The 2024 season began for BL on May 4th with a single male on a chilly evening at one of the GWT Reserves. This is a typical first date for the Forest.
Not so typical this season were changes in both personnel (see below) and to some extent, locations. Some of our long-term favourite Nightjar sites have dropped off our survey list, due to them outgrowing their suitability for the birds. Clearfell habitats have a certain lifespan during which Nightjars will use them. The length of time a clearfell is used changes according to when re-planting occurs and the rate of growth. We also believe it’s somewhat tied to the lifespan of individual male birds, in that site loyalty seems to take precedence over site suitability, and it will actually be the death of a particular bird that marks the end of Nightjar usage of a particular site. Much of this is hypothesis on our part. Nevertheless, this year has seen us retire a small cluster of sites in the west of the Dean, as well as a site very familiar
to mountain bikers in the north of the forest.
Conversely, we’ve added a series of new sites to our survey list as further forestry operations over the last couple of years have produced likely looking sites, at some of which we proved occupancy for the first time this season.
Site FF in the centre of the Forest was the early hotspot, with three males present on May 11th. All the early records were of males; they usually arrive around 10 days before the females and this pattern reflected in the first female record being from May 20th. While Site FF continued to have Nightjar present through the season, some of these birds must have dispersed, there were no detections from the AudioMoth recordings (see below) between the 19th and 29th June.
We met with OS and DS who had volunteered to assist in the monitoring work. They kindly agreed to deploy and collect some of the Audio Moth acoustic monitoring devices. The pre-season testing of these units was depressing; roughly half of the devices were not functioning. They had been carefully stored in the same circumstances as previously, batteries removed. We tried flashing the firmware and re-installing and in the end managed to field 12 functional devices. This reduced substantially the number of sites we were able to monitor remotely and simultaneously. We therefore concentrated on sites that we were less likely to visit in person. After the initial deployment, we selected a further 11 sites and did a second round.
Results from AudioMoths
Devices were deployed at 23 sites and configured to record from 2115 to 2300 and from 0300 to 0430, reflecting the crepuscular activity pattern of the birds. 5 of the 23 deployments resulted in no data being recorded, due to devices failing in some way. The remaining 18 deployments generated 345 usable files, with Nightjars detected in 140 (40%) of these. Nightjars were detected at least once at 10 of the 23 sites. There was churring detected at 5 sites simultaneously at 2147 on the evening of the 27th May, a smaller number than the previous year’s best simultaneous count of 11, the result of a more speculative set of sites being selected and deploying fewer devices.
At site F, 10 sessions from the first 5 days showed a male singing on all except one but then followed a period of 7 days with no detections. This was at the end of May and likely to be an unpaired bird that went to try his luck somewhere else. As in previous years, use of Audio Moths ‘found’ another new site, on a recently cleared area , only a single detection, but a good indicator that it’s likely to host birds in the next few seasons . At another site ( XYZ), data from the previous year, and a quick look at this season’s recordings that confirmed presence of birds, enabled location of a nest.
This was the first year in ten that we had no plans to undertake any ringing or tagging. The ringer MG who has made a huge contribution to our project, had indicated before the season that he wanted to focus his energy on the other end of the day with dawn ringing at his CES. Happily for us, another ringer, RH, has agreed to work with us, as we are keen to follow up on the GPS tagging that produced interesting results in 2023. More about him below. Despite our lack of ringing plans, all the young Nightjars at nests were ringed.
Nest Finding
More nests were located this year than any previously, as far as our project goes, but quite possible that this exceeds any previous county records. As ever, this part of the effort was led by BL, but with the significant addition of RH, an experienced nest-finder, who was interested in finding nest locations to assist with trapping in the following season. Additionally, some nests were found during work to locate Tree Pipit nests.
Site G was the next site to reveal Nightjar this year and would go on to be the most visited, and
searched, site this season. On most visits, two males were heard or seen. One pair of birds managed to completely elude us here, leaving us with no idea where/whether they may have bred. Another pair almost managed the same, with BL finding a trio of birds on or around fledging time.
Site CC was the site of BL’s first nest find this year. The male here was recorded churring in 2023, according to song analysis from both years. Last year, as far as we could tell, he was not paired and there was no evidence found of breeding. Having spent evenings watching a pair of birds BL was convinced he knew the location of the nest. Eventually, the nest was found in one of the most distant places from that location possible, on the other side of the reserve! This nest would go on to produce two chicks. A couple of weeks after hatching, when BL noticed that the male had taken over care of the young, he immediately went back to the other side of the reserve and went straight to the nest of the second brood which the female was now incubating. Were both nest sites prospected initially, or was the location of their first brood changed at the last minute?
Table of nests/outcomes
Overall numbers
We can report cautiously that the number of males appears to be stable, continuing a pattern over the last few years. There were observations at 18 sites, with breeding confirmed at 7. Roughly a third of all sites held more than one male.
We had more data about breeding success this year than ever, confirming our previous experience that nests are often predated. Is there recruitment to the FoD population from elsewhere that buffers the productivity rate of the birds nesting there?
Last field date was August 18th, at Site J, the day after two chicks were ringed there. This nest would have been started in the last week of July, following an earlier, failed attempt.
The highlight of the season was surely the number of nests located, surpassing all previous efforts. Other memorable encounters included a nest that afforded a really good view from a safe distance, without disturbance to the incubating bird, and a Nightjar twice being vigorously pursued by a bat, species unknown.
Looking ahead to next year, we have plans to work with GPS tags again, with a larger number of birds, and over a wider area, as we go international (well, a few miles over the border into Wales).
