Interspecific kleptoparasitism by Brown-headed Gulls (Chroicocephalus maculipennis) on two hosts with different foraging strategies: a comparative approach

Abstract

Kleptoparasitism is a well known foraging strategy used opportunistically by many seabirds. Our study compares the strategies performed by a facultative kleptoparasite species, the Brown-hooded Gull (Chroicocephalus maculipennis), associated with two hosts with different foraging strategies, the American Oystercatcher (Haematopus palliatus) and Red-gartered Coot (Fulica armillata). In total, 97% of the prey items stolen from Oystercatchers were the clam Tagelus plebeius, and all prey items stolen from Coots were the crab Cyrtograpsus angulatus. The attack rate by Gulls (number of kleptoparasitic attacks per unit time) did not differ significantly between Oystercatchers and Coots, but the success rate of attacks (successful kleptoparasitic attacks as a proportion of total attacks) was greater for attacks on Coots than on Oystercatchers. The mean rate of feeding (number of stolen items ingested per minute) by Brown-hooded Gulls did not differ with host. Gulls strongly selected large prey when stealing food. The comparison of net intake (cost—benefit balance) for each kleptoparasite—host system showed that profitability was 3.5 times higher when kelptoparsitising Coots than when stealing from Oystercatchers. We suggest future work should study in more detail the costs and benefits for kleptoparasites with multiple hosts in similar systems elsewhere.

Additional keywords:

• facultative kleptoparasite
• foraging strategy