An improved type of wire cage for the study of parental feeding behaviour in hole-nesting passerines

Several techniques have been used to record details of feeding ecology in altricial birds. However, they often fail to provide the number, identity and size of prey, and/or the relative contribution of males and females. We designed and tested a handmade wire cage for filming nests in nest boxes (or natural holes) that allowed us to accurately (1) determine the sex and relative contribution of each parent and (2) identify each prey item and its size in a Great Tit Parus major population. The sex of adults was recorded successfully for all entries into the nest. The rate at which parents brought food and prey sizes were within the range obtained with other techniques in the same area. None of the nests were deserted and no detrimental effects on chick weight were found. A number of advantages compared to a previous design are discussed.