Differences between diet of adult and chick Audouin's Gulls Larus audouinii at the Chafarinas Islands, SW Mediterranean

Differences in diet between chicks and adu1ts of Audouin ' s Gu11 Larus audouinii were exarnined in fue Chafarinas Is1ands (SW Mediterranean) during fue breeding seasons of 1993 and 1994. The major food type for chicks on fue Chafarinas Is1ands were fish, both epipe1agic (some of them coming from purse-seine activity) and benthonic (coming from traw1er discards), forming a minimum 70 % by biomass. The amount of fish fed to young increased with chick age, up to 95 % by biomass. Adu1ts also consumed main1y fish (75 % by number and 90 % by biomass), most1y c1upeiforms, Sardina Sardina pil-chardus and Gi1t Sardine Sardinella aurita. Terrestrial prey were especia11y given to youngest chicks, probab1y because of requirements to increase fue feeding cates of fuese chicks. Shorter foraging trips to fue near Moroccan coast to feed on terrestria1 prey (chiefIy arthropods and isopods) may al10w adu1ts especia11y to guard/brood sma11 chicks, and eventua11y to increase fue feeding cates. Feeding cates significant1y decreased with brood size, and also decreased with chick age, although this effect was not significant. Weight and size of food items fed to chicks increased with chick age, and fledg1ings were fed with 1arger items than those consumed by adu1ts. This was probab1y re1ated to fue increase in gape width with chick age, and fue trade-off between food 10ad carried to ~ feed chicks and the distance trave1ed to catch fue fish...,