Using science to help a duck in trouble

Guest blog by Dr. Mark Hancock Senior Conservation Scientist at the RSPB Centre for Conservation Science 

Scottish lochs and their scoters

Complementing the majestic hills of the Scottish Highlands are its myriad lochs (lakes), ranging from huge lochs several miles long, running along broad glaciated valleys, to masses of tiny pools and lochans (mini-lakes), covering the surface of rolling peat bogs. Each summer a few of these lochs are favoured by nesting common scoters - large but shy diving ducks famous for their beautiful courtship displays.

A pair of scoters in relaxed mood at RSPB Forsinard Flows reserve in the northern Highlands and (inset) one of the iconic ducklings (photos: Andy Hay, RSPB)

Over the last few years I've been fortunate to have been given the chance to get to know this bird and its remote and magnificent breeding grounds, along with colleagues from RSPB, the Wildfowl & Wetlands Trust, Scottish Natural Heritage and The Conservation Volunteers. We're keen to work out how we can help this species, once so characteristic of the area, but recently much declined.

Why do scoters nest where they do? If we could answer this question, maybe we could use the information to help them recolonise their former haunts. So we designed a research study which compared lochs that scoters use, to other lochs that scoters have been abandoned: what's the difference?

What do scoters look for in a loch? 

Over three years, we made nearly 1000 visits to lochs across the Highlands, looking for scoters, and measuring the things they might be looking for when they choose their breeding sites. Maybe scoters prefer the lochs with the most food - aquatic insects like caddisflies and mayflies, and other invertebrates, like freshwater shrimps. Perhaps they need lochs where insect life is easiest to catch - with shallower water or softer sediments. Or might the preferred lochs be the ones with the fewest predators? For example, American mink, not native to Scotland, are starting to colonise the Highlands, and they often prey on waterbirds.

One of the field teams at a loch in the Flow Country during the three year scoter study. (L-R: David Bavin, Helen Jones, Mark Hancock; photo: Martin Clift).

Sampling insects for food availability 

Over the course of the study, nearly 50,000 individual freshwater insects and other invertebrates were sampled, counted, identified and measured. This allowed us to work out how much food was available for scoters at different lochs. We also measured loch depths and sediment types, and scoter use. Some lochs had scoters on nearly every visit, whereas others, formerly used by scoters, had no records during the entire study. Then we went back to base and analysed all the data: which of these characteristics tells you that a loch will be scoter-friendly?

Sampling loch insect life with a sediment grab (photo: Andy Hay, RSPB)

Large invertebrates & shallow water - a scoter's favourite loch

After years of fieldwork and months of data analysis, the study has been completed, and the results published here in the journal Aquatic Conservation: Marine and Freshwater Ecosystems. So, what have we learnt? Of all the different factors investigated, two come out clearly as being linked to scoter presence: large invertebrates, and shallow water. Of all the lochs we looked at, scoters bred most often at those lochs with the shallowest water and the most large, freshwater invertebrates. What's more, there was more freshwater insect life where there were fewer small brown trout - perhaps at some lochs, the fish were eating most of the scoter food?

Using research to help scoter conservation

We're now using these results to help design ways of helping scoters. For example, at hydro lochs, where water levels are to some extent under human control, could we aim to maximise the area of shallow water? In the north Highlands, where brown trout angling has declined in some areas, could we encourage more trout angling at certain lochs, and by reducing trout numbers, increase freshwater insect life? In the next phase of the work we will be working closely with those who use and manage these lochs, to see if we can together develop conservation measures. Let's hope we can keep the Scottish breeding population of this lovely bird, at our Highland lochs and lochans.