I came across this paper partly because it cites a paper I co-authored on Roseate Tern conservation many, many years ago. And the Roseate Tern is a species very close to my heart (see Fighting for Birds Chapter 3, In the pink – roseate terns). It’s a fascinating study which unlocks some of the facts that we pondered over and wondered about back in the late 1980s.
Roseate Terns go to the seas of West Africa in our winter and they, like many other terns, were trapped there by coastal human communities. Although Roseate Terns are rare terns, and therefore make up a small proportion of all the terns along the coast (Sandwich, Common and Black in particular, but other species too) they seemed to be particularly vulnerable to trapping and it probably was the case that this trapping was a factor in the decline of the species on its European breeding grounds.
By the way, the trapping was less subsistence trapping for food and more commonly little boys at a loose end.
But most of the ringing recoveries of Roseate Terns in West Africa, and indeed most of the sightings in Ghana were in the early part of the ‘winter’ – October-December – with a dearth of records after Christmas. This made sense because it coincided with the main season of the coastal fishery which depended on small fish that were just the species that the terns fed upon, and this further made sense because there was an upwelling current at around that time of year which brought nutrients to the upper waters of the sea and caused a bloom of plankton and a rise in fish numbers. But where did the terns go after Christmas?
This study used geolocators, put on Roseate Terns at two colonies I know well, Rockabill in Ireland and Coquet Island in Northumberland (I always try to glimpse it if on a London-Edinburgh train). Geolocators record where the bird is (daily at least) but have to be retrieved from the bird for their information to be accessed – they collect loads of data but don’t transmit it (so you need a species that survives and can fairly reliably be recaptured).
This paper confiirms that Roseate Terns go to where we thought they went (unsurprising – I, and others, have seen them there!) but it reveals loads of information. Where do the terns go after Christmas or in late autumn? It seems that some start moving back along the West African coast towards us but many stay in the same places. The results show that a lot of the time is spent far offshore – certainly way out of sight of land, and so the large flocks of terns I’ve seen on salt flats west of Accra, and at places all along the coast of Ghana, are only a small part of a much larger population. It’s facinating and I’ll spend more time looking at the paper.
As with all migratory species, there is a need to ensure the protection of food supplies and habitat throughout the annual range if the species is going to prosper.
But this is yet another in a long line of studies using geolocators which demonstrate how much valuable information can be collected through their use. Is it the end of ringing? Certainly not. Have we passed peak ringing? Quite possibly.