The impact of village proximity on clutch size and nesting succes of starlings (Sturnus vulgaris Linnaeus 1758)

Abstract

Čvorak (Sturnus vulgaris) je široko rasprostranjena gnjezdarica kontinentalne Hrvatske, a nastanjuje i prirodna i urbana staništa. Cilj istraživanja bio je utvrditi eventualni utjecaj blizine naselja na veličinu pologa i uspješnost gniježđenja čvorka tijekom dva gniježđenja u proljeće 2015. godine na području sela Mokrice u Hrvatskom zagorju i okolne šume. Istraživana su gnijezda u škrinjicama. U svakoj škrinjici zabilježen je datum leženja prvog jaja, broj jaja, izmjerena je njihova duljina i širina te zabilježen broj izvaljenih mladunaca. Mjerenje jaja izvođeno je pomičnim mjerilom, a volumen je izračunat prema Hoytovoj formuli. Normalnost podataka testirana je Shapiro – Wilkovim testom, a u statističkoj analizi korištene su Pearsonova korelacija i ANOVA. Značajna razlika između parametara gniježđenja u selu i šumi zabilježena je samo kod broja jaja i broja mladunaca, pri čemu su u šumi dobivene više vrijednosti za obje varijable. Nije zabilježena negativna korelacija između volumena jaja i veličine pologa te nije potvrđena hipoteza ustupka. Veći broj jaja i mladunaca a time i veća uspješnost gniježđenja zabilježeni su u prvom pologu čime su potvrđena i ranija istraživanja o smanjenim reproduktivnim svojstvima čvoraka prilikom odmicanja sezone gniježđenja.Starling (Sturnus vulgaris) is a widespread nesting bird in continental Croatia inhabiting natural and urban habitats. The aim of this study was to determine the possible impact of the proximity of the settlement to their clutch size and nesting success during two nesting periods in the spring of 2015 conducted at the Mokrice village in Hrvatsko Zagorje region and surrounding woods. The study used nests located in nesting boxes recorded. The laying date of the first egg, number of eggs, egg length and width, as well as the number of hatched offspring were recorded for each nest. Calliper was used to measure the eggs and the volume was calculated according to the Hoyt formula. The normality of the data was tested by the Shapiro - Wilk test and the statistical data were calculated using Pearson correlation and the ANOVA. A significant correlation between the success of nesting in the village and the forest was found only in the number of eggs and the number of offspring, where the forest provided higher value for both variables. No correlation between the volume of eggs and the clutch size was found which have not confirmed trade-off hypothesis of optimal clutch/egg size. A larger number of eggs and offspring and a higher breeding success recorded in the first brood confirmed earlier findings about reduced reproductive characteristics of starling later in breeding season