Flies’ eggs on hatching Curlew eggs

Richard Tyler has taken some fascinating pictures of flies’ eggs on a hatching Curlew egg – not an occurrence that is widely noted in the literature.

He and others have been monitoring a Curlew’s nest on the Cotswolds in Gloucestershire – in itself a rare event, of which more below. The nest was on private land and the estate manager was extremely interested and supportive, erecting an electric fence around the nest as soon as it was found.

The eggs began to hatch in the last week of May. Richard reports: “On 30 May, two chicks were outside the enclosure and no birds were incubating. The nest showed two hatched eggs for sure and possibly part of a third. There was a chick calling and just starting to chip its way out of the fourth egg. We did notice a fly on the egg. On examining a photograph when I got home, I could see large numbers of fly eggs in and around the hole in the egg. We could only assume that the parents had given up on this egg and it hadn’t been incubated for some time, even though the chick was calling strongly from within. I have checked this morning and the chick is dead inside the egg. Both parents were in the field this morning, well away from the enclosure and closer to the river. They were acting very much like they had chicks!”

He adds: “Our number one concern is that because it has been so dry the grass crop is so poor and thin making the birds more visible. We also worry about them having access to water.”

David Scott-Langley, one of the most active insect specialists in the Gloucestershire Naturalists’ Society, comments “ The eggs are from one of the “blowfly” species of which there are a number and it is not possible to say which in this case. They lay their eggs on anything that has the slightest aroma of decay and from the picture some eggs have been laid inside the egg on the chick itself. If the chick has been struggling  for some time to extricate itself from the egg, then any deposits left in the egg may have started to decay and attracted the fly or flies. The chick being still damp will have added to the aroma. The fly eggs will not have been the cause of death. This is just a theory but seems likely to be the case”.

It would be interesting to know if there are other observations of flies’ eggs being laid on still viable eggs.

The nest was on the Cotswolds in Gloucestershire, an area where there must once have been large numbers of nesting Curlews, as mentioned in Ivor Gurney’s First World War poem ‘Crickley Hill’ – “where the Curlew ever and again cries faintly”. Since then changes in agricultural practice mean that only a few pairs of nesting Curlews survive there, and most Gloucestershire Curlews are now found in the floodplains of the Severn Vale. All of which means that any nesting Curlews on this higher ground of the Cotswolds are a very high conservation priority.

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