Stork Population Research Articles

Nesting of the black stork ( Ciconia nigra) and white-tailed eagle ( Haliaeetus albicilla) in relation to forest management

Since 1957, 200 m zones around known nests of the black stork ( Ciconia nigra) and white-tailed eagle ( Haliaeetus albicilla) have been strictly protected in Estonia. Yet, the black stork population has recently suffered a large decline, which coincides with the intensification of forestry. To check whether higher disturbance levels could have caused the decline, we related the extent of forestry operations and mature forest near black stork nests to their occupancy, treating the increasing eagle population as a comparison. For both species, we studied 1 km zone around 38 nest sites and, for each nest site, around two random points 2 km away. The total annually cut and reforested area was used to quantify forestry activity, since this single variable explained most of the variability in the extent of different forestry operations. Management was significantly more extensive in the landscapes inhabited by black storks than those inhabited by white-tailed eagles, but the periods of nest occupancy and unoccupancy did not differ significantly in either species. There were neither species-specific nor occupancy-related differences in the total area of mature forest. We conclude that, compared with the white-tailed eagle, the black stork is more vulnerable to disturbance and landscape change due to forestry operations, but these processes are probably not responsible for the recent decline of the stork population.

Chaunocephalus ferox in free-living white storks in central Spain.

Ten out of 42 (23.8%) white storks (Ciconia ciconia) admitted to two rehabilitation centers in central Spain had lesions caused by the trematode Chaunocephalus ferox in the small intestinal wall. Fourteen of the examined birds were adults, five were subadults, and 23 were chicks of various ages. Parasitation was 32% (n = 8) in chicks and 13% (n = 2) in adult birds, whereas no juvenile bird was affected. Among dead birds, stork chicks affected by C. ferox lesions had a lower body weight (2196.1 g, SD = 814.2) than storks without lesions (2965.8 g, SD = 742.9, P < 0.05). Two chicks were additionally infected with Salmonella subspecies I serotype enteritidis 1,9,12: g, m:1, 7. Prevalence of the parasite in the examined birds was lower than in a population of Asian open-billed storks (Anastomus oscitans), in which it was pathogenic due to the destruction of the tunica muscularis and formation of large granulomatous lesions in the wall of the postduodenal portion of the small intestine. Pathogenic alterations caused by C. ferox are presumed to be related to numbers of adults present. Because storks admitted to rehabilitation centers suffer stress due to various reasons that may lower their immune response and exacerbate existing infections, the analysis of fecal sediments of white storks admitted for rehabilitation is recommended.

The role of birds in the ecology of West Nile virus in Europe and Africa.

Surveys on wild birds conducted during the last two decades in Europe, notably Poland and the Czech Republic, to determine their infection rate with WN virus have revealed endemic foci of infection. Some species of seropositive birds were nonmigrators while others were hatchlings of migrating species. Persistently infected avian reservoirs are potential sources of viruses for mosquitoes that multiply in the temperate European zone in hot, wet summers. In the past, evidence for geographical circulation of WN viruses was based on antigenic analysis of strains from different countries while more recent epidemiological studies have relied on analysis of nucleotide sequences of the envelope gene. With the reappearance of epidemic WN fever in European countries, interest has been focused once again on the African origin of the causal agent carried by migrating wild birds. In some epidemics, isolates were made from human cases or mosquitoes and only serologic evidence for infection was available from domestic and wild bird populations. In this respect the unusual findings of anti-WN virus antibodies in a population of storks maintained in northern Germany could be interpreted as evidence for local infection. The unique susceptibility of young domestic geese in Israel in 1997-2000 to WN virus and the isolation of similar strains from migrating White storks in Israel and Egypt suggest that the recent isolates are more pathogenic for certain avain species and that migrating birds do play a crucial role in geographical spread of the virus. Knowledge of the routes taken by birds migrating between Africa and Europe will therefore help in selecting sites where attempts to isolate viruses will be most fruitful. The appearance of the disease in western European equine populations (Italy and France) requires that other birds and their migratory routes be investigated once more. It remains to be determined whether the European endemic foci of WN virus are in themselves sources of infection for other birds that migrate across Europe and do not necessarily reach sub-Saharan Africa. If this is the case it will be necessary to define the strategies for detection of virus overwintering in the European temperate climate.

Genetic variability and level of differentiation among Brazilian pantanal wood stork populations.

The Wood Stork (Mycteria americana) is a colonial wading bird of the tropical and lower subtropical zones. We assessed genetic structure within and among five stork colonies from the Brazilian Pantanal and compared our data with those from North American populations. Samples of 234 individuals were studied using protein electrophoresis to evaluate genetic variability and interpopulation differentiation. Of 22 loci examined, 7 were polymorphic (mean heterozygosity = 0.068). The low Fst value (0.005) indicated little intraspecific variation among breeding colonies. Estimated number of migrants per generation based on private alleles (Nm = 11.3) and on Fst (48.8) suggests high gene flow Nei's genetic distance values among Pantanal colonies ranged from 0.0001 to 0.0034, demonstrating low genetic divergence among populations. Our data can be explained by supposing high gene flow levels among Pantanal colonies, and between North and South American populations, intermediated by a probable interbreeding population in Central America.

Foraging ecology of the endangered wood stork recorded in the stable isotope signature of feathers.

Down feathers and regurgitant were collected from nestling wood storks (Mycteria americana) from two inland and two coastal breeding colonies in Georgia. The stable isotopic ratios of carbon (13C/12C) and nitrogen (15N/14N) in these materials were analyzed to gain insights into the natal origins of juvenile storks and the foraging activities of adults. Down feathers differed in δ13C between inland and coastal colonies, having average isotopic values that reflected the sources of carbon fixed in biomass at the base of the food web. Feathers from the inland colonies differed between colonies in δ15N, while those from the coastal colonies did not. These patterns primarily reflected the foraging activities of parent storks, with individuals capturing differing percentages of prey of distinct trophic status at each colony. Collectively, the carbon and nitrogen isotopic signatures of feather keratin were used to distinguish nestlings from each colony, except for instances where storks from different colonies foraged in common wetlands. The stable isotopic composition of food items in regurgitant was used to reconstruct the trophic structure of the ecosystems in which wood storks foraged. Predicted foraging activities based on the isotopic composition of keratin were generally consistent with the percentage of prey types (freshwater vs. saltwater and lower trophic level vs. upper trophic level consumer) observed in regurgitant, except for the coastal colony at St. Simons Island, where the δ13C of feathers strongly suggested that freshwater prey were a significant component of the diet. This inconsistency was resolved by aerial tracking of adults during foraging excursions using a fixed-wing aircraft. Observed foraging activities supported interpretations based on the stable isotope content of feathers, suggesting that the latter provided a better record of overall foraging activity than regurgitant analysis alone. Observed foraging patterns were compared to the predictions of a statistical model that determined habitat utilization based on habitat availability using a geographic information system (GIS) database. Observed foraging activities and those predicted from feathers both suggested that some adult storks preferred to feed their young freshwater prey, even when saltwater resources were more accessible in the local environment. This conclusion supports the contention that wood stork populations are sensitive to changes in the distribution of freshwater habitats along the southeastern coastal plain of the United States.

Storks Deliver Babies (p= 0.008)

This article shows that a highly statistically significant correlation exists between stork populations and human birth rates across Europe.While storks may not deliver babies, unthinking interpretation of correlation and p‐values can certainly deliver unreliable conclusions.

Low Levels of Genetic Variability in North American Populations of the Wood Stork (Mycteria americana)

The breeding population of Wood Storks (Mycteria americana) in the southeastern United States has declined since the 1930s, resulting in the listing of all United States populations of the species as endangered in 1984. We assessed genetic structure within and among nine colonies of Wood Storks from Georgia and Florida. Levels of band sharing based on multilocus oligonucleotide DNA fingerprinting of individuals from seven colonies ranged from 58% among nests within the same tree to approximately 55% within the same colony. Levels of band sharing were similar to those reported for other populations of birds that have experienced drastic reductions in population size. A more thorough analysis of four polymorphic microsatellite loci for 136 individuals from nine colonies indicated low levels of allelic diversity and low genetic divergence among colonies. Genetic differentiation (F ST = 0.015) was similar to levels detected from allozymes for 15 colonies of Wood Storks in Florida (F ST = 0.019). These data, together with demographic studies of these populations, indicated high levels of gene flow among colonies (N m = 16.4). In agreement with previous studies, we recommend that all colonies of Wood Storks in the southeastern United States be managed on a regional basis as a single interbreeding population. Similar genetic surveys of the disjunct breeding populations of Wood Storks in South America and Central America would be beneficial in understanding the total genetic differentiation in the species.

Geographical variation in the density of the white stork Ciconia ciconia in Spain: Influence of habitat structure and climate

The spatial variation in the density of white storks Ciconia ciconia in Spain is analysed with respect to landscape and meteorological variables. The density of breeding pairs in 1985 was negatively correlated with surface cover of woodlands and shrublands, and positively correlated with the area of dry or wet grasslands, reflecting food availability and foraging preferences of the storks. Average minimum temperature in April–May (the first few days after hatching) was also negatively correlated with stork density, and the reproductive success in a colony at El Tietar (Avila) was inversely correlated with the number of days with precipitation in May. The negative influence of minimum temperature and precipitation on breeding density appears to be linked with the mortality of recently born nestlings. Practical recommendations are made for the conservation of the Spanish population of white storks through incentive use of pastures, meadows and ‘dehesas’ for cattle grazing. Reintroduction efforts must be direct towards zones having large areas of these habitats, and mild weather.

The Importance of the Water Conservation Areas in the Everglades to the Endangered Wood Stork (Mycteria americana)

During 1985–1989, numbers of the endangered Wood Stork (Mycteria americana) in the Water Conservation Areas of the Everglades, Florida, showed an annual peak in February or March of 1233 to 7874 birds. The annual maxima are significantly greater in dry years than in wet years (P &lt; 0.05). Most storks are nonbreeders and are found foraging in open habitats along the eastern and southern parts of Conservation Area 1 and Conservation Area 2A and along the west‐central side of Conservation Area 3A. In dry years, large numbers move into the southern half of Conservation Area 3A. We estimated that in spring, the total southeastern United States population of Wood Storks is between 14,000 and 20,000 individuals. The annual maxima of the water conservation areas were at least 8% to 10% of the total southeastern U.S. population in wet years and possibly as much as 55% in dry years. The Water Conservation Areas appear to be critical foraging habitat for wintering storks, especially during drought years when most of the rest of south Florida is dry. Changes in the management of these areas could have a major impact on the status of storks throughout the southeastern United States.

Chaunocephalosis in a wild population of Asian open-billed storks in Thailand.

The most common trematode collected from Asian open-billed storks (Anastomus oscitans) was Chaunocephalus ferox (80% prevalence). The trematode was paired in granulomas in the intestinal wall. Based on histological examination of these capsules, there was degeneration and necrosis of muscle cells in the tunica muscularis. Granulation tissue with hetrophil and lymphocyte infiltration appeared in the granulomas. Intestinal villi were shorter and wider in infected areas than in non-infected areas. Some intestinal glands were dilated. Storks with high intensity of C. ferox appeared ill. The death of storks infected with C. ferox may result from malnutrition due to the loss of absorptive function of the intestine and from the effect of granuloma formation which might interfere with the intestinal peristalsis.

BREEDING STATUS OF THE BLACK STORK IN THE TRANSVAAL

Summary Tarboton, Warwick. 1982. Breeding status of the Black Stork in the Transvaal. Ostrich 53:151-156. Black Storks were censused in the Transvaal during 1976–81 at 40 breeding sites of which 38 were occupied during at least one of the survey years. The Transvaal Black Stork population was estimated to be 50–70 breeding pairs. The storks bred in winter on cliffs in the hilly parts of the Transvaal, laid 2–5 eggs ([xbar] = 3,37; n = 19) and reared 1–4 young ([xbar] = 2,27; n = 22). Productivity was 2,24 young/clutch laid (n = 37) or 1,38 young/pair-year (n = 60). Pairs failed to breed, on average, in 38% of the years, usually in years of below-average rainfall. In severe drought years as few as a quarter of the known pairs attempted to breed. Coincidentally, in drought years Black Stork numbers increased greatly in the eastern Lowveld (Kruger National Park) where permanent feeding habitat exists but breeding sites are scarce, and it is suggested that this area, and possibly the Limpopo River, provide im...

The distribution and abundance of marabou storks in Uganda*

SummaryA series of censuses throughout Uganda showed that the population of marabou storks between 1970 and 1972 was of the order of 4000–5000 of which the majority were usually in Ruwenzori (formerly Queen Elizabeth) National Park. There were at least twenty breeding colonies totalling some 1300 nests.Marabous have two main types of food. Firstly, there is what might be termed ‘natural food’, such as insects and amphibia, and the poachings from carcasses. This is assumed to have been the only kind of food available to marabous until comparatively recently. The other type is food obtained as a consequence of human activity. In Uganda, the second category is now far more important than the first.The numbers of marabous at three sites are considered in relation to their food supply, and in each case it appeared that there was usually an excess of food. Against this background, consideration is given to those factors which might be limiting to the rate of increase of this species.Marabous have obviously benefited from human activity and have no doubt increased greatly in numbers as a result. Moreover, they are probably still increasing, and it appears likely that they will continue to do so.

Marking of European Storks

ARRANGEMENTS that have been made to broadcast the progress of flights of storks marked with numbered rings at the ornithological stations at Rossitten and Essen in Germany, recall the history and results of bird-ringing in Europe, which commenced with the stork and have, perhaps, revealed most regarding the migrations of the white stork, Cicon—a alba. In 1710 a large bird, described as a heron or a stork, probably the latter, was captured in Germany and on its legs were several metal rings, one of which bore an inscription stating the bird had been caught in Turkey several years before. This is believed to be the first attempt at marking migrating birds with rings. A hundred years later Brugmann captured a few storks in Holland and placed rings on their legs, but failed to trace them. In 1899, Mortensen, in Denmark, succeeded in marking and recovering a number of birds, and after that the practice of ringing became very extensive. Two years later, Prof. Thienemann founded the Rossitten Ornithological Station on the Baltic shores, where bird marking has since been carried out on an extensive scale. 110,000-120,000 storks have been marked since 1917 in Denmark and one from Jutland is believed to be between thirty and forty years of age (Skovgaarde). At the same time, however, the stork population has been reported to be decreasing in Holland and elsewhere. 2,000 storks are estimated to inhabit Denmark, but France's nesting colonies have vanished and nests are rare in Italy and Russia, and the colonies in Alsace are vanishing. It has been stated (Bowen) that a pair built on the roof of St. Giles Cathedral, Edinburgh, in 1466, but did not return.