Pioneering ways to monitor bird movements, including their frustrations as well as achievements, featured at the 2020 Hertfordshire Bird Conference on Saturday 29 February.
A capacity audience at the Affinity Water offices in Hatfield, heard how a sound dish electronically capturing the calls of overflying night-time birds in a garden near the M25 has yielded records of unexpected species such as Black-necked Grebe, Common Scoter and Lapland Bunting as well as mass seasonal movements of Redwings and other thrushes.
Picture shows the conference speakers (l to r): Paul Roper, Graham Knight, Murray Orchard, Martin Ketcher, Bird Club Chair Rupert Evershed, David Darrell-Lambert and Carl Barrimore (© Tim Hill)
Enthusiast David Darrell-Lambert described how he became interested in the potential for nocturnal migration sound monitoring (known colloquially as 'noc-mig') to yield new insights into bird manoeuvres in the dark. His data gathered since 2016 suggested, for example, an October overnight movement of more than 900 Song Thrushes, when the maximum daytime count was around 200.
But he acknowledged drawbacks to the approach, ranging from its unsuitability for monitoring migratory birds such as Fieldfares that rarely call in night flight, to the time required to analyse overnight, real-time recordings. He was, however, hopeful that improving knowledge of night calls and smarter software that would help filter-out extraneous noise and simplify the interpretative task.
The conference, organised by the Herts Bird Club / HNHS and the British Trust for Ornithology (BTO), also heard from experienced bird ringer Paul Roper about a joint project established by the Herts & Middlesex Wildlife Trust, Lee Valley Regional Park and the Environment Agency to monitor Gadwall and Shoveller ducks with tracking devices. Efforts to trap Shovellers at Rye Meads were unsuccessful, but canon netting led to solar-charging transmitters being glued to the backs of four Gadwall, including what turned out to be a male-female pair.
Monitoring the birds' whereabouts every half-hour was abandoned because it ran-down the batteries too quickly, but useful information still was obtained by limiting data gathering to just four points a day. This showed that the birds' home ranges varied widely, with the paired ducks travelling as far as 20km to the Hatfield Forest. The transmitters fell off between 24 and 86 days later, with no evidence that they had prevented the ducks from feeding or behaving normally. Another interesting learning point was that the female Gadwall's transmitter re-charged more quickly than those of the three males – attributed to the males' longer scapular feathers restricting the amount of light reaching the solar panels.
The continuing importance of older monitoring methods was, meanwhile, highlighted by the BTO's Carl Barrimore who spoke about the Nest Record Scheme introduced more than 80 years ago. Unlike annual counts, such as the Breeding Birds Survey (BBS), the emphasis is on the timing and success of individual nests. Volunteer observers are asked to visit four or five times to record data on the laying dates, clutch size, brood size and fledging success.
Records are increasingly submitted online, and the data is used to produce a population index, indicative of how far change in a species population may be attributable to nest productivity. Other factors such seasonal temperatures and food availability are included in the analyses.
Graham Knight provided a review of Hertfordshire bird sightings for 2019, when a "pretty average" 193 species were recorded, compared with 192 the previous year. The highlights included a long-staying pair of Cattle Egrets in Cheshunt and seven records of Yellow-browed Warbler. No Nightingales were reported for first time since 2003 and only one Turtle Dove.
Herts BTO representatives Martin Ketcher and Murray Orchard gave an overview of current projects, including a new national survey of breeding waders in wet meadows. Volunteers are wanted to survey 26 county tetrads for the Breeding Birds Survey (BBS). They are also needed for five of the county's 10 Waterways Breeding Bird Survey (WBBS) sites.
Thanks, once again go to Alister Leggatt and Affinity Water for hosting the conference and providing refreshments. Reporting on water levels in Hertfordshire's chalk aquifers, Alister said the heavy winder rainfall had brought a major improvement – although levels had so far only returned to 'normal' after three years of drought.