Estimating dispersal distributions at multiple scales: within-colony and among-colony dispersal rates, distances and directions in European Shags Phalacrocorax aristotelis

Emily J. Barlow, Francis Daunt, Sarah Wanless, Jane M. Reid*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

24 Citations (Scopus)


Knowledge of the rate, distance and direction of dispersal within and among breeding areas is required to understand and predict demographic and genetic connectivity and resulting population and evolutionary dynamics. However dispersal rates, and the full distributions of dispersal distances and directions, are rarely comprehensively estimated across all spatial scales relevant to wild populations. We used re-sightings of European Shags Phalacrocorax aristotelis colour-ringed as chicks on the Isle of May (IoM), UK, to quantify rates, distances and directions of dispersal from natal to subsequent breeding sites both within IoM (within-colony dispersal) and across 27 other breeding colonies covering 1045km of coastline (among-colony dispersal). Additionally, we used non-breeding season surveys covering 895km of coastline to estimate breeding season detection probability and hence potential bias in estimated dispersal parameters. Within IoM, 99.6% of individuals dispersed between their natal and observed breeding nest-site. The distribution of within-colony dispersal distances was right-skewed; mean distance was shorter than expected given random settlement within IoM, yet some individuals dispersed long distances within the colony. The distribution of within-colony dispersal directions was non-uniform but did not differ from expectation given the spatial arrangement of nest-sites. However, 10% of all 460 colour-ringed adults that were located breeding had dispersed to a different colony. The maximum observed dispersal distance (170km) was much smaller than the maximum distance surveyed (690km). The distribution of among-colony dispersal distances was again right-skewed. Among-colony dispersal was directional, and differed from random expectation and from the distribution of within-colony dispersal directions. Non-breeding season surveys suggested that the probability of detecting a colour-ringed adult at its breeding location was high in the northeastern UK (98%). Estimated dispersal rates and distributions were therefore robust to incomplete detection. Overall, these data demonstrate skewed and directionally divergent dispersal distributions across small (within-colony) and large (among-colony) scales, indicating that dispersal could create genetic and demographic connectivity within the study area.

Original languageEnglish
Pages (from-to)762-778
Number of pages17
Issue number4
Early online date2 Aug 2013
Publication statusPublished - Oct 2013

Bibliographical note

We thank the National Trust (Farne Islands), Forth Seabird Group (Forth Islands), Scottish Seabird Centre (Craigleith and Fidra), Fair Isle Bird Observatory (Fair Isle), Royal Society for the Protection of Birds (Inchmickery), J. Bull (IoM), M. Frederiksen (IoM), M. Hall (IoM), M. Harris (IoM), M. Heubeck (Sumburgh Head), G. Leaper (Fowlsheugh), M. Newell (IoM), T. Reed (IoM), R. Sellers (Badbea), R.L. Swann (North Sutor), R. Duncan (Bullers of Buchan) and L. Wilson (IoM) for help with data collection and colour-ringing; Scottish Natural Heritage for access to the Isle of May National Nature Reserve; Isle of May Bird Observatory for providing BTO rings; D. Ferguson, B. Simpson, I. Watson and North 58º Sea Adventure Ltd for boat services; the numerous observers who provided winter observations, particularly R. Duncan; S. Cavers, R. Nager, M. Frederiksen and anonymous referees for thoughtful comments; and NERC (E.J.B.) and the Royal Society (J.M.R.) for funding.


  • connectivity
  • demography
  • fat-tailed distribution
  • long-distance dispersal
  • movement
  • philopatry
  • natal dispersal
  • population-dynamics
  • wandering albatross
  • survival
  • consequences
  • bird
  • size
  • recruitment
  • ecology


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