Sex Promotes Spatial and Dietary Segregation in a Migratory Shorebird during the Non-Breeding Season

Abstract

Several expressions of sexual segregation have been described in animals, especially in those exhibiting conspicuous dimorphism. Outside the breeding season, segregation has been mostly attributed to size or age-mediated dominance or to trophic niche divergence. Regardless of the recognized implications for population dynamics, the ecological causes and consequences of sexual segregation are still poorly understood. We investigate the foraging habits of a shorebird showing reversed sexual dimorphism, the black-tailed godwit Limosa limosa, during the winter season, and found extensive segregation between sexes in spatial distribution, microhabitat use and dietary composition. Males and females exhibited high site-fidelity but differed in their distributions at estuary-scale. Male godwits (shorter-billed) foraged more frequently in exposed mudflats than in patches with higher water levels, and consumed more bivalves and gastropods and fewer polychaetes than females. Females tended to be more frequently involved and to win more aggressive interactions than males. However, the number of aggressions recorded was low, suggesting that sexual dominance plays a lesser role in segregation, although its importance cannot be ruled out. Dimorphism in the feeding apparatus has been used to explain sex differences in foraging ecology and behaviour of many avian species, but few studies confirmed that morphologic characteristics drive individual differences within each sex. We found a relationship between resource use and bill size when pooling data from males and females. However, this relationship did not hold for either sex separately, suggesting that differences in foraging habits of godwits are primarily a function of sex, rather than bill size. Hence, the exact mechanisms through which this segregation operates are still unknown. The recorded differences in spatial distribution and resource use might expose male and female to distinct threats, thus affecting population dynamics through differential mortality. Therefore, population models and effective conservation strategies should increasingly take sex-specific requirements into consideration.

Patterns and processes in shorebird survival rates: a global review

“…The degree to which models that generate estimates of true survival differ from estimates on the apparent survival depends on the proportion of individuals that emigrate (Sandercock 2003(Sandercock , 2006. However, we found no systematic differences between estimates generated through recovery or more complex models and those generated via mark-recapture models, which is likely to reflect the fact that most shorebirds are highly site-faithful, returning to the same breeding and non-breeding sites throughout their life (Burton & Evans 1997, Leyrer et al 2006, Catry et al 2012. Recovery and more complex models could fail to account for permanent emigration out of study areas if data collection were restricted to specific sites, resulting in estimates of apparent rather than true annual survival (Cohen et al 2006, Roodbergen et al 2008.…”

“…, Catry et al . ). Recovery and more complex models could fail to account for permanent emigration out of study areas if data collection were restricted to specific sites, resulting in estimates of apparent rather than true annual survival (Cohen et al .…”

Structure and functioning of intertidal food webs along an avian flyway: a comparative approach using stable isotopes

“…At Tejo estuary and Sidi Moussa, where more information on shorebird diet was already available (e.g. Kersten et al 1981;Moreira 1994;Lourenc ßo et al 2008;Catry et al 2012a), sampling of macroinvertebrates was less extensive than at the remaining areas.…”

Habitat suitability modeling in different sperm whale social groups

“…On a global scale, this leads to different dispersal patterns and segregation by sex, with male sperm whales feeding in high latitudes and females limited mainly to low latitudes (Lyrholm et al ); on a local (Mediterranean Sea) scale, sperm whale groups by sex class may be found in sympatry (Pirotta et al , Frantzis et al , Pace et al , Rendell and Frantzis ), with indications of fine‐scale partitioning and different habitat preference of singletons and groups in a given region (Pirotta et al , Jones et al ). Dissimilarities in habitat choices made by males and females in different social assemblages may have also practical implications for the effective management of a population because differences in spatial distribution and resource use might expose males and females to distinct threats, thus affecting population dynamics through differential mortality risk (Catry et al ).…”