Food from dumps increases the reproductive value of last laid eggs in the White Stork Ciconia ciconia

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.

White Storks (Ciconia ciconia) at nest, Algeria

White Storks (Ciconia ciconia) at nest, Algeria (Ali Mehadji, flickr)

Costs of migratory decisions: A comparison across eight white stork populations

Flack, A., Fiedler, W., Blas, J., Pokrovsky, I., Kaatz, M., Mitropolsky, M., Aghababyan, K., Fakriadis, I., Makrigianni, E., Jerzak, L. and Azafzaf, H., Feltrup-Azafzaf, C., Rotics, S., Mokotjomela, T. M., Nathan, R. & Wikelski, M. 2016. Costs of migratory decisions: A comparison across eight white stork populations. Science Advances 2(1): p.e1500931. doi: 10.1126/sciadv.1500931 (Open Access)

Abstract:

Annual migratory movements can range from a few tens to thousands of kilometers, creating unique energetic requirements for each specific species and journey. Even within the same species, migration costs can vary largely because of flexible, opportunistic life history strategies. We uncover the large extent of variation in the lifetime migratory decisions of young white storks originating from eight populations. Not only did juvenile storks differ in their geographically distinct wintering locations, their diverse migration patterns also affected the amount of energy individuals invested for locomotion during the first months of their life. Overwintering in areas with higher human population reduced the stork’s overall energy expenditure because of shorter daily foraging trips, closer wintering grounds, or a complete suppression of migration. Because migrants can change ecological processes in several distinct communities simultaneously, understanding their life history decisions helps not only to protect migratory species but also to conserve stable ecosystems.

Migratory behavior of juveniles from eight different White Stork populations

Fig. 1. Migratory behavior of juveniles from eight different White Stork populations (Flack et al. 2016)