.JPG)
Arnold
van den Burg, Netherlands Institute of Ecology, P.O. Box 40, 6666 ZG
Heteren, The Netherlands. A.vandenburg@nioo.knaw.nlEmbryo mortality can arise due to health problems caused by dietary deficiencies. In birds, such problems are easy to detect compared to mammals, as deceased embryos can be obtained from failed eggs. Failed eggs of wild birds often contain embryos which show anomalies that have been described for poultry as being caused by micronutrient (minerals, vitamins, some aminoacids) deficiencies. Also, the developmental ages at which elevated embryo mortality occurs indicate the involvement of micronutrient shortages. In sparrowhawks (Accipiter nisus), anomalies that indicate vitamin B2 (riboflavin) deficiency are especially common. Vitamin B2, a key enzymatic co-factor in metabolism, is produced by plants and has to be relayed through the food chain to become available for sparrowhawk reproduction. Vitamin B2 is water soluble and does not accumulate in vertebrates. Vitamin B2 levels of sparrowhawk prey, which are almost exclusively avian, may thus be limited. The vitamin B2 concentration in sparrowhawk eggs is three times lower compared to great tit (Parus major) eggs. In the latter, vitamin B2 values depend on forest vegetation: in deciduous forests concentrations are higher compared to coniferous forests. This difference may cause sparrowhawks in poor coniferous forests to fail to lay at all and therefore cause a low number of breeding pairs.
