14 October 2014

Technical wizardry helps monitor Merlins

For many of us who can’t enjoy this species on its breeding grounds in the moorlands and uplands, the Merlin (Falco columbarius) is a bird of autumn and winter when they can be spotted in the lower lands chasing Skylarks or other passerines. The BirdTrack graph below illustrates that pattern, with an obvious peak in October. An increase in sightings in October is potentially also due to the presence of passage migrants and the incoming winter population.

Merlin chart from BirdTrack
Recently, Roy Filleul, a birdwatcher and photographer from Jersey, captured images of a juvenile Merlin on the side of a pond. The following day we received a phone call from a member of the public reporting a Merlin that had been taken into care in the JSPCA (Jersey Society for Prevention of Cruelty to Animals). Unfortunately this was the same bird that had been photographed by Roy and, sadly, it didn’t survive due to injuries.

Merlin, by Roy Filleul
The bird in question was ringed in the nest last June in Lancashire, one of their strongholds (click here for top five counties for species in 2013). Although this Merlin didn’t travel a long distance or move in an unexpected direction, this is the first time one ringed in the UK has been found in the Channel Islands.

As you can see from the photograph, as well as being ringed, this bird was also PIT (Passive Integrated Transponder) tagged. These tags work in a similar way to Microchips for a dog or cat except that they are mounted externally (on a ring) rather than being inserted under the skin and are read by a receiver placed by the nest (by a licence holder). Metal ringing allows us to gather information on movements as well as survival; for example, it is possible to infer that when you stop catching a bird, that is normally caught year on year at a particular site, it has not survived (the principle behind the Retrapping Adults for Survival Scheme). As it is often very difficult to re-catch adult raptors, using a PIT tag allows us to follow a bird throughout its life to obtain data that categorically tells us the bird is still alive. If nests are monitored by a licensed nest recorder, levels of productivity over its lifetime can also be obtained from PIT tags. Unfortunately, as this bird died before returning to its breeding grounds, we will never know what information we might have gathered from this individual.

Currently in the online ringing database we have 54 recoveries of UK-ringed Merlins that have been found abroad, 35 of them in France. Also notable are the 31 Icelandic Merlins found in the British Isles, mostly recovered in Ireland. This reflects the fact that many British breeders winter on the continent and our remaining winter population is joined by winter visitors, predominantly from the Icelandic breeding population. See map of recoveries below.

Merlin recoveries map, from the online reports

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