Insights on dispersal and recruitment paradigms: sex- and age-dependent variations in a nomadic breeder

Abstract

Sex- and age-dependence in recruitment and dispersal are often explained by costs arising from competition for holding a breeding territory over the years-a typical feature of species living in stable habitats. For instance, long-lived birds with male territoriality often exhibit large variation in recruitment age and higher dispersal in females and young individuals. As a corollary, we expected that species with ephemeral habitat suitability, and hence nomadic breeding, would show weak age- and sex-dependence in dispersal and low variation in recruitment age, because territory ownership is not maintained over the years. In addition, the higher cost of reproduction in females might not be (over)compensated for by costs of territoriality in males. Accordingly, females would recruit later than males. We explored these variations using multievent capture-recapture models over 13 years, 3479 (2392 sexed) slender-billed gulls (Chroicocephalus genei) and 45 colony sites along the French Mediterranean coast. As expected, variability in recruitment age was low with males recruiting earlier than females. Nonetheless, dispersal in and out of the study area decreased with age and was slightly higher in males than in females. Decreased dispersal with age might result from foraging benefits associated with increased spatial familiarity. Higher dispersal in males might be explained by a male-biased sex ratio or higher philopatry benefits in females (arising from their higher cost of reproduction). Sex- and age-dependent dispersal and recruitment may thus occur in the absence of year-to-year breeding territory ownership, which stresses the importance of considering other processes in shaping recruitment and dispersal patterns.

Breeding transients in capture–recapture modeling and their consequences for local population dynamics

“…Despite the high occurrence of transients, results of these analyses are rarely considered as a way to explore or quantify the ecological processes behind the occurrence of transients. This is so even in studies finding transients considering a two-ages classes in the starting model, when newborns were included in the analysis 14,37 , or in studies working only with breeding adults 19,38 . While mortality after first reproduction is a direct fitness cost, permanent dispersal is not necessarily a cost to an individual, but may still have consequences to the local population growth rate.…”

Foraging niche shift maintains breeding parameters of a colonial waterbird during range expansion

“…Interestingly, a lower breeding success was found during the second period of the study marked with high emigration rate outside the south of France and first colony settlements outside saltpans (Acker et al, ). However, Slender‐billed gulls were able to maintain their breeding parameters during the consecutive periods of range expansion despite a noticeable change in diet.…”

“…We distinguished four periods based on the spatial dynamics of the species: (a) 1998–2000 corresponding to a period when all colonies were located in the saltpans of the Camargue, either at Salin‐de‐Giraud or at Aigues‐Mortes; (b) 2001–2005 marked by first colony settlements outside saltpans and high emigration rates outside France (Acker et al, ); (c) 2006–2010 corresponding to the return of many individuals back from outside the study area and the subsequent colonization of Grand Bastit and Hyères; (d) 2011–2013 corresponding to the stabilization of a set of colonies outside the Camargue.…”

“…Range expansion may then have resulted from other processes such as a behavioral adaptation to habitat unpredictability. Indeed, the Slender-billed gull present low site tenacity as shown for the population breeding in southern France (Acker et al, 2017). Its ability to change colony site from one year to another is likely an adaptation to environmental stochasticity (Sanz-Aguilar et al, 2014).…”

Contrasting patterns of population structure at large and fine geographical scales in a migratory avian disturbance specialist of braided river ecosystems

“…changing sites from one breeding season to the next; Cabot & Nisbet, ; Møller, Flensted‐Jensen, & Mardal, ). Sex‐biased dispersal has been documented for other tern species (Becker, Ezard, Ludwigs, Sauer‐Gürth, & Wink, ), but it is not very well understood for species that nest in ephemeral habitat (Acker et al, ). Black‐fronted tern breeding colonies often form in the same general vicinity, but locations also vary between years (Bell, ; Hamblin, ; Keedwell, ).…”