15 August 2016

An unexpected but timely recovery

Gary Clewely (BTO) writes:

Nightingales are one of the best-known species in the UK for their impressive vocalisations, yet will be increasingly unfamiliar to many of us due to a marked range contraction and population decline in recent decades.

The motivation behind the BTO Nightingale tracking study is to identify key migratory routes and wintering areas to inform conservation. Fieldwork during the 2016 Spring was particularly exciting, because in addition to retrieving geolocators from previous years, this was the first time GPS loggers weighing less than 1 g were fitted to Nightingales in the UK, which if recovered the following year would give us unparalleled data on their migration.

Nightingale. Photo taken by John Spaull

During a mist-netting session at Alton Water (blue pin on map), in Suffolk (managed by Anglian Water, one of the tracking study partners) where we were catching males for tagging, one of the birds caught was already carrying a BTO metal ring – NA82699. This was initially not too unusual, especially as ringing was taking place on the site. The bird was swiftly processed and fitted with a GPS tag before being released safely back into its territory. Later, it came to light that NA82699 had in fact been ringed in January 2016 during an expedition to the Kartong Bird Observatory in The Gambia (orange pin on map). This is the first case of a Nightingale ringed in sub-Saharan Africa being found in the UK but remarkably, it is not the first exchange of Nightingales between East Anglia and the Kartong survey area. In 2011 and 2012, Nightingales ringed in East Anglia were recorded in Kartong, including a bird originally from a site near Ipswich, just 10 km from Alton Water.

Of course, recoveries in and from Africa are hugely dependent on effort and are biased depending on where ringing activities take place. Nonetheless, it is extremely encouraging that the ongoing monitoring at places such as the Kartong Bird Observatory is valuable and well placed to help inform us about migrant bird populations.

Olly Fox, who was on the January trip to The Gambia, reports that the Kartong ringing survey has a relatively high retrap rate for Nightingales with four birds encountered in multiple winters (in addition to the three exchanges between Kartong and the UK) from only 17 birds ringed between 201115. Olly goes on to tell me that wintering Nightingales in the coastal part of The Gambia are generally found in patches of dense vegetation but can also occupy secondary habitat, such as disused farmland. For males at least, these territories are defended throughout the winter months. However, increasingly these habitats are under pressure from development of agriculture and clearance of woodland and scrub to satisfy a rise in demand for firewood and charcoal. These are perfect examples of land-use changes occurring across the range of many migrant species that are important to identify and understand when considering their conservation.

Nightingale singing. Photo taken by Amy Lewis

Far from jumping the gun on the tracking study results, recoveries such as this complement tracking well, providing useful context and help to focus winter ringing efforts and inform local conservation, in this case by the Gambian Department of Parks and Wildlife Management and other NGOs. We will still need the detailed tracking information to understand the precise routes taken and the timing of their movements. The combination of continued tracking work and further ringing in The Gambia will help us understand how typical the apparent connectivity of Nightingales between East Anglia and coastal Gambia is.

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