Mergus serrator (Linnaeus, 1758)
Family: Anseriformes > Anatidae
One of three species of ‘sawbill’ that regularly occur in the UK, the Red-breasted Merganser can be told by its punk-style ‘hairdo’, glossy green in the male and rusty orange-red in the female.
The small breeding population is found mainly on Scottish lochs but pairs also use favoured waterbodies in western Britain and in Ireland.
Like many wildfowl, numbers grow during the winter and a wintering population of over 10,000 birds is not unusual. During the winter the Red-breasted Merganser is found almost exclusively on the sea, hunting small fish close to shore; Bird Atlas 2007–11 underlines that the species can be seen almost anywhere around our coast.
Select a topic for more facts and statistics about the Red-breasted Merganser
Red-breasted Merganser identification is often straightforward. The following article may help when identifying Red-breasted Merganser.
Identifying the two large sawbills, Goosander and Red-breasted Merganser, can be pretty straight-forward when confronted with male birds. However, the females, or redheads as they are more often called, can be much more difficult. This video gives useful pointers on how to confidently tell them apart.
Listen to example recordings of the main vocalisations of Red-breasted Merganser, provided by xeno-canto contributors.
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Status and Trends
Population size and trends and patterns of distribution based on BTO surveys and atlases with data collected by BTO volunteers.
This species can be found on the following statutory and conservation listings and schedules.
Red-breasted Merganser was added to the list of species monitored by the RBBP in 2017, after the British breeding population was estimated at 1,565 (1,373–1,754) pairs (Humphreys et al. 2016). The main breeding strongholds are in Scotland (1,432 pairs), with smaller breeding concentrations also occurring in parts of northern England, north Wales and northern Ireland. Population trends are unclear but the breeding range has decreased by 28% since 1968–72 (Balmer et al. 2013).
|UK winter population||-44% decrease (1995/96 to 2020/21)|
In winter, Red-breasted Mergansers are widely distributed around the coast of Britain & Ireland, with distinct concentrations off western Scotland, the Northern Isles, northwest and southwest Ireland, north Wales and the Solent. In the breeding season they are more concentrated in the Scottish Isles, northwest Scotland, parts of north and west Ireland, northern England and northwest Wales.
Occupied 10-km squares in UK
|No. occupied in breeding season||572|
|% occupied in breeding season||19|
|No. occupied in winter||1051|
|% occupied in winter||35|
European Distribution Map
The breeding range of the Red-breasted Merganser has contracted by 28% since the 1968–72 Breeding Atlas, with losses concentrated in western Ireland, southwest Scotland and many inland parts of Scotland, particularly in the east and far north.
Change in occupied 10-km squares in the UK
|% change in range in breeding season (1968–72 to 2008–11)||-20.2%|
|% change in range in winter (1981–84 to 2007–11)||+14.4%|
Red-breasted Mergansers are present year-round, with wintering birds on many coasts and a localised breeder in the north.
Information about movement and migration based on online bird portals (e.g. BirdTrack), Ringing schemes and tracking studies.
Lifecycle and body size information about Red-breasted Merganser, including statistics on nesting, eggs and lifespan based on BTO ringing and nest recording data.
View number ringed each year in the Online Ringing Report
|Maximum Age from Ringing||12 years 0 months 15 days (set in 2001)|
|Ring size||G or F*|
|Field Codes||2-letter: RM | 5-letter code: REBME | Euring: 2210|
For information in another language (where available) click on a linked name
Interpretation and scientific publications about Red-breasted Merganser from BTO scientists.
Causes of change
The breeding population trend is unclear: range declines suggest that a population decline may have occurred but there are insufficient data to confirm this. Causes of the possible decline are also unknown, although there are concerns about the potential impact of piscivorous birds, including Red-breasted Merganser, on fisheries and licensed control of fish-eating birds is available to reduce potential economic losses (Humphreys et al. 2016).
Abundance, distribution and habitat use of Goosanders Mergus merganser and Red-breasted Mergansers Mergus serrator on British rivers
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