Nightjars on Thorne and Hatfield Moors – a talk by Lucy Mitchell, University of Hull
On Wednesday 5th February the Nats had a very interesting talk by Lucy Mitchell about the nightjars on Thorne and Hatfield Moors. Lucy had been studying the nightjars between 2015 and 2019 in order to gain her doctorate degree. Lucy began by telling us a bit about the nightjar’s behavior and about the habitat. She explained that nightjars are migratory and nocturnal and that the moors are not typical of where nightjars are usually found. In other parts of the UK nightjars are found in dry, sandy places and recently felled conifer plantations. Her role was to monitor the nightjars by using GPS tagging, to see how they are affected by the habitat restoration that is currently underway at both sites. The main habitat change that seems to have benefited the nightjars is the cutting down of swathes of birch trees. The nightjars can find their prey more easily (mostly moths and some beetles) by flying unimpeded in these clearings. The nightjars rarely fly over the stretches of water. The nightjars have huge eyes and are entirely visual predators.
Lucy tagged a total of 113 birds over the period of study and estimates that there are at least 20+ breeding pairs on each site, probably more because she was unable to study the whole area. She found that there were more males than females so there were a number of unpaired male birds. In order to retrieve the GPS data the birds had to be re-trapped and by the end of the study she had a 70% re-trap rate. I was interested to hear about one unattached male who decided to leave the moors for a week in the middle of the breeding season. When he returned Lucy was astonished to find from his GPS tracker that he had first flown to the Cambridge area, then had flown around Norfolk , back to Cambridge, then to Luton, to Wolverhampton, then to Birmingham airport then finally back to Doncaster. A total of 1,500 Km. However, the birds mainly stayed within the area of the moors with only a few birds wondering out to forage. This may indicate that the moors are an excellent habitat for them with plenty of food. She found that birds had smaller home ranges in cleared areas than in areas near open water, probably due to less suitable foraging. Three birds with repeated GPS readings all returned to the same home range. Lucy also found out that the Hatfield nightjars were more widely ranging than the Thorne nightjars. The Thorne nightjars seemed to like the old mining site, which is now a solar farm. 5-7 Km was the usual flying distance. Lucy described Packards Heath on Hatfield Moor as the best spot to see nightjars as it is a good breeding area and birds are often seen there foraging at dusk.
The Tags are the size of a 20p piece and weigh 1.7g; they are tied to the central 2 tail feathers with dental floss and record the GPS every five minutes and are accurate to 5-10 metres. The downside is that the tags cost a staggering £400 each.
Lucy spent last year in a laboratory at Sheffield University metabarcoding faecal pellets to discover what the nightjars were feeding on. DNA bar-coding is a method of species identification using a short section of DNA from a specific gene or genes. Lucy found that there was little information on the DNA of UK moths so she had to do this herself; catching moths in a moth trap, identifying them then killing them to analyse their DNA. Lucy found that a large percentage of the prey were the larger moths in particular Large Yellow Underwing, Silver Y, Poplar Hawkmoth, True Lovers Knot and Smoky Wainscot. The nightjars were therefore feeding efficiently by choosing the larger moths, hardly bothering at all with the smaller moth species.
Lucy finished her fascinating talk by telling us a bit about what she is working on now. She is working on the MOTUS system that uses radio telemetry and static receivers. The system is international, uses cheaper tags and involves less field work as the receivers are permanently set up. It is hoped to expand the system across the UK.
There were 23 members in attendance for the talk