Identifying targets for conservation: the arrival and loss of Common Eider Somateria mollissima ducklings in an estuarine nursery

ABSTRACT

Capsule:

The arrival of Common Eider Somateria mollissima ducklings into a reception and nursery area is a measure of breeding success and phenology but reveals gaps in knowledge for effective conservation.

Aims:

Estuarine habitats are important wildlife areas but are continually under threat from human activities. Common Eiders may be an indicator species for monitoring the impacts of development in estuaries used by them as nursery areas. The aim of this study was to understand the arrival and distribution of ducklings in a commercial and recreational estuarine environment.

Methods:

Coquet Island, Northumberland, is a breeding site for Common Eiders at the southern limit of their range on the east coast of the UK. Numbers of ducklings arriving in the adjacent Coquet Estuary nursery area were monitored daily during the breeding season over a 27-year period from 1995 to 2021 inclusive.

Results:

Counts of ducklings were higher overall in less disturbed parts of the estuary, but there were no consistent patterns of habitat use. First-arrival dates varied annually by up to 23 days. Daily arrival counts were affected by tide and, to a lesser extent, rain and wind direction. Observed arrivals each season correlated with counts of breeding females on Coquet Island. There was evidence for links between broader-scale weather conditions (North Atlantic Oscillation indices) and yearly variation in rates of duckling arrival. Arrivals were more synchronous in years when ducklings were late in arriving and supported theoretical predictions from modelling studies. There were high daily rates of duckling loss from the estuary which may have been a consequence of brood movements out of the estuary and loss to predation. There was a positive correlation between counts of ducklings and attendant females.

Conclusions:

Annual duckling counts show the value of estuaries for monitoring phenological variation in the breeding of Common Eiders. A better understanding of environmental factors influencing duckling retention or loss in estuaries is needed. Enabling human and wildlife activities to exist together within estuarine environments may promote effective conservation.

Acknowledgements

BirdTrack data (online Figure S4) were supplied by the British Trust for Ornithology (BTO). BirdTrack is organized by the BTO for the BTO, RSPB, BirdWatch Ireland, SOC, and WOS. We thank John Steele for his vignette of Eiders, and Anne Wilson for the Coquet Island breeding Eider counts from her archive of monitoring data for Northumberland islands.

Disclosure statement

No potential conflict of interest was reported by the authors.