaption to read:  The Game & Wildlife Conservation Trust’s has collected data from more than 2,300 black bird nests over the past 15 years in an attempt to reduce nest failures caused by predators.

Picture credit: Peter Thompson, GWCT

Notes to editors

The Game & Wildlife Conservation Trust is an independent wildlife conservation charity which carries out scientific research into Britain’s game and wildlife. We advise farmers and landowners on improving wildlife habitats and we lobby for agricultural and conservation policies based on science. We employ 14 post-doctoral scientists and 50 other research staff with expertise in areas such as birds, insects, mammals, farming and statistics.  We undertake our own research as well as projects funded by contract and grant-aid from Government and private bodies.   The Trust is also responsible for a number of Government Biodiversity Action Plan species and is lead partner for grey partridge and joint lead partner for brown hare and black grouse.

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