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Site fidelity and individual variation in winter location in partially migratory European shags.

Grist H, Daunt F, Wanless S, Nelson EJ, Harris MP, Newell M, Burthe S, Reid JM - PLoS ONE (2014)

Bottom Line: If individuals show high within- and among- year fidelity to specific locations, any annual environmental effect on individual life histories could be reinforced, causing substantial demographic heterogeneity.Repeatability did not differ significantly between males and females or among different age classes, either within or among winters.Such high among-individual variation and within-individual repeatability, both within and among winters, could lead to substantial life history variation, and therefore influence population dynamics and future conservation management strategies.

View Article: PubMed Central - PubMed

Affiliation: Institute of Biological and Environmental Sciences, University of Aberdeen, Aberdeen, Aberdeenshire, United Kingdom; Centre for Ecology and Hydrology, Penicuik, Midlothian, United Kingdom; Scottish Ornithologists' Club, Aberlady, East Lothian, United Kingdom.

ABSTRACT
In partially migratory populations, individuals from a single breeding area experience a range of environments during the non-breeding season. If individuals show high within- and among- year fidelity to specific locations, any annual environmental effect on individual life histories could be reinforced, causing substantial demographic heterogeneity. Quantifying within- and among- individual variation and repeatability in non-breeding season location is therefore key to predicting broad-scale environmental impacts on the dynamics of partially migratory populations. We used field resightings of colour-ringed adult European shags known to have bred on the Isle of May, Scotland, to quantify individual variation and repeatability in winter location within and among three consecutive winters. In total, 3797 resightings of 882 individuals were recorded over 622 km of coastline, including the Isle of May. These individuals comprised over 50% of the known breeding population, and encompassed representative distributions of ages and sexes. The distances from the Isle of May at which individuals were resighted during winter varied substantially, up to 486 km and 136 km north and south respectively and including the breeding colony on the Isle of May. However, resighting distances were highly repeatable within individuals; within- and among-winter repeatabilities were >0.72 and >0.59 respectively across the full September-March observation period, and >0.95 and >0.79 respectively across more restricted mid-winter periods. Repeatability did not differ significantly between males and females or among different age classes, either within or among winters. These data demonstrate that the focal shag population is partially migratory, and moreover that individuals show highly repeatable variation in winter location and hence migration strategy across consecutive winters. Such high among-individual variation and within-individual repeatability, both within and among winters, could lead to substantial life history variation, and therefore influence population dynamics and future conservation management strategies.

Show MeSH
Movement boundaries.The percentages of colour-ringed adult shags known to have bred on the Isle of May that were resighted on or near the Isle of May and at an alternative winter site during winters A. 2009–2010, B. 2010–2011, and C. 2011–2012 that were away from the Isle of May on progressive dates. Dotted lines indicate 10% intervals, dashed lines denote the movement boundaries used to subset the data for repeatability analyses (0%, 30%, 60%, 90%).
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pone-0098562-g002: Movement boundaries.The percentages of colour-ringed adult shags known to have bred on the Isle of May that were resighted on or near the Isle of May and at an alternative winter site during winters A. 2009–2010, B. 2010–2011, and C. 2011–2012 that were away from the Isle of May on progressive dates. Dotted lines indicate 10% intervals, dashed lines denote the movement boundaries used to subset the data for repeatability analyses (0%, 30%, 60%, 90%).

Mentions: Individual shags were considered to still be at or have returned to the breeding colony if they were resighted on the Isle of May or at an associated day roost in the Firth of Forth (Figure 1). Across all three full winter field seasons, 237 individuals were initially resighted on or near the Isle of May and subsequently resighted at a different site, and 89 individuals were resighted at a different winter site and then back on or near the Isle of May towards the end of the same winter. These individual movements were used to estimate time intervals (hereafter “movement boundaries”) when specific percentages (from 0% to 90% in 10% increments) of individuals had departed from or returned to the Isle of May, taking the last autumn and first spring dates on which an individual was observed on or near the Isle of May as the departure and return dates respectively (Figure 2). The resulting movement boundaries are properties of the current datasets, given patchy observation dates at current survey sites, and may not reflect the migration dates of the entire population.


Site fidelity and individual variation in winter location in partially migratory European shags.

Grist H, Daunt F, Wanless S, Nelson EJ, Harris MP, Newell M, Burthe S, Reid JM - PLoS ONE (2014)

Movement boundaries.The percentages of colour-ringed adult shags known to have bred on the Isle of May that were resighted on or near the Isle of May and at an alternative winter site during winters A. 2009–2010, B. 2010–2011, and C. 2011–2012 that were away from the Isle of May on progressive dates. Dotted lines indicate 10% intervals, dashed lines denote the movement boundaries used to subset the data for repeatability analyses (0%, 30%, 60%, 90%).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4043777&req=5

pone-0098562-g002: Movement boundaries.The percentages of colour-ringed adult shags known to have bred on the Isle of May that were resighted on or near the Isle of May and at an alternative winter site during winters A. 2009–2010, B. 2010–2011, and C. 2011–2012 that were away from the Isle of May on progressive dates. Dotted lines indicate 10% intervals, dashed lines denote the movement boundaries used to subset the data for repeatability analyses (0%, 30%, 60%, 90%).
Mentions: Individual shags were considered to still be at or have returned to the breeding colony if they were resighted on the Isle of May or at an associated day roost in the Firth of Forth (Figure 1). Across all three full winter field seasons, 237 individuals were initially resighted on or near the Isle of May and subsequently resighted at a different site, and 89 individuals were resighted at a different winter site and then back on or near the Isle of May towards the end of the same winter. These individual movements were used to estimate time intervals (hereafter “movement boundaries”) when specific percentages (from 0% to 90% in 10% increments) of individuals had departed from or returned to the Isle of May, taking the last autumn and first spring dates on which an individual was observed on or near the Isle of May as the departure and return dates respectively (Figure 2). The resulting movement boundaries are properties of the current datasets, given patchy observation dates at current survey sites, and may not reflect the migration dates of the entire population.

Bottom Line: If individuals show high within- and among- year fidelity to specific locations, any annual environmental effect on individual life histories could be reinforced, causing substantial demographic heterogeneity.Repeatability did not differ significantly between males and females or among different age classes, either within or among winters.Such high among-individual variation and within-individual repeatability, both within and among winters, could lead to substantial life history variation, and therefore influence population dynamics and future conservation management strategies.

View Article: PubMed Central - PubMed

Affiliation: Institute of Biological and Environmental Sciences, University of Aberdeen, Aberdeen, Aberdeenshire, United Kingdom; Centre for Ecology and Hydrology, Penicuik, Midlothian, United Kingdom; Scottish Ornithologists' Club, Aberlady, East Lothian, United Kingdom.

ABSTRACT
In partially migratory populations, individuals from a single breeding area experience a range of environments during the non-breeding season. If individuals show high within- and among- year fidelity to specific locations, any annual environmental effect on individual life histories could be reinforced, causing substantial demographic heterogeneity. Quantifying within- and among- individual variation and repeatability in non-breeding season location is therefore key to predicting broad-scale environmental impacts on the dynamics of partially migratory populations. We used field resightings of colour-ringed adult European shags known to have bred on the Isle of May, Scotland, to quantify individual variation and repeatability in winter location within and among three consecutive winters. In total, 3797 resightings of 882 individuals were recorded over 622 km of coastline, including the Isle of May. These individuals comprised over 50% of the known breeding population, and encompassed representative distributions of ages and sexes. The distances from the Isle of May at which individuals were resighted during winter varied substantially, up to 486 km and 136 km north and south respectively and including the breeding colony on the Isle of May. However, resighting distances were highly repeatable within individuals; within- and among-winter repeatabilities were >0.72 and >0.59 respectively across the full September-March observation period, and >0.95 and >0.79 respectively across more restricted mid-winter periods. Repeatability did not differ significantly between males and females or among different age classes, either within or among winters. These data demonstrate that the focal shag population is partially migratory, and moreover that individuals show highly repeatable variation in winter location and hence migration strategy across consecutive winters. Such high among-individual variation and within-individual repeatability, both within and among winters, could lead to substantial life history variation, and therefore influence population dynamics and future conservation management strategies.

Show MeSH