Crumbly curlew eggs may pose another threat to species, say UK scientists | Birds

A scientist has started a national investigation into curlews, after noticing in a small-scale study that some of the eggs being laid by the endangered birds were unusually fragile and crumbly.

If it emerges that the problem is widespread, the fragile eggs could pose a grave risk to the future of the species, which has declined significantly in Scotland, England and Wales and by 42% between 1995 and 2008 in the UK overall.

Dr Nicola Hemmings, a researcher in the school of biosciences at the University of Sheffield, started working with the Curlew Recovery Partnership (CRP) conservation group last year.

She said: “I looked at a very small number of eggs because the CRP thought there might be some fertility issues. All of them were fertilised and showed some sign of embryo development but at least half of them had flaky, brittle or crumbly thin fragile shells. We have this hint there could be a problem here. It’s worth noting that those eggs with particularly thin shells had embryos that died in particularly late development.”

This finding worried her, so she asked the partnership to get samples from across the UK to see if it was widespread and whether there was any pattern with regard to egg quality and hatching success.

Nest monitors have been asked to send failed eggs and egg fragments to Hemmings, who will be analysing them to find out why they are becoming so crumbly. “We want to assess what degree this is a threat to the recovery of the curlew,” she said, adding: “The first step is to find out if this issue is widespread, then the next step will be to try to identify what the problem is, so what’s causing the problem with these eggshells. We will analyse eggshell samples to look for environmental contaminants that might be leading to poor eggshell quality and also look for evidence of poor nutrition.”

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If researchers are able to identify a problem, conservation teams could work with landowners in the area to reduce the pollution near curlew sites, or help the birds that are not finding enough food.

If the issue is inbreeding because of the constricted population, rather than something that is easier to fix, such as environmental pollution, the outlook would be poor. However, there are hopes inbreeding may not be the problem.

Hemmings said: “The one thing that did seem quite hopeful from our analysis last year was that the fertility issue didn’t seem to be a massive problem. These eggs were fertilised, which is the first thing people think of with respect to genetic or inbreeding problems. Doing this kind of UK-wide assessment will help us identify whether there are any problems with particular pockets and if there are any fertility issues arising.”

It is important that members of the public do not disturb nest sites, but conservationists involved in the study have been asked to keep an eye out for failed eggs, which they need to get into a fridge before sending them for analysis. They have also been asked for larger fragments from hatched eggs, to enable analysis of shell thickness at a range of locations.

The loss of the curlew has been most dramatic in the lowlands, and it is estimated there are most 300 pairs below Birmingham . It is thought these birds could die out in eight years if nothing changes. The curlew was added to the UK red list in 2015.

Prof Russell Wynn, who runs the CRP, said: “The UK and Ireland holds a quarter of the world’s breeding curlews, mostly concentrated in upland areas of northern England and Scotland. However, after dramatic declines in recent decades, they are now at real risk of extinction as a breeding bird across Ireland, Wales, and much of lowland England.

“In these areas we are seeing existing populations becoming increasingly isolated, and a lack of breeding success means there is a risk that they are now dominated by ageing and potentially infertile birds. This new research project will therefore inform conservation efforts in these areas by identifying causes of egg failure, and potentially also alerting us to impacts of chemical pollutants and/or poor nutrition on curlew breeding and wintering grounds.

“There was a recent study that basically showed the biggest kind of block for population recovery in the curlew is the early reproductive stages – the hatching and successful survival of young chicks. Every egg is crucial and every clutch is crucial.”

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