Assessing diet composition of White Storks (Ciconia ciconia) breeding under North African conditions provides key information to understanding its trophic niche for conservation purpose. Since, climate controls productivities of foraging habitats and thus food availability for predators, this study examines how Storks’ diet parameters varied following a climate gradient along with rural-to-urban landscapes in north-eastern Algeria. Feeding strategies to cope with severe conditions were discussed in light of climate aridity and urbanization and how these influence reproduction, population dynamics and distribution. While invertebrate prey accounted for 94 % of ingested individuals, the biomass intake was dominated by chicken remains scavenged from rubbish dumps (67 %) and small mammals (14 %). Generalized linear models revealed that prey numbers varied significantly between climatic regions and landscapes types, but no significant differences were observed for other dietary parameters, including prey biomass. The study showed high dietary similarity between study climates and landscapes, mainly among rural and urban colonies located in semi-arid and sub-humid areas, which differed from those in suburban and arid climate. Rarefaction and extrapolation curves indicated that prey species richness in White Stork diets was expected to be higher in urban colonies located in sub-humid climate. Despite low prey species diversity in arid regions, the White Stork demonstrates a broad trophic niche, which could be due to supplementary feeding from human refuse. This study suggests that regardless of the climate or landscape, White Storks ensure a constant food intake, despite prey biomass fluctuations, by adapting their diet. Foraging in diverse habitats, including trash dumps, ensures a sufficiently balanced diet to meet nutritional requirements.

Variation in White Stork (Ciconia ciconia) diet along a climatic gradient and across rural-to-urban landscapes in North Africa.

In the present study, we evaluated the effect of distance to food from rubbish dumps and colony size on White Stork breeding success. Waste from poultry farms is expanding in the study area and is commonly used by the White Stork as a new food resource, which may explain the increase in the number of breeding Storks in the region. The study was carried out at 24 sites, including 88 different colonies of White Stork in northern Algeria, Setif (36°09′N, 05°26′E; 900 m.a.s.l.); over a 4-year period (2002–2005) with considerable variation in rainfall. Nests were monitored at different distances from 30 rubbish dumps emanating largely from chicken farms. Results of the General Linear Mixed Models (GLMM) showed that breeding success of White Stork was dependent upon distance to dumps, recording the highest values in nests close to these places with food supply. There was a highly significant interaction between the year and the distance to the rubbish dumps. That is, reproductive success was higher when there was extra food in all years except in 2002, which could be due to the very low rainfall during spring 2002. Also, we found a significant interaction between colony size and distance to a rubbish dump. Results suggest that White Stork breeding success was also affected by natural food resources, since bigger colonies may deplete natural prey sooner, which is more evident in dry years.

The effects of colony size interacting with extra food supply on the breeding success of the White Stork (Ciconia ciconia)

Survival and reproduction of young can be affected by growth parameters. It is thus important to estimate intraspecific growth rate variability and environmental factors affecting growth to better understand the dynamics of populations and the potential impacts of environmental changes. Growth parameters of White Stork (Ciconia ciconia) nestlings were estimated in eastern Algeria, in the southern part of the species’ range. A total of 2,756 measurements of 65 nestlings from 18 nests were taken for body mass, and tarsus, wing and bill lengths. Individual growth data were used to investigate the effects of nest occupation date, laying and hatching dates, clutch size, number of hatchlings, productivity, hatching order, and brood reduction on nestling growth patterns. Body mass and bill length growth rates were lower in the studied population than in a more northerly White Stork population. This supports the hypothesis of a geographic variation in intraspecific growth parameters. Chicks from nests occupied early reached higher asymptotic body mass but tended to grow more slowly. However, chicks from late arriving birds compensated for the difference in body mass and wing length by higher growth rates. Wing length was significantly affected by asynchrony and hatching order. Last hatched chicks had larger asymptotic wing lengths, lower wing growth rates and longer growth periods. Wings of nestlings from highly asynchronous broods grew faster but took more time to attain the inflection point. Brood reduction had a negative effect on nestling bill length at hatching. Chicks from nests with little brood reduction had a longer bill at hatching than nestlings from nests with high brood reduction.

Factors affecting growth parameters of White Stork nestlings in eastern Algeria

Assessing feeding conditions and variations of diet composition over the breeding season is of great help in the understanding of the ecological niche of species. In meeting this aim, the White Sto...

Trophic Niche and Feeding Strategy of the White Stork (Ciconia ciconia) during different Phases of the Breeding Season

Understanding factors influencing the nest site selection of birds in coastal cities is a major topic in urban ecology, with important management and conservation implications. We investigated the White Stork (WS, Ciconia ciconia) nest habitat use in the coastal city of Rabat, Morocco. We used data on a series of topographic, landscape, coloniality and spatial parameters to identify the best predictors of nest presence using generalized linear models. These variables were measured at nest supports (n = 107) and supports with no nests (n = 107) within 1.5 km radius landscape. The results showed a high probability of WS nest presence on a 4° slope, an exposition between 148 and 172 °N, elevation above 130 m, near roads, approximately 2300 m from the nearest river, from 5 to 28% agricultural areas, and a cover of villas with tall-trees higher than 60%. WS nest presence occurs also in buffers with more than 20 nests and those with less than 500 m between nest supports. Variation partitioning analysis revealed that the joint effect of landscape and coloniality (17%) and landscape, coloniality and space (17%) are important for nest site selection by WS. In Rabat, WS nests are mainly established in the villa zone with trees and also in the already occupied areas. These results will have important implications for the Rabat urban environmental managers in managing this coastal city while considering the needs of breeding storks.

Landscape and coloniality are robust predictors of White Stork nest habitat selection in a coastal urban environment

We studied variations in the size of breeding colonies and in breeding performance of White Storks Ciconia ciconia in 2006–2008 in north-east Algeria. Each colony site was characterized using 12 environmental variables describing the physical environment, land-cover categories, and human activities, and by three demographic parameters: the number of breeding pairs, the number of pairs with chicks, and the number of fledged chicks per pair. Generalized linear mixed models and the self-organizing map algorithm (SOM, neural network) were used to investigate effects of biotic, abiotic, and anthropogenic factors on demographic parameters and on their relationships. Numbers of breeding pairs and of pairs with chicks were affected by the same environmental factors, mainly anthropogenic, which differed from those affecting the number of fledged chicks per pair. Numbers of fledged chicks per pair was not affected by colony size or by the number of nests with chicks. The categorization of the environmental variables into natural and anthropogenic, in connection with demographic parameters, was relevant to detect factors explaining variation in colony size and breeding parameters. The SOM proved a relevant tool to help determine actual dynamics in White Stork colonies, and thus to support effective conservation decisions at a regional scale.

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Nawel Djeddou

Papers

Using self-organizing maps to investigate environmental factors regulating colony size and breeding success of the White Stork (Ciconia ciconia)