Prey preparation by adult Great Tits Parus major feeding nestlings

Some birds prepare food items before giving them to their nestlings, We studied the relationships between the degree of prey preparation and prey size, nestling age, brood size and time of season, We estimated the degree of preparation of 513 animal prey items, taken by using neck collars, brought to nestling Great Tits Parus major. Prey preparation increased with prey size and decreased as the nestlings grew older, as brood size increased and as the season progressed, Other factors, such as nutrient concentration (through removal of low-quality or deleterious parts) or palatability (considering scaly moth forewings unpalatable), seem also to be important in determining prey preparation, Our results suggest that the degree of prey preparation is a compromise between the benefits gained by the nestlings (ingestion and digestion of prey is facilitated) and the costs to the parents (mainly time allocated to prey preparation).