2023 Season Summary

Our season started on May 7th, when BL visited sites G and AA and found singing males at both. May 10th is the average first report date for Gloucestershire, over the last twenty years. The same evening we were hearing reports from two other heath sites.

Two weeks later, we were back at site G for a catching attempt. We had two GPS tags, a new venture for us, which we hoped might provide some picture of where, beyond their home range, the birds may get to when foraging.  The previous year, we had an anecdotal report of Nightjar feeding at a farm around 6km from the northern end of the Forest. This is not an area with any obvious suitable breeding habitat, so we wondered if these were Forest birds.

Three catching attempts later, we were no further forward with this plan and BL’s extensive nest searching at the site had produced no results. Further searching later in June was similarly unsuccessful, though did yield some roosting males.

Meanwhile, from May 23rd, we deployed the AudioMoth recorders, concentrating on known sites, rather than speculative new clearfells. Once again we configured these to record at both dusk and dawn. 15 devices were used and 13 were successful in producing a set of files. Of these, Nightjar were recorded on at least one occasion at all sites. In the pre-dawn period of May 27th, male Nightjars were detected churring simultaneously at 11 sites.  

Recent and extensive new felling at site J was already occupied. This is an example of potential Nightjar habitat being created, not as a result of heathland recreation or routine timber harvesting but from disease control. Larches are being felled to control Phytophthora Ramorum, which can affect several tree species, but in the British Isles affects predominantly Larch.

At site FF, where a male has been detected for the last three years, when we called there one evening to collect the recorder, we found two males singing and at least one female present. This site has also had some additional felling, increasing the amount of open ground, and the area is being allowed to become wet again. It will be interesting to see how long it remains attractive to Nightjar.

Late in the season we left a recorder at a fairly new clearfell, where we have yet to spend an evening. There was a single detection over 7 days, but this is another indication of how valuable the audio monitoring is, in terms of discovering new sites.

There’s an AudioMoth recording device hidden somewhere here!

When all the AudioMoth recordings were examined, we found that a bird at site U sang continuously for 34 minutes, on June 4th, comfortably exceeding an 18 minute burst we recorded at another site in 2022.

After the unsuccessful catching attempts, we were starting to wonder if we would be unsuccessful in deploying our GPS tags. However, through a contact we heard that a nest had been located on a heathland site. We were able to see the sitting female from a sufficient distance to avoid disturbance.

The nest finder knew the rough laying date, and once the relevant permissions had been obtained and licenses were in place, the chicks were ringed. This was at dusk and a mist net was then put up near the nest, and the adults trapped. The female initially looked to be a re-trap, as she was already carrying a ring. However, it was not a ring that had been issued to the ringer in our team. This was the first time we had caught a bird ringed by another ringer – more about this later on.

The female was fitted with two tags, a GPS tag and a simple radio tag. These were mounted with water soluble string. The purpose of the radio tag was to enable the GPS tag to be located, once the string had dissolved and they had fallen off.

The fitted GPS tag with radio transmitter.

After an anxious couple of days, during which the female was not seen at the nest, it was evident that the male was attending the nest and the chicks continued to thrive. The female however, could not be located on return visits, until a more systematic search eventually turned up a signal. Narrowing this down took us to the female, now incubating a second clutch, about 225m away from the first nest.

A few days later, we checked the nest and installed a trailcam and audio recording device. We also recovered the GPS tag, rain having dissolved the string; it was on the ground in the vicinity of the nest.

Miniature Nightjars!

Connecting the tag to the PC interface showed that the tag had recorded a series of data points. From this a KML file is produced which, when opened in a viewer, for example Google Earth, the resulting plot showed the female’s movements over the last week. Three things in particular stood out.

Firstly, the amount of fixes, not only in the vicinity of the nest, which was to be expected, but also the rest of the territory, were almost entirely restricted to the reserve, suggesting that she was able largely to meet her feeding requirements there.

Secondly, there were a few visits to the neighbouring heath, where there were two males, one of which we believe to have been unpaired throughout the season. The fixes were in the vicinity that he regularly sang from. Nightjars are known to mate switch for second broods, allowing us to speculate about the paternity of the chicks in the second nest.

Thirdly, there were a few flights to a farm on the banks of the River Severn, a couple of kilometres or so away. From the satellite view, this looks to be an arable farm. We have yet to visit, but wonder if the location where the fixes were registered – around some farm buildings – perhaps has a bright security light that attracts moths.

July was relentlessly wet, rain fell on a majority of days after the second clutch was laid until hatching, but the female sat tight. On our last visit to the site, the trailcam was retrieved, and the later images showed the chicks looking like miniature Nightjars, ready to join the fledged birds from the first nest in learning to forage.

Information about the ring on the female showed she had been ringed 6km away, across the Wye in Monmouthshire. She had been ringed as a chick the previous year. She had thus successfully produced two broods in her first breeding season, despite the poor July weather. In addition to the data from the tag, her history is also of interest, in terms of post breeding dispersal and recruitment to the Forest of Dean breeding population, suggesting perhaps that the birds on this side of the Forest have more in common with the South Wales population than the main part of the Dean.

We can account for around 20 males in total, and can assume that there will be a few that we don’t know about. Although we have relatively few records of confirmed breeding this season, the population appears stable.