Mute Swan Ringing in Christchurch Harbour
In response to some comment that appeared on the site around the time of the Mute Swan Upping in July, Ed Brett, the CHOG Ringing Secretary, gives us this article; which gives an informed insight to the purpose and objectives of the annual round-up.
Recently the CHOG web site has carried information and comment relating to the annual round-up of Mute Swans in the Harbour. There was implied criticism in the remarks, questioning the purpose and value of the exercise and deprecating the disturbance to wildlife and harbour users, particularly birdwatchers. Although the comments were declaredly personal, and do not represent CHOG policy, in order that a balanced picture is presented I have been invited to submit some background to the operation from my perspective as CHRS Ringing Secretary.
Swan ringing at Christchurch is organised and undertaken by members of the Swan Study Group, and has been for at least twenty years to my certain knowledge. The longevity of the species means that studies have to be carried out in the long-term. It enjoys the support of both Christchurch and Bournemouth Councils, through whose offices the operation is facilitated. It should be made clear that CHOG policy is to support scientific research in the Harbour area, and that the Mute Swan project has received much active assistance from members and friends of the group over the years.
The Mute Swan population is monitored as part of a detailed regional study encompassing the catchment areas of the Hampshire Avon and, to a lesser extent, the Stour. Other areas of the country have similar studies, so the local operations fit into a national framework. The studies depend to a large extent on the swans being individually marked, and hence the need to catch and ring them. It is worth noting that the term 'swan-upping' is somewhat misleading, since it traditionally refers to the ceremonial activities of the Liveried Companies on the River Thames. It is more usual to refer to a 'round-up' in the local context.
Mute Swans, in common with other large wildfowl, undergo an annual, simultaneous moult of their primary feathers. Until the new feathers have grown sufficiently, the birds are unable to fly. It is therefore convenient to attempt to catch them at this time. Christchurch Harbour is one of the few areas where moulting Mute Swans gather in large numbers and holds nationally important numbers during the summer months. By far the greatest proportion of the flock consists of non-breeding birds - failed breeders and juveniles as well as those adults that, for one reason or another, are not breeding that year. That said, the local pairs and their broods do sometimes get caught in the round-up. Much care is taken to maintain the integrity of the family group, and the cygnets and their parents are usually released first.
The technique for catching the birds in the Harbour is theoretically simple - you just have to surround them. This traditionally involves wading into position and then slowly walking towards a suitable landfall, although canoeists have become skilled at swan-herding in recent years. The swans move ahead of you, walk ashore, and are then corralled into sheep-pens erected for the purpose.
The amount and type of processing required for each individual swan varies. If already ringed, it is simply a matter of recording the details. New birds are fitted with two rings: a metal one bearing a unique number issued under the BTO Scheme; and a coloured 'darvic' engraved with alphanumeric characters relating to the specific study. Orange 'darvics' are used locally, other colours elsewhere - yellow and white for Weymouth and Abbotsbury for example. Birds are aged using plumage characteristics and, where possible, sexed. In some years, some birds have had blood samples taken for toxicological analysis. Any bird found to be fouled by fishing line or tackle is cleaned up.
The conspicuous nature of the Mute Swan results in the highest recovery rate of any species. They are often found dead and the ring details reported, together with the circumstances of their demise. The studies also benefit greatly from sightings of marked live birds, helping to document their movements and life histories.
Information deriving from studies such as this includes:
- mortality rates and how the factors affecting them vary with age;
- whether fidelity to moult sites varies with age and sex;
- rates of dispersal from moult sites;
- whether age at first breeding varies with population size;
- whether breeding density changes as the population grows;
- the movements of individuals both within and between river catchments.
On the subject of disturbance it is fair to say that the swans are subjected to a degree of handling that they would not normally encounter. However, it is a fundamental principle of studies of this kind that marked individuals behave in the same way as unmarked ones, in order for inferences and conclusions to be drawn. Another is that the welfare of the birds must always come first. Experience shows that after processing they walk and swim away, frequently begin to preen their feathers back into place, and carry on as though nothing had happened. As for other bird species, my impression is that the disturbance is minimal, similar in scale to that generated by the horses walking about. The round-up normally occurs at low states of tide when waders are more likely to be on the mud than on the Marsh. The area used for the corral is relatively small and there remain ample areas for wading birds to feed undisturbed, and for birders to watch them.
I hope that this brief account goes some way to explain the reasons behind the annual Harbour round-up.
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