Djerdali, S., Guerrero-Casado, J. & Tortosa, F. S. (2016). Food from dumps increases the reproductive value of last laid eggs in the White Stork Ciconia ciconia. Bird Study 63: 107–114. doi: 10.1080/00063657.2015.1135305
Abstract:
Capsule: Accessing extra food from waste dumps increases egg volume and hatching mass in White Storks.
Aim: To test how White Storks vary their investment in egg size, especially in last laid eggs, in relation to food availability, and to improve our understanding of the importance of extra feeding on intra-clutch variation.
Methods: The study was carried out in three White Stork breeding colonies in northern Algeria. Breeding performance was recorded in 70 nests over three years. White Stork colonies situated close to chicken farms were considered to be part of a ‘pseudo experiment’ where parents had access to extra food. Egg volume, laying order, hatching order and hatching weight were recorded.
Results: Egg volume and hatching mass in White Storks was significantly greater when they had access to extra food. The reproductive value of last laid eggs (fourth and fifth) doubled when females had access to extra food.
Conclusion: Laying smaller last eggs within a clutch provides a mechanism to facilitate early brood reduction in the White Stork, and so should be advantageous when food is scarce. On the contrary, when females had access to extra food, last laid eggs were as big as first eggs which suggests egg size variation is adaptable to local conditions.
North African Birds 