Interspecific variation in hatching success among three sea duck species at one breeding site in the Baltic Sea
Main Article Content
Abstract
Understanding variation in survival and reproduction is key for conservation and management of bird populations. By compiling and analysing data on hatching success (i.e. proportion of nests with at least one hatched egg) from Common Eider Somateria m. mollissima, Velvet Scoter Melanitta fusca and Red-breasted Merganser Mergus serrator, all breeding on a single island in the Baltic Sea, we demonstrate that species-specific variation can be distinct even when nests are found in the same habitat on a relatively small study site. A total of 3,316 nests was found, and hatching success was determined for 2,890 nests during a four-year study period (2021–2024). Both Common Eider and Velvet Scoter exhibited considerable interannual variation in hatching success. Hatching success for Common Eider was highest in the two last years, but in the first two years for Velvet Scoter. Red-breasted Merganser showed more stable and generally higher hatching success than the other two species. Lack of covariation between species over the years indicates that species-specific traits such as phenology and behaviour (e.g. defence-mechanisms to avoid nest predation) may override other local factors influencing breeding success. Our results suggest that knowledge of annual variation in hatching success cannot be applied to other closely related species, even when those species are found breeding in the same area and habitat and may even share nesting sites.
Article Details

This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
Articles in Wildfowl volumes 1-74 and in Wildfowl Special Issues 1-7 are not licensed under Creative Commons. In these volumes, all rights are reserved to the authors of the articles respectively.
The Wildfowl & Wetlands Trust (which published the journal from 1948–2020 inclusive) retains a royalty-free license in perpetuity to access and use pre-2021 issues for the purposes of research, which may involve sharing with research partners from time to time.
The copyright for this paper belongs to the Author(s). Papers published in Wildfowl 75 (in 2025) and subsequent issues are licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
In the articles published in these volumes, all rights are reserved to the authors of the articles respectively. This implies that readers can download, read, and link to the articles, but they cannot republish the articles. Authors can upload their articles into an institutional repository.
References
Åhlund, M. & Götmark, F. 1989. Gull predation on eider ducklings Somateria mollissima: effects of human disturbance. Biological Conservation, 48: 115–127.
Anker-Nilssen, T., Fayet, A.L. & Aarvak, T. 2023. Top-down control of a marine mesopredator: Increase in native White-tailed Eagles accelerates the extinction of an endangered seabird population. Journal of Applied Ecology 60: 445–452.
Bolduc, F. & Guillemette, M. 2003. Human disturbance and nesting success of Common Eiders: interaction between visitors and gulls. Biological Conservation 110: 77–83.
Brown, P.W. & Brown, M.A. 1981. Nesting biology of the white-winged scoter. Journal of Wildlife Management 45: 38–45.
Bustnes, J.O., Erikstad, K.E. & Bjorn, T.H. 2002. Body condition and brood abandonment in common eiders breeding in the high Arctic. Waterbirds 25: 63–66.
Christensen, T.K. & Hounisen, J.P. 2014. Managing hunted populations through sex-specific season lengths: a case of the Common Eider in the Baltic-Wadden Sea flyway population. European Journal of Wildlife Research 60: 717–726.
Craik, S.R. & Titman, R.D. 2009. Nesting ecology of Red-breasted Mergansers in a Common Tern colony in eastern New Brunswick. Waterbirds 32: 282–292.
Craik, S.R., Titman, R.D., Savard, J.P.L., Kaouass, M., Thimot, N., Elliott, K.H. & Tremblay, É. 2018. Costs and response to conspecific brood parasitism by colonial Red-breasted Mergansers. Journal of Ethology 36: 251– 258.
Dagys M. & Hearn R. 2018. International Single Species Action Plan for the Conservation of the Velvet Scoter (Melanitta fusca) W Siberia & N Europe/NW Europe Population. AEWA Technical Series No. 67. African-Eurasian Migratory Waterbird Agreement, Bonn, Germany.
Desholm, M., Christensen, T.K., Scheiffarth, G., Hario, M., Andersson, Å., Ens, B.J., Camphuysen, C.J., Nilsson, L., Waltho, C.M., Lorentsen, S.-H., Kuresoo, A., Kats, R.K.H., Fleet, D.M. & Fox, A. 2002. Status of the Baltic/Wadden Sea population of the Common Eider Somateria m. mollissima. Wildfowl 53: 167–203.
Dey, C.J., Semeniuk, C.A.D., Iverson, S.A., Richardson, E., McGeachy, D. & Gilchrist, H.G. 2018. Forecasting the outcome of multiple effects of climate change on northern common eiders. Biological Conservation 220: 94–103.
Ekblad, C.M., Sulkava, S., Stjernberg, T.G. & Laaksonen, T.K. 2016. Landscape-scale gradients and temporal changes in the prey species of the white-tailed Eagle (Haliaeetus albicilla). Annales Zoologici Fennici 53: 228– 240.
Ekroos, J., Fox, A.D., Christensen, T.K., Petersen, I.K., Kilpi, M., Jónsson, J.E et al. 2012a. Declines amongst breeding Eider Somateria mollissima numbers in the Baltic/Wadden Sea flyway. Ornis Fennica 89: 81–90.
Ekroos, J., Öst, M., Karell, P., Jaatinen, K. & Kilpi, M. 2012b. Philopatric predisposition to predation-induced ecological traps: habitat-dependent mortality of breeding Eiders. Oecologia 170: 979–986.
Erikstad, K.E. & Bustnes, J.O. 1994. Clutch size determination in Common Eiders – an egg removal and egg addition experiment. Journal of Avian Biology 25: 215–218.
Erikstad, K.E., Bustnes, J.O. & Moum, T. 1993. Clutch-size determination in precocial birds – a study of the Common Eider. Auk 110: 623–628.
Fox, A.D. 2013. Diet and habitat use of Scoters Melanitta in the Western Palearctic – a brief overview. Wildfowl 54: 163–184.
Fox, A.D., Jónsson, J.E., Aarvak, T., Bregnballe, T., Christensen, T.K., Clausen, K.K. & Therkildsen, O.R. 2015. Current and potential threats to Nordic duck populations – a horizon scanning exercise. Annales Zoologici Fennici 52: 193–220.
Fransson, T., Pettersson, J. & Larsson, P. 2001. Svensk Ringmärkningsatlas [Swedish Bird Ringing Atlas], Vol. 1. Ljungföretagen Tryckeri AB, Örebro, Sweden.
Graves, S., Piepho, H. & Dorai-Raj, L. 2024. multcompView: Visualizations of Paired Comparisons. R package version 0.1-10, https://github.com/lselzer/multcompview.
Green, M., Haas, F. & Lindström, Å. 2025. Övervakning av fåglarnas populationsutveckling. Årsrapport för 2024. Biologiska Institutionen Rapport, Lund University, Lund, Sweden.
Gunnarsson, G., Elmberg, J., Pöysä, H., Nummi, P., Sjöberg, K., Dessborn, L. & Arzel, C. 2013. Density dependence in ducks: a review of the evidence. European Journal of Wildlife Research 59: 305–321.
Hanssen, S.A., Erikstad, K.E., Johnsen, V. & Bustnes, J.O. 2003. Differential investment and costs during avian incubation determined by individual quality: an experimental study of the common eider (Somateria mollissima). Proceedings of the Royal Society B – Biological Sciences 270: 531–537.
Hario, M. & Rintala, J. 2006. Fledgling production and population trends in Finnish common Eiders (Somateria mollissima mollissima) – evidence for density dependence. Canadian Journal of Zoology 84: 1038–1046.
Hario, M., Komu, R., Muuronen, P. & Selin, K. 1986. Population trends among archipelago birds in Söderskär bird sanctuary 1963–86. Suomen Riista 33: 79–90.
Hartman, G., Kölzsch, A., Larsson, K., Nordberg, M. & Höglund, J. 2013. Trends and population dynamics of a Velvet Scoter (Melanitta fusca) population: influence of density dependence and winter climate. Journal of Ornithology 154: 837–847.
HELCOM. 2023. Abundance of waterbirds in the breeding season. HELCOM Core Indicator Report, HELCOM, Helsinki, Finland. Available at https://helcom.fi/ wp-content/uploads/2023/03/Abundance- of-waterbirds-in-breeding-season_HELCOM- core-indicator-HOLAS-II-component-2017. pdf (last accessed 5 July 2025).
Hentati-Sundberg, J., Melchiori, S., Berglund, P.A. & Olsson, O. 2023. Eagle effects on seabird productivity: Effects of a natural experiment. Biological Conservation 284: 110–145.
Hermansson, I., von Numers, M., Jaatinen, K. & Öst, M. 2023. Predation risk and landscape properties shape reproductive output of an endangered sea duck from two subpopulations with contrasting predation risk. Journal of Ornithology 164: 311–326.
Jaatinen, K., Hermansson, I., Mohring, B., Steele, B.B. & Öst, M. 2022. Mitigating impacts of invasive alien predators on an endangered seaduck amidst high native predation pressure. Oecologia 198: 543–552.
Kiknavelidze, S., Kopaliani, N., Budagashvili, N., Melikishvili, N., Javakhishvili, Z., Gavashelishvili, A. & Paposhvili, N. 2024. Nesting behaviour and factors affecting reproductive success of Velvet Scoter Melanitta fusca breeding at Lake Tabatskuri Georgia. Wildfowl 74: 179–192.
Kilpi, M., Lorentsen. S.H., Petersen, I.K. & Einarsson, A. 2015. Trends and drivers of change in diving ducks. TemaNord Report No. 2015:516, Nordic Council of Ministers, Copenhagen, Denmark.
Krone, O., Nadjafzadeh, M. & Berger, A. 2013. White-tailed Sea Eagles (Haliaeetus albicilla) defend small home ranges in north-east Germany throughout the year. Journal of Ornithology 154: 827–835.
Laursen, K. & Møller, A.P. 2022. Diet of Eiders and body condition change from the late 1980s to the mid-2010s. Journal of Sea Research 187: 102244.
Lehikoinen, P., Alhainen, M., Frederiksen, M., Jaatinen, K., Juslin, R., Kilpi, M., Mikander, N. & Nagy, S. (compilers). 2022. International Single Species Action Plan for the Conservation of the Common Eider Somateria m. mollissima (Baltic, North & Celtic Seas, and Norway & Russia Populations) and S. m. borealis (Svalbard & Franz Josef Land Population). AEWA Technical Series No. 75. African-Eurasian Migratory Waterbird Agreement, Bonn, Germany.
Leighton, P.A., Horrocks, J.A. & Kramer, D.L. 2010. Conservation and the scarecrow effect: Can human activity benefit threatened species by displacing predators? Biological Conservation 143: 2156–2163.
Lötberg, U., Isaksson, N., Söderlund, L. & Åkesson, S. 2022. Conservation measures for the Caspian Tern Hydroprogne caspia at the largest colony in Sweden. Ornis Svecica 32: 26–37.
Madsen, J., Bunnefeld, N., Nagy, S., Griffin, C., Defos du Rau, P., Mondain-Monval, J.Y., Hearn, R., Czajkowski, A., Grauer, A., Merkel, F.R., Williams, J.H., Alhainen, M., Guillemain, M., Middleton, A., Christensen, T.K. & Noe, O. 2015. Guidelines on Sustainable Harvest of Migratory Waterbirds. AEWA Conservation Guidelines No. 5, AEWA Technical Series No. 62. African-Eurasian Migratory Waterbird Agreement, Bonn, Germany.
Mohring, B., Angelier, F., Jaatinen, K., Steele, B., Lönnberg, E. & Öst, M. 2022. Drivers of within- and among-individual variation in risk-taking behaviour during reproduction in a long-lived bird. Proceedings of the Royal Society 289: 1983.
Nicol-Harper, A., Wood, K.A., Diamond, A.W., Major, H.L., Petersen, A., Tertitski, G. & Hilton, G.M. 2021. Vital rate estimates for the common eider Somateria mollissima, a data-rich exemplar of the seaduck tribe. Ecological Solutions and Evidence 2: e12108.
Nordström, M., Högmander, J., Nummelin, J., Laine, J., Laanetu, N. & Korpimäki, E. 2002. Variable responses of waterfowl breeding populations to long-term removal of introduced American mink. Ecography 25: 385–394.
Öst, M. & Steele, B.B. 2010. Age-specific nest-site preference and success in Eiders. Oecologia 162: 59–69.
Öst, M., Ramula, S., Lindén, A., Karell, P. & Kilpi, M. 2016. Small-scale spatial and temporal variation in the demographic processes underlying the large-scale decline of Eiders in the Baltic Sea. Population Ecology 58: 121–133.
Öst, M., Lindén, A., Karell, P., Ramula, S. & Kilpi, M. 2018. To breed or not to breed: drivers of intermittent breeding in a seabird under increasing predation risk and male bias. Oecologia 188: 129–138.
Özkoç, Ö.Ü., Paposhvili, N., Aghababyan, K., Petersen, I.K. & Fox, A.D. 2025. Contraction of range, declines in abundance and site-based threats to Velvet Scoter Melanitta fusca breeding in the Caucasus. Wildfowl 75: 159–184.
R Core Team. 2024. R: A Language and Environment for Statistical Computing. R Foundation for Statistical Computing, Vienna, Austria.
Rintala, J., Hario, M., Laursen, K. & Møller, A.P. 2022. Large-scale changes in marine and terrestrial environments drive the population dynamics of long-tailed ducks breeding in Siberia. Scientific Reports 12(1): 12355.
Sénéchal, É., Bêty, J., Gilchrist, H.G., Hobson, K.A. & Jamieson, S.E. 2011. Do purely capital layers exist among flying birds? Evidence of exogenous contribution to arctic-nesting common eider eggs. Oecologia 165: 593–604.
Sjöberg, K. 1985. Foraging activity patterns in the goosander (Mergus merganser) and the red-breasted Merganser (M. serrator) in relation to patterns of activity in their major prey species. Oecologia 67: 35–39.
Skov, H. 2011. Waterbird Populations and Pressures in the Baltic Sea. TemaNord Report No. 2011:550. Nordic Council of Ministers, Copenhagen, Denmark.
Stien, J. & Ims, R.A. 2016. Absence from the nest due to human disturbance induces higher nest predation risk than natural recesses in Common Eiders Somateria mollissima. Ibis 158: 249–260.
Stien, J., Yoccoz, N.G. & Ims, R.A. 2010. Nest predation in declining populations of common eiders Somateria mollissima: an experimental evaluation of the role of hooded crows Corvus cornix. Wildlife Biology 16: 123–134.
Swennen, C., Ursem, J.C.H. and Duiven, P. 1993. Determinate laying and egg attendance in Common Eiders. Ornis Scandinavica 24: 48–52.
Thimot, N.J., Titman, R.D., Elliott, K.H. & Craik, S.R. 2020. Conspecific brood parasitism in an upland-nesting bird: cues parasites use to select a nest. Behavioral Ecology and Sociobiology 74: 1–11.
Tjørnløv, R.S. 2019. Population dynamics of a declining flyway population of Common Eiders Somateria mollissima. Ph.D. thesis, Aarhus University, Aarhus, Denmark.
Traylor, J.J., Alisauskas, R.T. & Kehoe, F.P. 2004. Nesting ecology of white-winged scoters (Melanitta fusca deglandi) at Redberry Lake, Saskatchewan. Auk 121: 950–962.