Individual variability in the migratory path and stopovers of a long-distance pelagic migrant

Abstract

The analysis of repeated journeys of the same individuals is becoming an important tool in the study of animal migration. This approach has been used to analyse the migratory consistency (in schedules, routes and stopovers) of various species, with implications for the understanding of navigation mechanisms, travel strategies and conservation. However, few studies have addressed the individual consistency in pelagic long-distance migrations, in particular in the routes followed in different years. By analysing 100 journeys from 35 individual Cory's shearwaters, Calonectris diomedea, that repeatedly migrated to the South African region we examined the fidelity to migratory paths and stopovers of a transequatorial seabird migrant. Cory's shearwaters showed an overall trend to be faithful to their routes in different years, which was particularly obvious in the first (southbound) part of the outward migration. Nevertheless, we did not detect any individual consistency in the final part of the outward migration, in the return migration or in the location of the stopovers. The fact that Cory's shearwaters can be either consistent or inconsistent in different parts of their routes is possibly related to the variability of the external factors (such as wind conditions and location of good foraging areas) found along the way. Ó

Wanderer of the deepest seas: migratory behaviour and distribution of the highly pelagic Bulwer’s petrel

“…This resulted in a considerably long period away from the waters surrounding the breeding colony (216 days, on average), especially when compared to other Procellariiform species from this and adjacent colonies, such as the Cory's Shearwater Calonectris diomedea, the Zino's petrel Pterodroma madeira and the Desertas petrel Pterodroma deserta (Dias et al 2011;Zino and Biscoito 2011;Ramírez et al 2013). Failed breeders left the colony (and arrived at the wintering areas) significantly earlier than successful birds, again in contrast with the pattern revealed for Cory's Shearwater, in which breeding success do not influence the time of arrival at the wintering areas (Catry et al 2013). The migratory timings of this latter species are believed to be strongly influenced by the wind conditions in the Intertropical Convergence Zone, where the calms, near surface westerlies (10°-20°N) during the summer months (June-October), delay the southbound migration to late October and early November (Felicísimo et al 2008;Dias et al 2011Dias et al , 2013.…”

“…Failed breeders left the colony (and arrived at the wintering areas) significantly earlier than successful birds, again in contrast with the pattern revealed for Cory's Shearwater, in which breeding success do not influence the time of arrival at the wintering areas (Catry et al 2013). The migratory timings of this latter species are believed to be strongly influenced by the wind conditions in the Intertropical Convergence Zone, where the calms, near surface westerlies (10°-20°N) during the summer months (June-October), delay the southbound migration to late October and early November (Felicísimo et al 2008;Dias et al 2011Dias et al , 2013. In contrast, Bulwer's petrels crossed the area as soon as their breeding season ceased, suggesting that the seasonal variation in westerlies may not have a strong influence on smaller species.…”

Methods for detecting and quantifying individual specialisation in movement and foraging strategies of marine predators

“…Therefore, in order to apply the methods listed above (correlations and repeatability analysis), spatial data are typically reduced via summary statistics to a single dimension, or are analysed separately (e.g. Phillips et al 2005, Dias et al 2013, Ceia et al 2014, Yamamoto et al 2014, Potier et al 2015. The most common summary data derived from each trip that have been used in this way include the total duration, total distance travelled (summed great circle distances between fixes), maximum range (great circle distance to the furthest location), and bearing at departure or to the furthest point (Hamer et al 2001, 2007, Soanes et al 2013, Ceia et al 2014, Patrick et al 2014, Baylis et al 2015b, Oppel et al 2015, Potier et al 2015.…”

“…Distances can also be calculated between pairs of migratory routes (e.g. for the same individual during consecutive years), either between positions at certain landmarks (Yamamoto et al 2014), or as the mean distance between each position on one route and the nearest position on the other (Guilford et al 2011, Dias et al 2013). The smaller that distance, the more consistent the individual.…”

“…To compare the within-and between-individual distances (i.e. evaluate the statistical significance of individual consistency), one approach is to use distances calculated for pairs of centroids or routes as the response variable in a (G)LMM with individual (same vs. different) as a random effect, and check for the significance of the random effect (Dias et al 2013). The second, and more widely used approach, is to compare the calculated within-individual distances with a null distribution of distances generated by reshuffling either locations or migratory tracks between individuals (Navarro & González-Solís 2009, Dias et al 2011, McFarlane Tranquilla et al 2014).…”