August at Oxwich: swallow roosts, passage migrants and a nocturnal visitor

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A dire start to August meant there was no ringing during the first two weeks of the month. Latterly, however, light to moderate easterly winds and open skies have predominated, and we have been able to make the most of the weather to complete both evening swallow / wagtail roosts and conventional morning sessions.

Species totals are below:

While there may well be one more session in August, the features of the catch to date have been:

  • Low numbers of garden warbler. We have missed the peak passage time in early to mid-August, and won’t get many more birds this year. September catches are few and far between, albeit we have once captured a bird in October.
  • Five grasshopper warblers, including four on 28 August, when both worn adults and freshly-plumaged juveniles were captured.
  • Fifty-four apparently healthy greenfinches (the species has declined significantly nationally due to trichomonosis), including one that had been ringed by Richard Dann in Southgate the previous year.
  • A total of 559 swallows. These were largely captured during three evening roosts sessions (peak catch of 269 birds on 24 August). Small numbers of sand martin (4) were captured coming in to roost with the swallows, while an opportunistic attempt to catch house martins on one of the evenings (when birds were among the swallows investigating the lure a couple of hours prior to dusk) proved moderately successful, with eight birds captured. An adult house martin was among those trapped (the vast majority captured are typically juveniles); the ratio of juvenile to adult swallows over the catches was approximately 18:1. A swallow initially ringed in 2019 was the only between-year recapture.
  • Two young marsh tits. While the species is common in the semi-natural deciduous woodland around the fringes of the marsh, it is relatively infrequent for birds to find the feeding station, and we ring them less than annually.
  • A nightjar. The first for the site and the highlight of the month. The species is common in suitable habitat in the north and east of the Gower recording area (in commercially-managed coniferous plantation in Neath Port Talbot in particular), but has been scarce on the Peninsula for many years following ceasing breeding on the commons in the 1970s / 80s. Rumours of renewed local breeding may be behind the capture; however, the marsh provides both sheltered and undisturbed day-roosting opportunities and excellent foraging, and is likely to be used by passage birds (as a couple of previous autumn sightings have suggested). Catching the species (it was a young female) was particularly gratifying, as it necessitated a very early start and a net ride had been trimmed out specifically for the purpose. We will continue to attempt to catch the species over the coming weeks, as birds have been seen well into September previously.
  • Five tree pipits. We took the usual bill depth and hind claw measurements to formally separate them from meadow pipit, but they are quite different birds in the hand, and this is a relative formality. As with garden warbler, we have missed a substantial proportion of the catching period of this sub-Saharan migrant, and are unlikely to get a particularly respectable total for the species in 2021 as a result. Passage will continue until approximately the second week of September based on previous data.
  • A sparrowhawk. A young female that became interested in the massing swallows and ended up in a net.
  • Our first wagtails of the year, with small numbers of pieds starting to roost in the marsh. Numbers build in September and October in a typical year. Grey wagtail passage has started, but we failed to catch any on 28 August, despite some reasonable effort; the marsh is currently very dry, and we did well in 2020 when heavy rain resulted in flash pooling in some of the rides.

We also heard back on a French-ringed reed warbler captured at Oxwich in late July. It had been ringed as a youngster at Tour aux Moutons, Donges, Loire-Atlantique, France in August 2020. Not remarkable in terms of location, but always nice to understand a little bit more about the various sites our birds are likely to rely on / visit over their lives.

It was good to welcome Cardiff University MSc student Georgia Arnold on 26 August. Georgia is researching micro plastics in birds and bats, and took faecal samples from 20 swallows away for further investigation. We await her results with interest.

Other wildlife recorded during the swallow ringing has included an oak bush cricket and a variety of moths attracted to the tilly lamp we use during evening roost sessions. The star among these was the Nationally Scarce B Webb’s wainscot (a species associated with fens and marshes with a restricted UK distribution) on 24 August. Other species have been brown china mark, small china mark, angleshades, rosy footman, dingy footman, antler moth and pinion-streaked snout. The young adder that favoured one of our reptile mats has not been seen for a couple of weeks, but grass snakes remain common beneath them.

Thanks to all those who attended sessions in mid to late August for their company and assistance: Heather Coats, Wayne Morris, Keith Vaughton, Colin Baker, Alex McCubbin, Amy Schwartz, Andrew Bevan, Bethan Dalton, Kate Hammond, Dan Jenkins-Jones, Dionne Jenkins, Ed O’Connor, Gareth Bowen-Llewelyn, Jo Conway, Miguel Lurgi, Richard Dann, Sarah Davies, Tom Wright, Val Wilson and Johannes Chambon.

Hopefully the settled weather will continue into September

Owain Gabb

28 August 2021

One of five grasshopper warbler captured in late August 2021
A young house martin, with broadly pale-tipped tertials
The young female sparrowhawk. Its feet left Keith’s hand looking like a colander
A sleepy looking nightjar. The first ringed on the marsh.


One of our two August marsh tits. Note the pale spot on the mandible
Adult (left) and juvenile (right) swallows. Although the extent of post juvenile moult recorded varied widely (with some youngsters having at least some metallic sheen on their heads), these two birds are relatively typical.
Webb’s wainscot. It makes up in rarity value for its slightly subdued looks!
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