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Vital rate estimates for the common eider Somateria mollissima, a data-rich exemplar of the seaduck tribe


Nicol-Harper, Alex et al. (2021), Vital rate estimates for the common eider Somateria mollissima, a data-rich exemplar of the seaduck tribe, Dryad, Dataset,


This database contains estimates of the following vital rates (as required to parameterise matrix population models), for the common eider (Somateria mollissima): 1st year survival (measured either from hatching, or from fledging, to 1 year old); 2nd year survival; adult annual survival; first breeding (both age-specific recruitment probability, and breeding propensity across potential recruitment ages); breeding propensity of established female breeders; clutch size; hatching success; and fledging success. These estimates are drawn from 134 studies, across the scientific and grey literature – including three previously inaccessible datasets on clutch size that were contributed in response to a call for data through the IUCN Species Survival Commission’s Duck Specialist Group (IDs 127, A and B). This is a relational database, linking estimates and associated metadata to the relevant study (or unique unpublished combination thereof) by a unique ID number in the 'MASTER' sheet. For further information, refer to the associated publication, and/or explanatory notes on the column headings of each sheet (.xlsx version only, but provided in the dataset README .txt file).


We surveyed published academic and grey literature via keyword searches (e.g. “Somateria mollissima” “clutch size”) through Google Scholar, ‘citation snowballing’ (pursuing reference trails; see e.g. Greenhalgh & Peacock, 2005), and cross-referencing authors’ personal databases. Additionally, a call for data was posted on the IUCN Species Survival Commission’s Duck Specialist Group website (, circulated through the corresponding mailing list, and advertised by ANH on Twitter in January 2019 and at conferences (the British Ecological Society’s ‘Quantitative Ecology’ meeting in July 2019; the European Ornithologists’ Union Conference in August 2019; and the Ecological Society of America’s annual meeting in August 2020) thereafter. The call for data elicited three previously inaccessible datasets, of which one was recorded in Icelandic and another in Russian, broadening language coverage since non-English language reports were otherwise only covered by citations in English-language publications. 

Accessible vital rate estimates, and associated metadata, were collated in a relational database in Microsoft Excel, linked by a unique ID number associated with each study (or unique unpublished combinations thereof). A list of data sources used in the study are provided in the Data sources section of the associated publication. We focussed on the vital rates required to parameterise matrix population models (MPMs), which are used widely by population ecologists and conservation biologists to project population dynamics over time. We therefore included the following vital rates: 1st year survival (measured either from hatching, or from fledging, to 1 year old), 2nd year survival, adult survival, breeding propensities for 2- to 5-year-olds (both probability of having recruited at a given age, and breeding propensity at a given age), adult female breeding propensity, clutch size, hatching success and fledging success (alternatively included in 1st year survival where measured from hatching). We define: (i) hatching success as the proportion of all laid eggs that hatch (if probability of successful nesting – i.e. of at least one egg hatching – was provided, we used it to calculate hatching success where feasible), and (ii) fledging success as the proportion of hatchlings that fledge.

Where provided by the authors, we recorded the following metadata at the study level: location (country and geographic coordinates); subspecies; and population trend (classified as increasing, decreasing, stable, or variable). Further, for each estimate we recorded: sample size; variance measures (as provided and/or calculable from reported information); start and end years; and any covariates (freeform).

We did not formally screen studies, preferring instead to provide as complete a reference database as possible. We facilitate filtering with the following assignations: verification status (whether the source was seen in the original or cited by another verified source); precision (some estimates were simply the midpoints of observed ranges); and independence (which is not met when multiple estimates are provided by the same study, or when separate studies are based on the same datasets).


Greenhalgh, T., & Peacock, R. (2005). Effectiveness and efficiency of search methods in systematic reviews of complex evidence: Audit of primary sources. British Medical Journal, 331(7524), 1064–1065.

Usage Notes

The database is available in full as an xlsx spreadsheet (including header comments providing further information), or as a series of csv files for each sheet (comments not included, although they are provided in the dataset README .txt file). 

The ‘master’ sheet provides study-level information, with each study being assigned a unique identifier: numeric 1-127 for published studies, upper case A-B for unpublished contributed datasets (ID 127/Ragnarsdóttir et al., 2021 was contributed through the call for data but is published online, as an Icelandic-language publication not accessible through English-language searches), and lower case aa-ee for combinations of datasets reported in published studies (such as the combination: “Nyegaard, 2004 [thesis]; H.G. Gilchrist unpubl. data” reported in Gilliland et al., 2009, Table 1). Estimates and associated metadata for each vital rate are then recorded in separate sheets, with the ID column relating back to the studies in the ‘master’ sheet. Vital rate sheets include columns to replace imprecise overall study-level population growth rate, geographical coordinates, and subspecies entries where appropriate; for example, if the study provided vital rate data for each of several locations. Further information specific to each column can be found in comment boxes associated with the headers (.xlsx file only), and both studies and estimates are further annotated in ‘Comments’ columns where relevant. A text file with an English translation by AP of the summary from ID 127/Ragnarsdóttir et al., 2021 is also provided (see Nicol-Harper_202110_VitalRates_RagnarsdottirTranslation.txt).

The two forms of breeding propensities for 2- to 5-year-olds correspond to two of the recruitment quantities discussed in Pradel & Lebreton (1999): the probability of having recruited at a given age, which sums to 1 across all possible ages of recruitment, is equivalent to their αi (specifically, the second version described on p. S80); breeding propensities at age i (2 ≤ i ≤ 5) correspond to their ai. Vital rates referring to subadults are assumed to refer to both sexes, whereas adult survival may refer to either sex or both (specified in the database), while adult breeding propensity has thus far only been estimated for females.


Pradel, R., & Lebreton, J.-D. (1999). Comparison of different approaches to the study of local recruitment of breeders. Bird Study, 46(sup1), S74–S81.

Ragnarsdóttir, S. B., Thorstensen, S., & Metúsalemsson, S. (2021). Fuglalíf í óshólmum Eyjafjarðarár: könnun 2020 með samanburði við fyrri ár. [The birdlife of the delta area of river Eyjafjaðará, N-Iceland: The results of a survey in year 2020 in comparison to former years.] Náttúrufræðistofnun Íslands NÍ21001. 62 pp. (In Icelandic). Available at: accessed 5th October 2021.

Gilliland, S. G., Grant Gilchrist, H., Rockwell, R. F., Robertson, G. J., Savard, J.-P. L., Merkel, F., & Mosbech, A. (2009). Evaluating the Sustainability of Harvest Among Northern Common Eiders Somateria mollissima borealis in Greenland and Canada. Wildlife Biology, 15(1), 24–36.


Natural Environment Research Council, Award: NE/L002531/1

Environment and Climate Change Canada

Natural Sciences and Engineering Research Council of Canada

New Brunswick Wildlife Trust Fund

Sir James Dunn Wildlife Research Fund