Strong temporal consistency in the individual foraging behaviour of Imperial Shags Phalacrocorax atriceps

Abstract

Individual consistency in foraging behaviour can generate behavioural variability within populations and may, ultimately, lead to species diversification. However, individualbased long-term behavioural studies are particularly scarce in seabird species. Between 2008 and 2011, breeding Imperial Shags Phalacrocorax atriceps at the Punta Le on colony, Argentina, were tracked with GPS devices to evaluate behavioural consistency during their foraging trips. Within a breeding season, individuals were highly consistent in the maximum distances they reached from the shore and the colony, as well as in the time invested in flight and diving across consecutive days during early chick rearing. In addition, each individual had its specific foraging area distinct from the foraging area of other individuals. Comparing between early and late chick rearing in the same season, individuals were consistent, to a lesser degree, in the maximum distance they reached from the colony and the shore, increasing in consistency later on in the season. Within the season, females were more consistent than males in the maximum distance they moved from the colony and the shore, the sexes segregated in their foraging areas and individual females were segregated from one another. Twenty-eight individuals tracked in different breeding seasons were marginally consistent in their trip durations and maximum distance reached from shore across seasons. Among seasons, foraging locations differed between sexes and among individual females. Individuals from this colony exhibited consistency over time in several aspects of foraging behaviour, which may be due to a combination of individual characteristics such as learning abilities, breeding experience or health, as well as targeted prey type and stability of the environment at this location.

Combined bio-logging and stable isotopes reveal individual specialisations in a benthic coastal seabird, the Kerguelen shag

“…Other species from the blue-eyed shag complex show dietary specialisations that can be maintained over long timescales, consistent with the ability of some animals to adopt long-term behavioural strategies [3, 20, 32, 33]. …”

“…The difference in consistency in maximum depths between males and females, however, is in line with values reported in [20, 56] who proposed differential degrees of individual specialisation within sexes as a mechanism for vertical niche partitioning. Harris et al did not report differences in consistency between sexes in the depth of area-restricted search (ARS) areas but identified differences in consistency in other aspects of the foraging behaviour of the Imperial shags they instrumented; indeed females were more consistent in the maximum distances reached from the colony and the shore [33]. They suggested that these differences might be linked with sexual dimorphism, which constrains one sex more than the other and reduces their behavioural plasticity.…”

Intra- and inter-individual variation in the foraging ecology of a generalist subantarctic seabird, the gentoo penguin

“…This suggests that gentoos stay consistent in some aspects of their foraging behaviour, which may help to reduce intra-specific competition and/or may allow individuals to catch prey they can easily handle and digest (Bolnick et al 2003, Estes et al 2003. This seems particularly relevant in inshore foragers, as they are restricted in their foraging range (Cook et al 2006, Ratcliffe et al 2013, Harris et al 2014.…”

“…In order to quantify the intra-individual variation in diving behaviour and spatial use, we used the R package ape (Paradis et al 2004) to perform a variance component analysis. This method calculates the variance, standard deviation and proportion of total variance occurring at the levels of individual, and trip within individual when multiple observations per trip were obtained, as well as the residual variation (Ratcliffe et al 2013, Harris et al 2014). An estimate of individual specialisation is given by the proportion of variance explained by the individual variance component (Bolnick et al 2003, Dingemanse & Dochtermann 2013, Ratcliffe et al 2013).…”

Plasma Biochemistries and Morphometric Indices of Body Condition in Imperial Cormorant (Phalacrocorax atriceps) Chicks

“…We found marked inter-annual variation in all biochemical parameters analyzed in Imperial Cormorant chicks. Although previous studies in the same colony showed that foraging behavior and feeding locations of breeding Imperial Cormorants are highly consistent within and between breeding seasons (Quintana et al 2011;Harris et al 2014), part of the inter-annual variability in chick chemistries may be explained by differential nutrient profiles of prey consumed by parents (see also González Miri and Malacalza 1999). Also contrary to our expectations, the breeding season that showed the highest mean values for plasma biochemistries (2011) coincided with that of lower productivity of the colony in terms of number of chicks fledged (based on average estimates over a period of 9 years; W. S. Svagelj and F. Quintana, unpubl.…”