Print page

Causes of common scoter decline

Flock of common scoters sleeping

Flock of common scoters sleeping

The breeding population of common scoter in the British Isles has been in decline for many years; most recently, this population halved between 1995 and 2007.  Reasons for these declines are poorly understood, but need to be reversed, or we risk losing common scoter as a British breeding species.

Project objectives

  • We aim to identify key features of lakes that are preferred by breeding common scoters in Britain, and use this information to develop and test potential conservation approaches that might help reverse population declines.

Progress so far

  • We have completed a three-year study of scoter lake selection and foraging behaviour. This study contrasted the habitat features of preferred scoter lakes with those of other lakes which have been abandoned by scoters.
  • Results have been used to develop potential conservation solutions, based on management of water levels and fish populations. These are being progressed at present.

Work planned or underway

Fieldwork took place over three seasons, April-August 2009-11.  Two comparable sets of 13 lochs, one regularly used by scoters, and one now rarely used, were compared in two study areas: the Flow Country and the West Highlands.  At each loch, we measured the abundance of aquatic invertebrates, predators, fish, and physical factors like substrates and depths.  Scoter foraging behaviour was quantified during standard watches of adults and broods. 

This work is now in the writing up phase, and is informing our conservation action for this species.


Preferred scoter lakes are characterised by a greater abundance of large-bodied aquatic invertebrates - typical prey items of breeding scoters - and by larger areas of shallow water, which may make foraging easier for scoters.

Invertebrate abundance was higher where brown trout - which also feed on aquatic invertebrates - were rarer.

There were few strong links between scoter lake use and predator occurrence - but this could partly reflect poor detection of some predators by scoters.  Introduced American mink were recorded at one important scoter breeding lake.


Who to contact

Mark Hancock
Senior Conservation Scientist


Wildfowl and Wetlands Trust (

The Conservation Volunteers (

Scottish Natural Heritage (

Environmental Research Institute (


This project is 50% funded by Scottish Natural Heritage. Other partners have also provided important in-kind assistance and funding.