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Density, nest site characteristics and breeding rates of the osprey (Pandion haliaetus) in the southern limit of its range in the Western Palearctic (Boa Vista, Cape Verde Islands)
Abstract
Between 2004 and 2007, we studied density, habitat features and breeding parameters of the osprey (Pandion haliaetus) population in Boa Vista Island (Cape Verde). A total of 79 nest structures were identified, 37 of which were occupied for at least 1 year during the study period. The osprey population ranged between 14 and 18 pairs, and the mean density and distance between neighbouring occupied nests were 2.58 pairs per 100 km2 and 3089 m, respectively. Occupied nests were found to be significantly further from the coastline and roads than unoccupied nests, but the distances from villages were similar. The majority (81.1%) of the 37 occupied nests were easily accessible to humans. Mean clutch size was 2.59, average productivity was 0.76 young/active nest, and breeding success was 58.8% [Correction added on 13 May 2013, after first online publication: the average productivity was changed from 0.72 to 0.76]. Density in Boa Vista was higher than that in other sedentary island populations in the Western Palearctic, whereas the productivity was the lowest of this region. Clutch size did not vary among Western Palearctic populations, but the differences observed in productivity were likely influenced by local factors that in Boa Vista are attributed to nest depredation by the brown-necked raven (Corvus ruficollis) and to direct human persecution.
... Currently, coastal insular ecosystems are highly threatened by climate change, introduction of exotic species or human pressure (Graci and Dodds, 2010;Hernández-Delgado, 2015;Spatz et al., 2017). In the Cabo Verde Islands, despite the ongoing development of the tourism industry, ospreys are still relatively common and widely distributed throughout the archipelago (Palma et al., 2019;Siverio et al., 2014). However, under the current increasing human pressure (López-Guzmán et al., 2013), vulnerable speciesparticularly top predatorssuffer disturbances during breeding and foraging (Siverio et al., 2014). ...
... In the Cabo Verde Islands, despite the ongoing development of the tourism industry, ospreys are still relatively common and widely distributed throughout the archipelago (Palma et al., 2019;Siverio et al., 2014). However, under the current increasing human pressure (López-Guzmán et al., 2013), vulnerable speciesparticularly top predatorssuffer disturbances during breeding and foraging (Siverio et al., 2014). Thus, ospreys (and other wildlife) should be closely monitored to detect early changes in population trends and new threats, and to design management actions (Salafsky et al., 2019). ...
... We collected data during the 2019-2022 nesting seasons within the framework of a long-term study (Siverio et al., 2014). During 2019-2022, the number of osprey breeding territories ranged between 18 and 22. ...
The use of anthropogenic debris as nest-building materials may affect nest function. We study ospreys (Pandion haliaetus) on an island with scarce vegetation and high availability of beached marine debris. We describe the anthropogenic debris in osprey nests, evaluate the factors affecting its prevalence and abundance, and test its potential effects on breeding parameters. We also quantify plastic entanglements among adults and nestlings. Of the 36 studied nests, 92 % included non-natural items, with plastic being the most frequent material (88.9 %). Nests that were bigger and closer to the coast had more anthropogenic items. The abundance of anthropogenic items in nests did not correlate with osprey breeding parameters. We recorded two live entangled adult females, which represent 3.9 % of the adult population. Monitoring the abundance of anthropogenic debris and its effects on wildlife is necessary to guarantee long-term viability of coastal wildlife.
... After 1999, ospreys were surveyed in Boavista in 2001-2002, with an estimate of 10-14 pairs (López-Suárez 2012), and in 2004-2007 when the number of breeding pairs grew from 14 to 17 (Siverio et al. 2013). A partial shoreline survey was also undertaken in 2003 (Ontiveros 2003). ...
... To update the osprey status in the country we reviewed all available post-2000 information, including publications (Ontiveros 2003, Siverio et al. 2013, theses (Fortes 2016) and the unpublished yearly monitoring reports of BIOS.CV and 'Projecto Biodiversidade'. Otherwise, surveys were undertaken by the authors in islands lacking recent information with the purpose of checking the species current distribution and numbers, as described below. ...
... On the opposite sense goes the growing impact of disturbance from tourism-related activities upon coastal nest sites on Boavista and Sal that jointly hold almost 30% of Cabo Verde ospreys (Palma et al. 2004, Siverio et al. 2013. That often results in breeding failure and is gradually causing the withdrawal of nest sites away from the coastline, undoubtedly a major concern for the species conservation (Palma et al. 2004, Siverio et al. 2013. ...
The first countrywide census of the osprey Pandion haliaetus breeding population in the Cabo Verde Islands took place from December 1997 to September 2001. Since then, about 20 years have elapsed without a new full assessment of the species situation in the country. Yet, some studies and monitoring work have been done in various islands, especially from 2016 onwards. Most notably, long-term monitoring has been carried out on the island of Boavista, recently followed by similar annual surveys on Sal. Although not covering the whole archipelago adequately, data currently available are sufficiently robust for allowing a reliable update of the species situation throughout most of its range and evincing its evolution since the turn of the century. The number of osprey pairs increased remarkably across most of the northern islands, which contain the large majority of the breeding population, while there are apparent signs of some recovery in the southern islands. This growth has presumably resulted from the gradual abandonment of the human harvesting of eggs and nestlings, a formerly widespread practice up to the mid-20th century that has now become rare. The osprey breeding population in Cabo Verde is currently estimated at about 115 pairs, showing an increase of over 30% in the last 20 years.
... En general, estos valores fueron mayores en Andalucía, intermedios en Islas Baleares y más bajos en Canarias, si bien el tamaño de las muestras en este último archipiélago para el éxito reproductor y tasa de vuelo solo fue de dos parejas. No obstante, al compararlos con los de las poblaciones de norte de Europa se advierte que son inferiores, aunque, por otro lado, son parecidos a los de la región mediterránea (véase Siverio et al., 2014). Tabla 17. Parámetros demográficos de la población de águila pescadora en España (2018). ...
... El pequeño tamaño muestral obtenido en 2018 para calcular los parámetros reproductores sugiere que los resultados, lejos de usarse como valores de referencia, deben ser tomados con mucha cautela a la hora de comparar con los de otras poblaciones. Ahora bien, si a dicha muestra se le añade la obtenida en 2013, 2014 y 2015 (Trujillo, 2014a;2014b;, años con un tamaño de población igual al de 2018 ( (Siverio et al., 2014). En tal caso, es posible que los pollos que vuelan en Canarias no sean suficientes para que la población se mantenga estable o que aumente (véase Evolución de la población). ...
Osprey Pandion haliaetus breeding population in Portugal (2018)
Palma, L. y Safara, J. 2018. Censo de la población reproductora de guincho o águila pescadora en Portugal en 2018. En, M. Siverio, F. Siverio, B. Rodríguez y J. C. del Moral (Eds.): El águila pescadora en España y Portugal: población invernante 2016-2017, reproductora en 2018 y método de censo, pp. 35-38. SEO/BirdLife. Madrid.
... En general, estos valores fueron mayores en Andalucía, intermedios en Islas Baleares y más bajos en Canarias, si bien el tamaño de las muestras en este último archipiélago para el éxito reproductor y tasa de vuelo solo fue de dos parejas. No obstante, al compararlos con los de las poblaciones de norte de Europa se advierte que son inferiores, aunque, por otro lado, son parecidos a los de la región mediterránea (véase Siverio et al., 2014). Tabla 17. Parámetros demográficos de la población de águila pescadora en España (2018). ...
... El pequeño tamaño muestral obtenido en 2018 para calcular los parámetros reproductores sugiere que los resultados, lejos de usarse como valores de referencia, deben ser tomados con mucha cautela a la hora de comparar con los de otras poblaciones. Ahora bien, si a dicha muestra se le añade la obtenida en 2013, 2014 y 2015 (Trujillo, 2014a;2014b;, años con un tamaño de población igual al de 2018 ( (Siverio et al., 2014). En tal caso, es posible que los pollos que vuelan en Canarias no sean suficientes para que la población se mantenga estable o que aumente (véase Evolución de la población). ...
... El promedio de huevos por nido que registramos es superior a los tres que reporta Kenyon (1947) y al promedio de 2.6 reportado por Siverio et al. (2014). Al parecer, el tamaño de la nidada tiene que ver con la latitud más que con la disponibilidad de alimento (Poole 1982). ...
Bird reproduction can be limited by the lack of nesting sites. At La Pinta estuary, Puerto Peñasco, Sonora, two species, the Osprey (Pandion haliaetus), and the Burrowing Owl (Athene cunicularia), had no nesting records in the area. We built seven artificial nesting structures to promote local reproduction, four saguaro shaped metallic posts for the Osprey, and three 60x60x60 cm concrete boxes for the Burrowing Owl. During eight reproductive seasons, between 2006 and 2013, we monitored the nesting structures from observation points 100 m away. Ospreys nested in at least one structure during the full period, except in 2012. In the study we recorded 17 nests with 55 hatching eggs, of which 53 produced fledglings in artificial sahuaros and power line poles. In 2005 a Burrowing Owl pair nested in a box laying seven eggs, and a pair nested in a natural burrow laying six eggs. Five and six chicks hatched, respectively. During the following five seasons owls were absent from the area, coming back in 2012, when we recorded a pair with four hatching eggs. In 2013, we observed five owl pairs, with 24 eggs, and 19 hatchlings, with an average of 4.8 eggs/nest. The nesting alternatives for the ospreys were the power towers and the artificial saguaros, nesting preferably en the artificial saguaros. The borrowing owls had as alternatives natural and man-made cavities, five out of eight pairs chose the natural cavities.
... Distance to the nearest breeding conspecific was another important factor influencing nest use probability in our study area, which was expected because roughlegged hawk is a territorial species and a given breeding pair can have more than one nesting structure within their territory (Mindell, 1983;Bechard and Swem, 2002). Food availability (Korpimäki, 1992;Terraube et al., 2012;Therrien et al., 2014a), intraspecific nest spacing (Krüger, 2004;Brambilla et al., 2006), weather (Bionda and Brambilla, 2012;Lehikoinen et al., 2013;Anctil et al., 2014) and nest site physical characteristics (Negro and Hiraldo, 1993;Siverio et al., 2014) have previously been related to nest use and reproductive output in raptors. ...
... El promedio de huevos por nido que registramos es superior a los tres que reporta Kenyon (1947) y al promedio de 2.6 reportado por Siverio et al. (2014). Al parecer, el tamaño de la nidada tiene que ver con la latitud más que con la disponibilidad de alimento (Poole 1982). ...
La reproducción en aves puede estar limitada por la ausencia de sitios de anidación. En el estero La Pinta, Puerto Peñasco, Sonora, no existían registros de reproducción del gavilán pescador (Pandion haliaetus) ni del tecolote llanero (Athene cunicularia). Construimos siete nidos artificiales con cuatro estructuras metálicas en forma de sahuaro para el gavilán pescador y tres cajones de concreto de 60x60x60 cm para el tecolote; esto con el fin de promover su reproducción. Durante ocho temporadas, entre 2006 y 2013, realizamos observaciones desde puntos a 100 m de las estructuras artificiales. El gavilán pescador anidó en al menos una estructura artificial en siete de las ocho temporadas. Durante el estudio registramos 17 nidos con 55 huevos, de los cuales 53 llegaron a volantones en sahuaros artificiales y postes de tendido eléctrico. Una pareja de tecolote llanero anidó en 2006 en una estructura artificial con una nidada de seis huevos, y otra lo hizo en una oquedad natural con una nidada de siete huevos; cinco y seis pollos eclosionaron, respectivamente. Durante las cinco temporadas siguientes estuvieron ausentes en el área; regresaron en 2012 y registramos una pareja con cuatro huevos, todos eclosionaron. En 2013, observamos cinco parejas de tecolotes, cuatro anidando en oquedades naturales y una en una estructura artificial; tuvieron una nidada total de 24 huevos: eclosionaron 19 pollos. El promedio de huevos por pareja fue de 4.8 para esta especie. Las alternativas de los gavilanes pescadores para anidar en el área de estudio fueron los postes de tendido eléctrico y los sahuaros artificiales; en este estudio, anidaron preferentemente en los sahuaros artificiales. Los tecolotes llaneros tuvieron como alternativas las oquedades naturales y las artificiales; cinco de las ocho parejas registradas seleccionaron las naturales.
Ospreys (Pandion haliaetus) are adaptable fish-eating raptors that readily nest on artificial structures in heavily human-dominated areas. Although the Osprey is a well-studied species, few researchers have investigated the factors that influence nest success and productivity in an urban environment. We monitored Osprey nests from 2013 to 2017 in highly urbanized Pinellas County, located on the west coast of central Florida, USA. We used logistic exposure models to assess the effects of timing of nesting, nest attributes (nest substrate, height), and landscape-level variables (inter-nest distance, distance to water, and surrounding habitat type) on daily survival rate (DSR) of Osprey nests. The number of active nests (i.e., nests with eggs) in the study area ranged from 53 in 2013 to 79 in 2016, with an overall total of 329 during the 5-yr study. Although most nests produced at least one young near fledging age, 131 of the nests failed. We attributed 45% of nest failures to storm events and 50% to unknown causes. The best logistic exposure model specification included only two variables: the discrete variable representing the date incubation started and the nominal variable indicating the year 2015. Osprey nests initiated earlier in the season were more likely to survive, and later nests (initiated after 22 April) averaged only one fledgling each. Osprey nests in 2015 had the highest DSR and relatively few failed due to storms. Our results supported previous research indicating that early nesters were more successful than late nesters. Our results also indicate that storms may play a role in nest success of Ospreys in Florida. Other variables, such as the amount of urbanized land surrounding Osprey nests did not appear to influence nest survival, indicating that Ospreys can be productive even in highly urban environments.
One enduring priority for ecologists has been to understand the cause(s) of variation in reproductive effort among species and localities. Avian clutch size generally increases with increasing latitude, both within and across species, but the mechanism(s) driving that pattern continue to generate hypotheses and debate. In 1961, a Ph.D. student at Oxford University, N. Philip Ashmole, proposed the influential hypothesis that clutch size varies in direct proportion to the seasonality of resources available to a population. Ashmole's hypothesis has been widely cited and discussed in the ecological literature. However, misinterpretation and confusion has been common regarding the mechanism that underlies Ashmole's hypothesis and the testable predictions it generates. We review the development of well‐known hypotheses to explain clutch size variation with an emphasis on Ashmole's hypothesis. We then discuss and clarify sources of confusion about Ashmole's hypothesis in the literature, summarise existing evidence in support and refutation of the hypothesis, and suggest some under‐utilised and novel approaches to test Ashmole's hypothesis and gain an improved understanding of the mechanisms responsible for variation in avian clutch size and fecundity, and life‐history evolution in general.
Physical characteristics of nest sites are thought to influence their use by birds and the outcome of breeding attempts. The presence of preexisting nesting structures can also be an important factor influencing reuse patterns and reproductive success. We examined the relationships between nest-site physical characteristics, patterns of nest reuse, and reproductive output in Rough-legged Hawks (Buteo lagopus) breeding in the Canadian High Arctic. Because this species is a rodent specialist, we also examined the effect of variation in lemming density, their primary prey, on reproductive output. We monitored 109 nesting attempts over a 9 yr period and sampled physical characteristics of 87 known nesting sites in 53 territories on Bylot Island, Nunavut, Canada. The probability that a nest was used by a breeding pair increased with the distance to the nearest breeding conspecific, for nests sheltered by an overhang, and with lemming density. Hawk nests inaccessible to foxes and facing away from the north were associated with high reproductive success. Reproductive success was also positively related to summer lemming density and negatively related to rainfall. Our results suggest that nest-site physical characteristics that offer a favorable microclimate and protection from weather and predators provide the highest-quality sites. We observed a high level of reuse of preexisting nests and previously occupied territories, which is indicative of site fidelity by individuals. Hawks that bred in a newly built nest had similar clutch size and hatching date compared to those that used preexisting nests, which suggests that building a new nest entailed no short-term reproductive costs. Reproductive success was nonetheless reduced for birds breeding in new nests located in newly occupied territories compared to those nesting in previously occupied ones, which suggests that a high proportion of pairs in new territories were young birds or that some of these sites were of low quality.
In 1998 and 1999, we carried out a systematic survey of the Osprey (Pandion haliaetus) in the Cape Verde Islands, to evaluate its population and conservation status. Some poorly surveyed areas were revisited in the summer of 2001 to complete our status assessment. We found an estimated 72-81 pairs on the archipelago, of which 94% were concentrated in the northern Barlavento (windward) islands group. In this area the species is common and seems to be recovering from a presumed decline, probably caused by a long-term overharvesting of eggs and nestlings by humans during past decades. On the contrary, in the southern Sotavento (leeward) islands the species is currently scarce, seemingly still on the decline and already extirpated in the southwesternmost islands. The high percentage of abandoned near-shore nests in the eastern ''flat'' islands is probably associated with the increasing tourism activities. ESTADO ACTUAL DEL A ´ GUILA PESCADORA PANDION HALIAETUS EN LAS ISLAS DE CABO VERDE RESUMEN.-Durante el año 1998 y la primavera de 1999 se hizo una prospección sistemática del a ´guila pescadora (Pandion haliaetus) en las islas de Cabo Verde con la intención de actualizar la información sobre su estado poblacional y de conservación. Algunas a ´reas peor prospectadas fueran visitadas en el verano de 2001 para confirmar datos anteriores. Se obtuvo como estimación más probable el nú mero de 72-81 parejas reproductoras en todo el archipiélago, largamente (94%) concentradas en el grupo de islas septentrionales del Barlavento. En este a ´rea, la especie es bastante común y parece estar recu-perándose de un presunto declive durante las décadas pasadas, como resultado probable de un contínuo expolio de huevos y pollos para la alimentación humana. Al contrario, en las islas del grupo sureño del Sotavento, la especie es actualmente muy escasa y sigue aparentemente en declive y incluso ya extinguida en las islas del extremo suroccidental. El incremento del turismo costero constituye una amenaza adi-cional para los nú cleos poblacionales de las islas ''llanas'' orientales al echar la especie de sus sitios vulnerables de nidificación costera, como lo indica el alto porcentaje de nidos abandonados a lo largo del litoral. [Traducción de los autores]
The paper presents data on the current status of the Osprey and the White-tailed Sea Eagle populations in the northwestern part of the Vologda region and southeastern Onego area. Field trips and studies at permanent plots done between 1988 and 2005 have demonstrated that the study area is inhabited by a uniform population of the White-tailed Sea Eagle, the main distinctive feature of which is the tendency to form compact settlements on the shores of large bodies of water in the forest zone. Its total abundance is ca. 100 pairs. About a third of the population (30-35 pairs) lives on the Rybinsk impoundment reservoir in the Darwin strict nature reserve, forming the largest source from which birds apparently dispersed to other large lakes of the region in the 1980s-1990s. Our estimate of the total Osprey population in the Vologda Lake District and southeastern Onego area is 150-180 breeding pairs, of which 50-55 nest in the Darwin reserve and its buffer zone. Expeditions outside the area in question have shown that the population density of the species decreases towards all directions, their abundance being limited to occasional pairs. It is demonstrated that this source area with high abundance of the White-tailed Sea Eagle and the Osprey formed as the populations in the Darwin reserve increased in density in the 1950s-1970s. After that the species spread to lakes and reservoirs of the Vologda Lake District and southeastern Onego area, where the natural habitats are similar.
Nearly all European Osprey (Pandion haliaetus) populations have had a similar fate during the 20th century. In the first two decades, if not earlier, dramatic decreases and even extirpations of many local populations occurred due to heavy persecution. There was then a recovery period until the second decrease from the 1950s to the mid-1970s, caused by DDT and other contaminants. Since then, populations have been recovering. The annual rates of population increase have varied from about 1% in Fennoscandia to about 10% in Scotland during the last 20 years. At present, 90% of all European Ospreys breed in Finland, Sweden and Russia. The nesting habitats vary widely from steep cliffs in the Mediterranean to closed climax coniferous forests, open peat bogs and large clear-cut areas in northern Europe. In some areas (e.g., Finland), cutting of old, flat-topped potential new nests by intensive commercial forestry has been the most important national threat for the local Osprey population during the last three decades. As early as the late 1960s dedicated bird banders started to construct artificial nests for Ospreys to compensate for the losses caused by one-track forestry. In 1995, 46% of all occupied Finnish Osprey nests (N = 951) were artificial. Also, clear-cuts around nesting trees are harmful because nests become more exposed to storms, predation by Eagle Owls (Bubo bubo) and disturbances. In Finland and some other countries, new guidelines for foresters also account for the welfare of the Osprey. However, the principles and practices are still quite far from each other.
Ospreys (Pandion haliaetus) declined throughout the Great Lakes basin during the 1950s to 1970s due to usage of organochlorine pesticides. Following the banning of DDT in 1972, artificial elevated nest structures were erected in the Kawartha Lakes region of south-central Ontario to aid in their recovery. As the population grew, large stumps of flooded trees, < 1 m above the surface of the water became important nesting sites, despite their propensity to flood in turbulent weather conditions. We compared the productivity of Ospreys among nest substrates and longevity of the nests in this area from 1991 to 2001. Of 260 individual nesting attempts made over the 11 years, 57% used man-made structures, primarily either quadrupod nesting platforms or utility poles. Of nests on natural substrates, stump nests accounted for 37% of total nesting attempts; elevated tree nests were relatively uncommon (6%). Productivity of stump nests was significantly greater than that of artificial or tree nests (1.48 versus 1.16 and 0.73 chicks produced per occupied nest, respectively). Nevertheless, survivorship of stump nests was less than that of platform nests after 3 years of age, as high water levels, storms or winter ice activity destroyed some of these low nests between breeding seasons. Ospreys were able to attain greater productivity in these stump nests than on man-made nesting substrates.
As a regular breeding species in Central Europe the osprey is presently confined to the Federal States of Mecklenburg-Vorpommern and Brandenburg in eastern Germany, and Pomerania and Mazuria in Poland. This is probably due to human persecution, especially in earlier decades. In Mecklenburg the population reached its lowest level with only 37 pairs in the DDT-period between 1968 and 1972. In Brandenburg, a slow but steady increase has occurred, from ca. 45-50 pairs in the early 1980s to over 120 pairs today. There has probably been a relationship between contamination with pesticides, reproductive success and population development which, however, has been very poorly studied. One limiting factor for the osprey population may have been the scarcity of suitable trees for nesting. The species prefers the tops of isolated old trees or trees on the edge of the forest dominating the adjacent trees. Due to forestry, such trees have become increasingly rare to the point that only a small fraction of the osprey population can nowadays reproduce in the traditional way. Fortunately, ospreys started to breed on power lines as early as 1938. On the pylons the nests are apparently safer than in trees. Nowadays over 75% of ospreys nest on these artificial structures in Germany, although no such breeding is known in Poland. This important adaptation may have helped the species to recover. The breeding success of 258 tree-nests and 366 nests on power-lines was studied. While the tree-nesting population remained rather stable, the pylon nesters strongly increased. On average, pylon-nesting ospreys produced more young than tree-nesting ospreys
El Águila Pescadora se encuentra En Peligro Crítico 1 por tener una población muy pequeña (2001-2002) de unas 30-38 parejas repartidas en dos núcleos aislados (archipiélagos balear y canario).Alo largo de las décadas de los años sesenta, setenta y principios de los ochenta, sufrió una drástica disminución en sendas subpoblaciones, habiendo desaparecido como reproductor de las costas levantinas y andaluzas. A pesar de haber mostrado una recuperación importante en las últimas décadas, sus efectivos se consideran demasiado exiguos, probablemente muy cercanos al límite de la capacidad de acogida del hábitat, siendo por ello muy incierta su viabilidad.
Breeding population size and some reproductive aspects of Osprey Pandion haliaetus in La Gomera and El Hierro (Canary Islands) were studied during the 2003 and 2004 breeding seasons. All active nests were situated in the southern coasts of both islands. A total of five territorial pairs were detected in La Gomera and one in El Hierro, nesting three in La Gomera and one in El Hierro. These islands contain about 30% of the entire Canarian Osprey population and 16-17% of the Spanish population. Laying dates, estimated in ten day periods, were 21-31 March (n=3) and 1-10 May (n=2). Mean productivity (0.86) was lower than that estimated by some authors for stable populations. Human activities such as recreational sailing, trekking or camping near the nests could limit the establishment of new pairs and cause low productivity.
MANY ornithologists have noted declines in Osprey (Pandion haliatus carolinensis) populations in the United States since the beginning of the twentieth century (Bent, 1937; Stone, 1937; Kenyon, 1947; Ames and Mersereau, 1964; Schmid, 1966; and others). The acceleration of these declines in the last 15 to 20 years is causing much concern among conservationists. It is axiomatic that, assuming no permanent emigration, a decline in population size results from (1) increased mortality, (2) decreased productivity, or (3) a combination of both of these. This paper reports on estimates of mortality rates derived from reports of band recoveries from a segment of the northeastern population of Ospreys banded in New York and New Jersey from 1926 to 1961. Although these estimates do not necessarily reflect the mortality rates now being sustained by this population, they show the amount of production per nest needed to maintain the population and bring into focus the dynamics of the decline that has taken place.
We studied the diet of breeding Ospreys (Pandion haliaetus) in the Cape Verde archipelago during 2006, using prey remains recovered at 21 nests and perches on the islands of São Vicente, Santiago, Santa Luzia, Boavista, Branco, and Raso. We identified a total of 1264 individual fish prey items of 35 species. Diet was dominated (>80%) by only six fish species, including Trachinotus ovatus, Exocoetus volitans, Aulostomus strigosus, Sparisoma cretense, Sardinella maderensis, and Tylosurus acus. Dominant prey species varied among islands, but diet similarity was greater between nearby islands. Pelagic species were consumed most frequently (>60%) in Boavista and Santa Luzia, whereas demersal reef fish dominated (>50%) in the other islands. The fish consumed were generally large, though there was wide variation in estimated length (20.7–62.2 cm) and weight (49–1117 g). A comparison of Osprey diet with Cape Verde fisheries suggested that the potential for conflict is low, due to minimal overlap in the primary species caught. Changes in marine productivity associated with the ongoing moderate warming of the Canary Current System may represent a threat, though there is considerable uncertainty about the type and magnitude of these effects. Monitoring of Osprey numbers, breeding success, and diet is required to detect any changes associated with availability of food sources, and such monitoring may also provide a relatively simple and inexpensive method to track long-term changes in littoral fish assemblages.
The paper reports on the breeding biology of the endemic subspecies of the Grey Wagtail in a human transformed area (banana plantations) on Tenerife (Canary Islands). Clutch size (3.96 ± 0.6) was lower than in continental zones, probably because of the climatic stability of the islands. Furthermore, the distance from the nest to the nearest water source and the length of the breeding season (late February-June) were greater than in other European populations. Some breeding traits fit the predictions of the so-called insular "syndrome". Possible mechanisms underpinning these differences in breeding traits are discussed.
We studied the diet of the osprey Pandion haliaetus in the Canary Islands during 1997-2008 using prey remains under perches and nests, and direct observations. We collected data both in breeding territories and in non-breeding areas. We counted a minimum of 307 fish individuals as prey remains (both during breeding and non-breeding seasons), and identified another 78 during 433 hours of field observations. According to our results, ospreys consumed at least 15 taxa belonging to 12 families. We found slight differences in the spatial (both intra and inter insular) and temporal diet composition. During the breeding season, the main prey species were flying fishes (belonging to the family Exocoetidae) and needlefishes (belonging to the family Belonidae) according to the two employed methods (i.e. prey remains and direct observations). In the non-breeding period, the diet was composed primarily of non-autochthones freshwater fishes such as common carp Cyprinus carpio and goldfish Carassius auratus. In general, the diet diversity was similar to the diversity reported in other breeding populations of subtropical areas, and being less diverse than those of tropical areas. More precise studies evaluating the effect of fish availability in marine reserves, overfishing areas or fish farms on the demographic parameters are necessary for the management and conservation of threatened Canarian ospreys.
The feeding behaviour of the Osprey Pandion haliaetus was studied at feeding grounds, feeding perches and nests in the Clarence Valley, north-east New South Wales, from 1991 to 1996. Foraging behaviour was found to be similar to that of Northern Hemisphere birds. Although birds were found to take mostly living fish, one record of possible scavenging was made. The male Osprey was the main provider during the breeding season, bringing food to the nest for the female and nestlings. Details of hunting, delivery of food to the nest area, eating behaviour, courtship feeding, food solicitation, and interspecific competition are presented.
We studied the nest site selection and distribution pattern at landscape level of the German Osprey population, and demonstrated
how to test the predictions of the ideal free distribution theory and its derivatives on such an expanding population. Information
about the location and breeding success of each Osprey nest site between 1995 and 2005 was collected through a long-term monitoring
programme. Data of land cover types were acquired from the administrations of each federal state and the CORINE Land Cover
database. The results showed that Ospreys preferred landscapes with more water bodies and forests. Such sites were also occupied
earlier and had higher local population density. However, in the study period of 11years, there was a gradual shift from
forest-dominated landscapes to agricultural land-dominated landscapes. The breeding success increased over time, with no difference
in the breeding success between pairs nesting on trees and poles, whereas there was higher breeding success at nest sites
surrounded by more agricultural land and less forest. The more efficient foraging in eutrophic lakes in agricultural landscapes
was the most likely cause for the higher breeding success. The distribution pattern of the Ospreys did not match the resource
allocation, which deviated from the models tested. We suggested that the proximate cues used for nest site selection mismatched
site quality due to anthropogenic environmental changes.
We analyzed geographic variation in laying date, clutch size, and number of fledglings in the common kestrel Falco tinnunculus in the Western Palearctic. We also examined whether breeding parameters of some island-dwelling kestrels differed in latitude, with special reference to Tenerife Island. General Linear Models were applied. The mean laying date (LD, mean 30 April) correlated positively with latitude, with a delay of 6 days for every 10 ºN. The mean clutch size (CS, mean 4.95 ± 0.26) increased significantly with latitude and was affected by nest-type (nest-box vs natural nests). The mean number of fledglings showed no correlation. Tenerife populations nesting below 1,000 m.a.s.l. showed the earliest LD in the Western Palearctic while those nesting above 1,000 m.a.s.l. showed a similar nesting pattern to European populations, although the CS is lower. The latitudinal variation in LD and CS coincides with the classical postulates (delay and increase respectively, towards the North) but does not explain the variations presented here. In agreement with recent studies, nest-type (nest-box vs natural nests) and climatic factors such as temperature (winter, spring) and spring rainfall influence latitudinal variations. Data from Tenerife are consistent with the hypotheses of delayed breeding associated with altitude and reduced CS in island birds.
The osprey (Pandion haliaetus) population nesting along the lower portion of the Columbia River (river mile 29 to 286) increased from 94 in 1997 to 103 occupied nests in 1998 (9.6% annual rate of increase) to 225 occupied nests in 2004 (13.9% annual rate of increase). The more recent rate of population increase was associated with higher reproductive rates than in 1997/1998, and significantly lower egg concentrations of most organochlorine (OC) pesticides, polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). A comparison of observed egg residue concentrations in 2004 with effect-level information for ospreys indicated that reproduction at few, if any, nests was adversely affected. As recent as 1997/1998, dichlorodiphenyldichloroethylene (DDE) was still adversely affecting reproductive success for a portion of this population. Mercury was the only contaminant evaluated in both 1997/1998 and 2004 that showed a significant increase in eggs over time, but concentrations in 2004 (0.09 microg g(-1) ww) remained below established effect levels for birds (generally reported at 0.50 microg g(-1) ww or higher). The significant increase in mercury justifies the need for future monitoring. All contaminants mentioned that biomagnify up food chains can be effectively monitored in osprey eggs. The osprey has been shown to be an excellent sentinel species for long-term monitoring with their many useful traits described.
Ospreys, Pandion haliaetus, started breeding in continental France (Loiret) in the mid 1980s. In 1999, a national recovery plan for the conservation of this species was initiated. The conservation efforts, especially building artificial nests where natural nests or trees holding nests had fallen down, favoured and sped-up the colonisation of new sites, resulting in to 18 known breeding pairs in 2003, confirming the installation of a small population in central France. A capture-mark-recapture research program (R. WAHL) enabled us to describe the breeding phenology and to estimate key demographic parameters for this population. Since 1995, 152 fledglings have been ringed as well as a few adults. Each breeding pair produced an average of 2 fledglings per year, yet the number of fledglings varied between sites and increased with the size of the colonies. Individuals were highly philopatric, with nearly all breeding adults coming back to breed the following year, and about, 40% of the chicks fledged returning to breed in the study area. Age at first breeding was 3.2 ± 0.4 years for females, and 4.4 ± 1.8 years for males. Recapture probability was high and averaged 0.913. Adult survival probabilities were high and were lower for younger breeding females (0.870 ± 0.098, IC95%: 0.551 - 0.973) than for older females and males (0.971 ± 0.036, IC95%: 0.737 - 0.997). Survival probability during the first year of life was 0,512 ± 0.156 (IC95%: 0.236 - 0.781). A matrix population model with four age classes was built to model the dynamics of this population. The population growth rate estimated with environmental stochasticity (1.245) indicated that the population should continue to increase in the near future. Although the high survival, breeding success and early age at first breeding could partly explain the increase of the population size, the rate of increase estimated by the population model remained lower than the observed rate of increase (1.643). The immigration of individuals, particularly from eastern parts of Germany, could help explain this difference.
Island biogeography is the study of the distribution and dynamics of species in island environments. Due to their isolation from more widespread continental species, islands are ideal places for unique species to evolve, but they are also places of concentrated extinction. Not surprisingly, they are widely studied by ecologists, conservationists and evolutionary biologists alike. There is no other recent textbook devoted solely to island biogeography, and a synthesis of the many recent advances is now overdue. This second edition builds on the success and reputation of the first, documenting the recent advances in this exciting field and explaining how islands have been used as natural laboratories in developing and testing ecological and evolutionary theories. In addition, the book describes the main processes of island formation, development and eventual demise, and explains the relevance of island environmental history to island biogeography. The authors demonstrate the huge significance of islands as hotspots of biodiversity, and as places from which disproportionate numbers of species have been extinguished by human action in historical time. Many island species are today threatened with extinction, and this work examines both the chief threats to their persistence and some of the mitigation measures that can be put in play with conservation strategies tailored to islands.
Breeding diurnal raptors on the island of Corsica are compared to those of other mainland areas. At the level of the community, they do not show insular characteristics, although, at the level of the population, it appears that some species - mainly forest species - maintain endemic characters, high density, expansion of habitat-range, and particular breeding characteristics.
Where possible, human activity near nesting Pandion haliaetus should be minimized and not initiated after ospreys have commenced nesting. Logging operations should be designed to minimize disruption of nesting ospreys, possibly by delaying operations in the area until young have fledged. -from Authors
An Osprey (Pandion haliaetus) population nesting in the vicinity of Cascade Reservoir in west-central Idaho was studied for three years. The area supported about 50 nesting pairs, which laid an average of 2.58 eggs and fledged an average of 1.37 young per active nest throughout the study. These productivity estimates suggest a healthy, increasing population. Most nests were atop snags (66%) and on private land (70%). Ospreys nesting on artificial sites and those nesting more than 1,500 m from human disturbances produced more offspring. Fish in the 11-30 cm range constituted the bulk of the diet (89%) with brown bullheads being the most important prey species (38%). Osprey captures reflected prey availability. Establishment of Cascade Reservoir increased the availability of fish, which, in turn, allowed the Osprey population to increase. Productivity of these hawks appears to be chiefly related to reservoir level and prey availability.
Food taken by Ospreys (Pandion haliaetus) was assessed at nine nests in the Clarence Valley, in northeastern New South Wales, from 1991 to 1996 by observing food taken to nests and collecting remains below nests. Opportunistic observations and collections were also made at other nests and feeding sites on the north coast of New South Wales. The diet consisted primarily of mullet species, particularly the Sea Mullet (Mugil cephalus), and Yellowfin Bream (Acanthopagrus australis). The diet differed from that of Ospreys in the Great Barrier Reef, but was similar to that in other subtropical and tropical areas of the world.
This study reports on aspects of the breeding biology of Ospreys (Pandion haliaetus) on Kangaroo Island from data collected over 18 breeding seasons between 1985 and 2004. Over this period an average of nine pairs were located each year, and a total of 145 occupied territory years were monitored for breeding activity and outcomes. Of these, active breeding occurred in 103 ( 71%), with 60% of these successfully fledging young. Productivity was found to average 0.66 young fledged per year per occupied territory, and 0.92 young fledged per year per active nest. This level of productivity, while similar to that of other studies in Australia, is below the minimum recruitment levels needed to maintain migratory Osprey populations in the northern hemisphere. However, such high rates may not be needed in the non-migratory population of Australia. Although some early dispersal was recorded among marked Osprey young, strong philopatric recruitment was also evident, with 22% of survivors either remaining on the island, or returning at maturity to join the breeding population. Through the re-identification of individuals, Osprey pairs were found to remain together over many seasons and to use the same primary nesting site. The breeding season began later than reported elsewhere in Australia, extending from August to February, with most laying occurring in September. Undetected nest predation and human disturbance was suspected at accessible nests as contributing to the high level of nest failures recorded. The apparent elongated nestling development period found is comparable to that determined in other studies where fluctuating prey availability directly influenced nestling growth and survival. These factors, plus geographical isolation, suggest the Osprey may be precariously balanced ecologically at the southern extent of its breeding range in Australia.
In 1998 and 1999, we carried out a systematic survey of the Osprey (Pandion haliaetus )i nthe Cape Verde Islands, to evaluate its population and conservation status. Some poorly surveyed areas were revisited in the summer of 2001 to complete our status assessment. We found an estimated 72-81 pairs on the archipelago, of which 94% were concentrated in the northern Barlavento (windward) islands group. In this area the species is common and seems to be recovering from a presumed decline, probably caused by a long-term overharvesting of eggs and nestlings by humans during past decades. On the contrary, in the southern Sotavento (leeward) islands the species is currently scarce, seemingly still on the decline and already extirpated in the southwesternmost islands. The high percentage of abandoned near-shore nests in the eastern ''flat'' islands is probably associated with the increasing tourism activities.
Historically the non-migratory Osprey (Pandion haliaetus) population at the Ojo de Liebre and Guerrero Negro Lagoons, in Baja California Sur, Mexico, was confined to three small islands. In response to the addition of channel markers, electrical and utility poles and many human-made structures in and around the Lagoons during the 1950s, the Ospreys began nesting on suitable artificial structures. Nesting on artificial structures in- creased Osprey reproductive success, which caused an increase in Osprey numbers, and the structures themselves influenced nesting distributions. Now, nearly 50% of the Ospreys in the area nest on artificial structures in and around both Lagoons.
that populations are regulated during the winter months when resources are scarce; clutch size is determined by the resources available during the breeding season relative to population density. Hence, the greater the seasonal fluctuation in resources, the larger the average clutch size. Lati- tudinal variation in clutch size and the relative uniformity of clutch size among species within areas are consistent with Ashmole's hypothesis. The hypothesis is tested indirectly in this paper by relating clutch size to seasonal variation in actual evapotranspiration (AE), which is propor- tional to primary production. Clutch size is directly related to the ratio between summer AE and winter AE. In addition, clutch size is inversely related to winter AE, but it is independent of summer AE. These results are consistent with the hypothesis that the number of breeding indi- viduals is regulated in winter and that population size exerts a density-dependent influence on resources available to each individual for reproduction. To demonstrate further the relation be- tween population density and reproductive rate, clutch size is shown to be directly related to the ratio between summer productivity and the density of breeding adults. Moreover, clutch size is inversely related to population density, but it is not related to production during the breeding season. This analysis suggests that geographical trends in clutch size are caused primarily by factors that limit populations during the nonreproductive period rather than by the abundance of resources during the breeding season. Received 26 February 1979, accepted 18 August 1979. VARIATION among populations of birds in the number of eggs per nest (clutch size) has preoccupied evolutionary ecologists since David Lack (1947, 1948) first discussed the subject in detail. Lack suggested that the characteristic clutch size of each species should correspond to the number of young that parents can nourish adequately. Within this constraint, birds should rear the largest number of young possible so as to maximize their individual fitness. Lack's ideas about food limitation and fitness have been elaborated by numerous refinements, including optimization of reproductive effort with respect to life expectancy (Williams 1966, Gadgil and Bossert 1970, Cody 1971, Charnov and Krebs 1974, Goodman 1974) and habitat stability (Cody t966, MacArthur and Wilson 1967), adjustment of parental feeding effort in accordance with the level of clutch-size-dependent predation (Skutch 1949), antipredator adaptations (Ricklefs 1970), overlap of breeding and molting seasons (Foster 1974), variation among species in the energy requirements of young (Royama 1969), and the relationship of the breeding season to the spring flush of insects (Slagsvoid 1975). But as yet, ecologists have not reached a concensus about the relative importance of these factors. The single most striking pattern of variation in clutch size, by which all hypotheses about clutch size are ultimately tested, is the direct relation between clutch size and latitude. To account for this trend, Ashmole (1961, 1963) outlined a simple hypoth- esis based upon seasonality of resources. He suggested that reproductive rate should depend upon both resource level and population density during the breeding season. If populations were limited by resources during the nonbreeding season, the level of resources available in the breeding season relative to population density would
Ospreys (Pandion haliaetus) have been the focus of conservation efforts since their dramatic population decline attributed to dichlorodiphenyltrichloroethane and related chemicals in the 1960s. Several recent studies of ospreys nesting in the United States have indicated improved reproduction. However, the density of breeding ospreys varies greatly among locations, with some areas seemingly habitable but not occupied. Because of concerns about pollution in the highly industrialized portions of the Delaware River and Bay, USA, we evaluated contaminant exposure and productivity in ospreys nesting on the Delaware River and Bay in 2002. We characterized habitat in the coastal zone of Delaware, USA, and the area around the river in Pennsylvania, USA, using data we collected as well as extant information provided by state and federal sources. We characterized habitat based on locations of occupied osprey nests in Delaware and Pennsylvania. We evaluated water clarity, water depth, land use and land cover, nest availability, and contaminants in sediment for use in a nest-occupancy model. Our results demonstrated that the presence of occupied nests was associated with water depth, water clarity, distance to an occupied osprey nest, and presence of urban land use, whereas a companion study demonstrated that hatching success was associated with the principal components derived from organochlorine-contaminant concentrations in osprey eggs (total polychlorinated biphenyls, p,p′-dichlorodiphenylethylene, chlordane and metabolites, and heptachlor epoxide). Our study provides guidelines for resource managers and local conservation organizations in management of ospreys and in development of habitat models that are appropriate for other piscivorous and marsh-nesting birds.
Scavenging raptors have been postulated to be declining at a rate far higher than predatory raptors. To test this hypothesis we reviewed the historical and present status of the seven raptor species—three scavengers (two kites and a vulture), one partial scavenger (a buzzard) and three species (osprey and two falcons) that take live prey—that breed on the Cape Verde islands. Scavenging raptors have experienced steeper declines and more local extinctions than non-scavengers in Cape Verde, with the partial scavenger midway between the two groups. Causes of scavenger decline include incidental poisoning, direct persecution and declines in the availability of carcasses and other detritus. These findings, which highlight the conservation importance of the island of Santo Antão, indicate the priority that needs to be accorded to scavengers, particularly in Europe where many insular populations are reaching unsustainable levels.
Sequential habitat occupation and productivity of Ospreys Pandion haliaetus were studied in the recovering Estonian population from 1985 to 1999. During this period, the number of known nests increased from five to 32. Nest-sites closer to the foraging grounds and with more lakes nearby were occupied first and had the highest productivity. Through a reduction in the quality of sites available, the average productivity of Ospreys decreased as their numbers rose, consistent with despotic distribution models. The sites occupied first during the recolonization were also those that had been the last to be abandoned during the population's decline prior to 1980. However, newcomers preferred sites near established pairs. Therefore, conspecific attraction explained some stochasticity left unexplained by deterministic resource models.
The breeding biology of the Red Kite Milvus milvus is still little known in the southern part of its range (Mediterranean), despite recent conservation concerns and major declines in most insular populations (Sicily, Sardinia and Balearics). We report here on the breeding biology of the Red Kite in Corsica in 1996–99 and on recent population trends there. In a 42-km2 study area located in the northwest of the island (Balagne region), breeding density was locally high (1.17–1.78 breeding pairs/km2). Breeding dispersion ranged from loosely colonial to dispersed, with average nearest-neighbour distance of 444 ± 316 m (range 50–2000) (all data as means ± sd). Kites established breeding territories in January–February, and 92.4% of territorial pairs laid a clutch (n = 238). Laying took place between February and May (mean lay date: 27 March ± 16 days, n = 147). Clutch size averaged 2.44 ± 0.71 (1–5 eggs, n = 96), hatching success 66.9% and fledging success 78.6%. Productivity averaged 1.33 ± 0.88 young per breeding attempt (n = 221) and 1.65 ± 0.65 young per successful breeding attempt (n = 173). Overall breeding success was 51.4 ± 38.0% (n = 88). We describe the growth of young (wing, weight, tarsus and bill) and show a marked seasonal decline in clutch size and breeding performance, with pairs laying earlier producing larger clutches and being more successful than later breeding pairs. Unlike most other insular Mediterranean Red Kite populations that have recently declined, the breeding population in the northwest of Corsica, which accounts for c. 25% of the whole island population, increased from 25 to 35 pairs in 1989 to a maximum of 80–90 pairs in 1997. This increase was probably related to the lack of persecution and a local increase in abundance of Rabbits Oryctolagus cuniculus, following their introduction in the late 1970s, which provided an important feeding resource for Kites. Finally, we compare our results with those from other Red Kite populations studied in Europe. We found that there is a latitudinal gradient in laying date and productivity across Western Europe populations, but no evidence of an insular syndrome in the Corsican population.
An important issue in population ecology is to disentangle different density-dependent mechanisms that may limit or regulate animal populations. This goal is further complicated when studying long-lived species for which experimental approaches are not feasible, in whose cases density-dependence hypotheses are tested using long-term monitored populations. Here we respond to some criticisms and identify additional problems associated with these kinds of observational studies. Current caveats are related to the temporal and spatial scales covered by population monitoring data, which may question its suitability for density-dependence tests, and to statistical flaws such as the incorrect control for confounding variables, low statistical power, the distribution of demographic variables, the interpretation of spurious correlations, and the often used stepwise series of univariate analyses. Generalised linear mixed models are recommended over other more traditional approaches, since they help to solve the above statistical problems and, more importantly, allow to properly test several hypotheses simultaneously. Finally, several management actions aimed to recover endangered species, such as supplementary feeding, might be considered as field experiments for further testing density-dependence hypotheses in long-lived study models. We expect these opportunities, together with the most adequate statistical tools now available, will help to better our understanding of density-dependent effects in wild populations.
Monitoring natural populations is often a necessary step to establish the conservation status of species and to help improve management decisions. Nevertheless, many monitoring programs do not effectively address primary sources of variability in monitoring data, which ultimately may limit the utility of monitoring in identifying declines and improving management. To illustrate the importance of taking into account detectability and spatial variation, we used a recently proposed estimator of abundance (superpopulation estimator) to estimate population size of and number of young produced by the Snail Kite (Rostrhamus sociabilis plumbeus) in Florida. During the last decade, primary recovery targets set by the U.S. Fish and Wildlife Service for the Snail Kite that were based on deficient monitoring programs (i.e., uncorrected counts) were close to being met (by simply increasing search effort during count surveys). During that same period, the Snail Kite population declined dramatically (by 55% from 1997 to 2005) and the number of young decreased by 70% between 1992-1998 and 1999-2005. Our results provide a strong practical case in favor of the argument that investing a sufficient amount of time and resources into designing and implementing monitoring programs that carefully address detectability and spatial variation is critical for the conservation of endangered species.
After a general profile of the country, information is given concerning the history of leprosy in the Cape Verde Islands, with data related to the control activities of the years 1950-77. Finally the authors present the data collected during the first 2 years of activities under the new National Leprosy Control Project.
1. Understanding how density-dependent and independent processes influence demographic parameters, and hence regulate population size, is fundamental within population ecology. We investigated density dependence in growth rate and fecundity in a recovering population of a semicolonial raptor, the osprey Pandion haliaetus [Linnaeus, 1758], using 31 years of count and demographic data in Corsica. 2. The study population increased from three pairs in 1974 to an average of 22 pairs in the late 1990s, with two distinct phases during the recovery (increase followed by stability) and contrasted trends in breeding parameters in each phase. 3. We show density dependence in population growth rate in the second phase, indicating that the stabilized population was regulated. We also show density dependence in productivity (fledging success between years and hatching success within years). 4. Using long-term data on behavioural interactions at nest sites, and on diet and fish provisioning rate, we evaluated two possible mechanisms of density dependence in productivity, food depletion and behavioural interference. 5. As density increased, both provisioning rate and the size of prey increased, contrary to predictions of a food-depletion mechanism. In the time series, a reduction in fledging success coincided with an increase in the number of non-breeders. Hatching success decreased with increasing local density and frequency of interactions with conspecifics, suggesting that behavioural interference was influencing hatching success. 6. Our study shows that, taking into account the role of non-breeders, in particular in species or populations where there are many floaters and where competition for nest sites is intense, can improve our understanding of density-dependent processes and help conservation actions.
Monitoring and conservation of Finnish Osprey Pandion haliaetus in 1971–2005 In: Status of Raptor Population in Eastern
- P Saurola
- P Saurola
Die bestandsentwicklung des Fischadlers Pandion haliaetus in Deutschland im ausgehenden 20
- D Schmidt
Schmidt, D. (2001) Die bestandsentwicklung des Fischadlers
Pandion haliaetus in Deutschland im ausgehenden 20.
Jahrhundert. Vogelwelt 122, 117-128.
Sytuacja Rybołowa Pandion haliaetus w polsce na pocza z tku XXI wieku
- T Mizera
Mizera, T. (2009) Sytuacja Rybołowa Pandion haliaetus w polsce
na pocza z tku XXI wieku. Stud. Mater. CEPL 22, 45-55.