[media; cf. attacks on whale calves] The kelp gull Larus dominicanus is an abundant and highly successful avian predator and scavenger that breeds along the coastline in the Southern Hemisphere, ranging from Antarctica to the tropics. On account of its dietary breadth, wide-ranging foraging strategies, and acclimation to modified landscapes, this species has received considerable attention within the seabird literature over the past 40 years. Furthermore, owing to its ready habituation to human-dominated environments, the species has been used as a bio-indicator of habitat modification.
Here we describe new predatory behaviors of the kelp gull on a larger-bodied sympatric mammal species, the Cape fur seal Arctocephalus pusillus pusillus, along the coast of Namibia, and discuss our findings as they relate to food web dynamics and behavioral plasticity.
[Keywords: food webs, generalist, plasticity, trophic interactions]
…The general pattern of predation occurred as follows: kelp gulls within the seal colony at Pelican Point individually approached both newborn seal pups that were wandering or lost from their mothers, as well as juvenile seals that were sleeping (Figure 2A). A single kelp gull then rapidly attacked the ocular region of the seal with its beak, and attempted to remove and consume the seals’ eyeballs (Figure 2B). Consumption of the eyeball signified a full, completed attack, which occurred roughly 50% of the time (total number of observations of attacks on apparently healthy seals was estimated at 500 over 15 years).
Successful, completed attacks generally lasted two minutes, and resulted in continued consumption (often joined by other gulls) of the body, leading to the death of the seal.
Consumption was focused on the soft and exposed dermal regions of the seals (underbelly, anus), and gulls used their beaks to puncture these areas. Partial attacks occurred when a gull did not consume the eyeball on the first attempt and the seal escaped, sometimes with the assistance of a nearby conspecific (eg. the conspecific would try to bite the attacking gull).
Given the distance of the observer from the seal colony, it was not possible to pursue these individuals and track their fitness. Hundreds of seal carcasses can be found year-round on the beach, including pups, juveniles and adults that have had their eyes removed (likely post-mortem, Figure 2C), although information is not available on the differences in attack rates according to size classes of seals. Furthermore, the cause of death of any particular carcass at Pelican Point could not be determined; due to the opportunistic nature of these observations, we can comment only on the behaviors themselves.
To our knowledge, this is the first record of this behavior in kelp gulls, suggesting that it may be unique to our study area.
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