by Andy Wakelin
WE HAVE commented before in this column about the regular counts of birds on the Basin and how important it is to keep an eye on population trends. This vigilance is recorded in the publication of ‘The State of the UK’s Birds 2011’, available from the RSPB website.
This digest of all the bird population monitoring effort over the UK since the mid-1970s gives a good idea of what is happening to birds in general and we can compare the countrywide trends with our local figures.
The main local count is done for the Wetland Bird Survey (WeBS) and is carried out monthly by a skilled band of volunteers around the Basin and Duns Dish. This scheme aims to count all the wildfowl, waders and gulls at high tide on an appointed day and provide a picture of bird population on the Basin as well as adding to the data from around the UK. The figures for the Basin can be found on the montrosebasin.org.uk website.
The trends that are emerging from the masses of data collected over the past 35 years make interesting, if sometimes grim, reading. Interpreting this data is difficult and the reasons for the changes can only be explored by further research, so, at this stage, there can be only informed speculation.
What of our Basin birds? Well, the Shelduck is doing well on the Basin, with rising numbers over the last 10 years, but this is not the national trend where numbers are falling over that same period. So the Basin has something that the Shelduck like and now hosts 10 per cent of the Scottish population.
The Eider dusk is the iconic bird of the Basin, with around 300 nests in the summer and birds here all year round. The amorous ‘cooing’ of the males in search of a mate is heard over this holiday season as pair bonding takes place. Its fortunes have been pretty stable in Scotland as a whole and numbers have been increasing on the Basin, so, once again, a healthy picture at the moment.
However, it is not all good news. The Redshank, Dunlin and Curlew have all shown steady declines in the UK over the last 20 years and this trend in reflected in the Basin counts as well.
Three possible causes for these declines in birds on estuaries have been put forward in the State of UK Birds report. The first is range shifts. This is a possible response to global warming where birds move their normal breeding and feeding grounds to get the right climactic conditions and to follow their food sources, if they are moving for the same changes in climate.
The second is flyway populations. If the total number of a particular species of migratory bird is declining due to challenges anywhere along its migration route, then the picture in the UK is simply reflecting those changes.
Third is habitat quality. Estuaries are complex biological systems that involve the mixing of fresh water from rivers and salt water from the sea on a tidal rhythm that governs the productivity of the organisms on the mud. Pollutants from many sources can upset the balance and reduce the amount of food available to all the organisms that rely upon it.
The information provided by the long-term monitoring of the Basin’s birds gives us some confidence that the habitat is in good order as many birds are showing equal or better performance than the rest of Scotland. For instance, the Shelduck, mentioned earlier, rely on the supply of hundreds of thousands of spire-shell snails, called Hydrobia, and there are clearly plenty of them for the burgeoning Shelduck population, so the habitat would seem to be in good order at the moment.
The Redshank and Dunlin trends on the Basin are worse than the Scottish figures suggest, so there may be cause for concern over those species. The question is, what is changing about the Basin that is discouraging those birds? Again it would require some specific research to try to find out exactly what these waders need and whether the Basin habitat is at fault.
The reasons for all these problems are still unclear, but it is vital that every effort is made to keep the environment healthy and keep counting the birds. The canary was the coal miners’ early warning of trouble ahead and now we must rely on many other birds to give us the data we need to identify the problems as they happen.