Zoological Studies

Seasonal Changes in the Avian Diet of Breeding Sparrowhawks Accipiter nisus: How to Fulfill the Offspring’s Food Demands?

Małgorzata Bujoczek and Michał Ciach (2009) During the 2002-2006 breeding seasons, changes in the diet of Sparrowhawks Accipiter nisus were studied in the Carpathian Mountains (southeastern Poland).  Material (1592 prey items) from 4 periods of the breeding cycle was analyzed.  Among 61 identified bird taxa, Turdus philomelos, Sylvia atricapilla, T. merula, Fringilla coelebs, Erithacus rubecula, and Parus major dominated and comprised 41% of the total number of prey.  Turdus merula, T. philomelos, and Garrulus glandarius comprised 42% of the total biomass.  Prey items varied in weight from 5 to 485 g.  Typical prey of Sparrowhawk males (≤ 35 g) dominated, and their proportion in the diet increased from 55% to 77% during the breeding season.  Typical prey of females (> 120 g) were caught to a greater extent (21%) in the 1st period only, and their proportions (to 2%) of the diet significantly decreased in the next periods.  With respect to the total biomass, large birds dominated in the 1st period only (54%).  The percentage of small- and medium-sized birds in the total biomass increased as the season progressed.  In successive periods of the breeding season, the ratio of the number of prey to its biomass significantly increased.  Despite females resuming hunting activities in the nestling and post-fledgling periods, there was no increase in the mean body weight of avian prey supplied to the young.  However, there was a marked increase in the number of prey items found at the nest.  It was concluded that with the high food demands of the rapidly growing Sparrowhawk nestlings, it is more efficient to more-frequently catch small birds than to less-frequently catch larger birds.  This might decreases the parents’ time and/or energy expenditures for feeding nestlings.