Van Den Burg A.B. (2002) A comparison of nutrient allocation in eggs of Barn Owls Tyto alba and Eurasian Sparrowhawks Accipiter nisus. ARDEA 90 (2): 269-274

Avian eggs are subject to hatching failure, the extent of which varies among species. Eurasian Sparrowhawks show on average 10% less hatching failures than Barn Owls. The difference in hatching success between these species may, among others, originate from the amount of nutrients that each species invests per egg. To determine whether this hypothesis applies to Sparrowhawks and Barn Owls, the allocation of nutrients in failed eggs was measured in terms of egg size, and lipid and protein content. Based on body size, incubation time, and embryonic development pattern it was expected that Barn Owls invest more nutrients in each egg compared to Sparrowhawks. On average, Sparrowhawks invested equal amounts of lipids in all eggs irrespective of egg volume, while Barn Owls invested more lipids as egg volume increased (but less than Sparrowhawks). Based on both egg volume and lipid content, the quality of Barn Owl eggs was lower than the eggs of Sparrowhawks. Therefore, the difference in hatching success between these species may relate to differential nutrient allocation