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Songbird Science

Songbirds and science

The following blog is based partly on the witness statement from Wild Justice (passages in red) which was part of the claim issued to the court on 21 March (and emailed to Natural England although they will not have had a formal sealed document for some time after that due to court delays, but they had this in their email inboxes). The passages not shown in red were not part of the Wild Justice witness statement.

Carrion Crow. Photo: Tim Melling

The scientific evidence from large-scale and exhaustive studies does not support the idea that Magpies, Jackdaws, Jays or Carrion Crows have an impact on songbird numbers. For example the scientific non-governmental organization the British Trust for Ornithology states on its website about Magpies (my emphasis);

For many people the Magpie is a villain, responsible for the widespread decline of songbirds. Research examining the question of whether Magpies have been responsible for songbird decline has failed to find any evidence to support the notion that they are to blame. It is true that while Magpie numbers have tended to increase, those of many of our songbird species have declined. These increases and decreases have occurred over different time periods and in different parts of the country, which suggests that the general patterns are a coincidence and not cause-and-effect.

https://www.bto.org/volunteer-surveys/gbw/gardens-wildlife/garden-birds/a-z-garden-birds/magpie

… and about Carrion Crows;

Carrion Crows are opportunist feeders and have a wide and varied diet. Because they may take gamebird eggs and chicks they have been targeted by gamekeepers. Similarly, sheep farmers sometimes control thse (sic) crows because of the perception that they kill young lambs. However, insects and other invertebrates are the main prey in summer, with carrion and other scavenged food an important addition during the breeding season. Grain becomes important in the autumn and winter. The predation of eggs and young chicks tends to be highly seasonal, with the crows seeking to satisfy the needs of their own growing brood. Since these crows only produce a single brood of chicks each year, their impact as predators is restricted.

https://www.bto.org/volunteer-surveys/gbw/gardens-wildlife/garden-birds/a-z-garden-birds/carrion-crow

… and about Jays;

The Jay’s diet is actually more varied than this. Carrion is readily eaten and road casualties may be taken where a road runs through woodland. In the summer, the eggs and young of other birds may be taken as a source of high protein nourishment for their own chicks.

… and about Jackdaws, nothing at all about any suspicion that they are a cause of songbird decline . 

This is hardly surprising since BTO studies of long-term and voluminous datasets have not unearthed evidence for Carrion Crows, Jays, Magpies or Jackdaws having any impact whatsoever on songbird numbers. A significant paper was published in March 2010 by BTO scientists and co-workers from academic institutions (see here for layperson’s summary ) where the authors state;

In the biggest ever analysis of songbirds and their predators, published today in the Journal of Applied Ecology, scientists look at the role of predators in the decline of species such as Bullfinch and Yellowhammer. Whilst a small number of associations may suggest significant negative effects between predator and prey species, for the majority of the songbird species examined there is no evidence that increases in common avian predators or Grey Squirrels are associated with large-scale population declines.’ and also ‘There were a large number of positive associations between predators and prey, suggesting that predator numbers have largely increased as the amount of prey has increased. This is particularly the case for native avian nest predators (Great Spotted Woodpecker, Magpie, Jay and Carrion Crow). Although this largely exonerates these predators, as driving declines in the numbers of songbird species at a national level, it does not preclude individual predators having local effects. 

https://www.bto.org/news-events/press-releases/are-predators-blame-songbird-declines

The mass casual killing of such species as Jay, Carrion Crow and Magpie previously tolerated under the General Licences (now withdrawn after Wild Justice’s legal challenge – ‘ Marian Spain, interim CEO of Natural England, ‘the licences were unlawful’) does not appear to have any scientific basis in being useful for populations of songbirds.

In contrast there is evidence that some ground-nesting birds such as Grey Partridge and breeding waders can be more seriously affected by predation by Carrion Crows – though not to my knowledge by predation by Magpies, Jackdaws or Jays.

No doubt Natural England is carefully considering these matters when it comes to replacing the General Licences and no doubt the Chief Executive of the BTO, Andy Clements, who is also a Natural England Board member and Chair of the Natural England Scientific Advisory Committee, has been pointing out these studies, if Teresa Dent of the GWCT, also a Board member of Natural England, did not get there first with this science.

Jay. Photo: Tim Melling

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