Intra-sexual female agonistic behaviour of the South American sea lion (Otaria flavescens) in two colonies with different breeding substrates

Abstract

Female agonistic behaviour during pregnancy and lactation is common in several pinnipeds and has been associated to pup or territory defence. Previous studies on female agonistic behaviour in pinniped breeding groups have not usually considered the number of females per breeding group, which could influence the degree of aggressiveness. We compared female agonistic behaviour (open-mouth displays and bites) within two colonies with different breeding substrates (homogeneous, Punta Norte; heterogeneous, Pirámide) of South American sea lions using two methods: weighted means and general linear models. We found that both aggressive interaction rates were significantly affected by female density, which accounted for a greater proportion on the variability in bite rates than in open-mouth rates. Controlling for the number of females, we found with both methods that open-mouth rates were higher than bite rates within the Pirámide colony; however, no differences were found within the Punta Norte colony. In Pirámide, open-mouth rates could be used more often as threats to minimise the chances of more severe aggressions. The conclusion is that females vary their use of agonistic interactions in relation to their density in the colony with heterogeneous substrate, which may be related to the presence of limited numbers of tide pools that heightens competition for thermoregulatory resources.

Sexual harassment and female gregariousness in the South American sea lion, Otaria flavescens

“…Our results supported two predictions: (1) there was a negative relationship between female-male interactions experienced by each female and the breeding group size and (2) males that owned large breeding groups interacted with each of their females less frequently. There is evidence for a dilution effect also from previous studies (Cassini and Fernández-Juricic 2003;Fernández-Juricic and Cassini 2007). More females simply dilute male harassment.…”

The diet of harbour and grey seals around Britain: Examining the role of prey as a potential cause of harbour seal declines

“…For example, Fernández-Juricic and Cassini (2007) found an increase in the rate of agonistic interactions with density in female South American sea lions, and Krieber and Barrette (1984) found a positive relationship between the proportion of aggressive interactions leading to animals leaving a site and the density of seals at the site. For example, Fernández-Juricic and Cassini (2007) found an increase in the rate of agonistic interactions with density in female South American sea lions, and Krieber and Barrette (1984) found a positive relationship between the proportion of aggressive interactions leading to animals leaving a site and the density of seals at the site.…”

Comparison of behavioral patterns of South American sea lions between breeding and non-breeding seasons

“…These results may be associated with the mutual mother-pup recognition demonstrated in otariids (Insley et al 2003) and with the reproductive behavioral pattern of this species (Campagna 1985, Campagna & Le Boeuf 1988a, Fernández-Juricic & Cassini 2007. Females alternate foraging trips at sea with suckling periods ashore, and when they return, mother and offspring have to find each other among the individuals in the colony (Charrier et al 2009, Muñoz et al 2011.…”

“…Aggressive encounters between males are frequent and males who initiate interactions are usually the ones who hold territories (Gerber et al 2010). Males chase and bite other individuals as a strategy to monopolize females (Campagna 2002), raising the number of offspring via defense of mates (Campagna 1985, Fernández-Juricic & Cassini 2007. Harassment of females by males may also contribute to the increment of aggressive behavior during the BS.…”