Digestibility of prey by the white stork under experimental conditions/Kattohaikaran ravinnon sulavuus koeolosuhteissa

Food composition of the White Stork Ciconia ciconia has been widely studied by pellet analysis throughout Europe, but the effect of digestibility on pellet contents has remained unclear. We studied the effect of digestion on the composition of pellets (N = 480) under experimental conditions in Poznan Zoological Garden in 2004-2005. Twenty-four captive wild-born White Storks were fed mammals, birds, amphibians, fish, insects and earthworms. Only the remains of mammals, birds and insects were found in the regurgitated pellets. Bones were present in 13.1% of pellets. Three chosen osteological pellet components (skulls, mandibles and innominate bones) were analyzed to determine the amount of bone loss by digestion. The digestive efficiency was greater than 95%. Based on a literature review, we compared results of pellet analyses with methods not affected by digestion (direct observations and prey remains). The invertebrate : vertebrate ratio in the White Stork diet differed significantly between methods. Preybiomass rather than the number of prey items should be considered a better reflection of the diet. Kattohaikaran (Ciconia ciconia) ravintokoostumusta on Euroopassa tutkittu paljon oksennus- ja ulostepelletteja analysoimalla, mutta ravinnon sulavuuden vaikutus pellettien sisaltoon on huonosti tunnettu. Tutkimme pellettien (N = 480) koostumusta kokeellisesti Poznanin elaintarhassa 2004-2005. Ruokimme 24 luonnossa syntynytta, tarhattua kattohaikaraa nisakkailla, linnuilla, sammakkoelaimilla, kaloilla, hyonteisillajakastemadoilla. Oksennuspalloista loytyi vain nisakkaiden, lintujen ja hyonteisten jaanteita. Luita loytyi vain 13,1 % palloista. Selvitimme myos ruuansulatuksen vaikutusta luiden haviamiseen analysoimalla kolme luukomponenttia (kallot, leukaluut ja nimeamattomat luut); haviaminen ylitti 95 %. Lisaksi vertailimme julkaistujen pellettianalyysien tuloksia menetelmiin, joissa ruuansulatus ei vaikuta tuloksiin (suorathavainnotja saaliinjaanteet). Selkarangattomien ja -rankaisten suhde kattohaikaran ravinnossa vaihteli merkitsevasti menetelmien valilla. Ravinnon biomassa kuvannee ravintoa paremmin kuin syotyjen saalispartikkelien maara.