Driving forces behind the fluctuating growth of the number of successful nests in an inland population of white-tailed eagles in Hokkaido,Japan

This study aimed to describe the change in the number of successful nests of the white-tailed eagle, Haliaeetus albicilla, for 25 years (1997–2021) along the Teshio River (100 km), Japan, which is a new habitat for this endangered species and identify factors driving the number of nests. The number of nests grew from two to nine. The logistic function fitted in well with the growth, and the capacity of the study area sustaining the successful nests was estimated at 6.5. The precipitation in January and April explained the deviation of the observed values from the model prediction. In particular, heavy rain in April was associated with low numbers. Forty-six nest remains were collected from 17 nest locations. Twelve genera of birds, six genera of mammals, and four genera of fishes were identified. Fish and bird items occupied 93.6% of prey individuals. The fish proportion was similar between high-performance years when the observed number of successful nests was higher than the model prediction and low-performance years with a lower number than the prediction (55.2% and 51.0%). However, it was higher in the nests with two fledglings (63.0%) than those with a single fledgling (41.5%). The nearest neighbor distance (NND) of the successful nests declined with the increase in the number of nests. Based on territory size (the mean NND = 7.8 km), the study area can hold 13 nests. The process and mechanism of the dynamics of the number of nests were discussed, focusing on territoriality and weather effects.     

Factors affecting breeding habitat selection in a cliff-nesting peregrine Falco peregrinus population

We studied factors affecting breeding habitat selection in a population of cliff-nesting peregrines Falco peregrinus across multiple spatial levels (cliff site, cliff context and land-use of the surrounding landscape), over a 2,100 km² study area in the Alps (Italy and Switzerland). We detected 30 breeding pairs (density: 1.43 territorial pairs/100 km²), whose territories were uniformly distributed over the study area. We compared 15 habitat features characterising occupied cliffs and 30 randomly selected unoccupied cliffs by means of stepwise forward logistic regression and hierarchical partitioning. The logistic regression analysis showed that occupied cliffs were longer (horizontal length), steeper, and had a greater extension of urban areas in the surrounding landscape compared to non-occupied cliffs. The model had a discrimination ability of 0.95. Hierarchical partitioning indicated that the logistic regression model was appropriate. Neither the distance of cliffs to the nearest site occupied by a potential competitor and predator, the eagle owl Bubo bubo, which occurred at a low density (0.67 pairs/100 km²), nor the distance to the nearest site occupied by peregrines had any effect on the cliff suitability model. Therefore, habitat selection in cliff-nesting peregrines was mainly influenced by cliff site features and surrounding landscape characteristics, whereas the proximity to conspecifics and to an intraguild predator had no apparent effects on peregrine settlement in our study population.     

Modelling habitat use and distribution of golden eagles <Emphasis Type="Italic">Aquila chrysaetos</Emphasis> in a low-density area of the Iberian Peninsula

We analyse the current situation of the Golden eagle (Aquila chrysaetos) in the region of Galicia in NW Spain. At present, the entire Galician population (five pairs) is located within an area of about 2000 km² in the province of Ourense. To identify high-priority areas for golden eagle conservation, we derived predictive models of habitat suitability using logistic regression and a Geographic Information System (GIS). Specifically, to model the distribution of the breeding population we considered topographic features, land use and degree of humanization, using a 10 × 10 km grid. Presence/absence of golden eagle nests was used as the dependent variable; analyses were performed both considering current nesting areas and considering old nesting areas (1960s and 70s). At the spatial scale considered, the best predictors of habitat suitability for breeding were topographical variables indicative of rugged relief. For current nesting areas the most parsimonious model included maximum altitude. We consider that the predictive models obtained may be of use for the monitoring and conservation management of the golden eagle population in this region. Conservation problems associated with habitat constraints such as food supply, availability of nesting sites, changes in land use and human disturbance are discussed.     

Breeding success of the Eurasian eagle owl (<Emphasis Type="Italic">Bubo bubo</Emphasis>) and rodent population dynamics

The dependence of the breeding success of the eagle owl on the population dynamics of rodents, which are a staple of its diet in Mordovia, was traced. At peak numbers of rodents, large clutches and a high survival rate of fledglings were observed in the breeding pairs; after a year of depression of rodent populations, in the following year, the pairs do not nest at all or their breeding success is reduced to a minimum due to the death of the clutches. In 52% of the cases, the nesting pairs laid three eggs; in 31%, two eggs; in 9%, four eggs; in 4%, one egg or five eggs. The average clutch size was 2.78 ± 0.17. The average number of chicks grown from a successful nest was 2.41 ± 0.27. The nests in Mordovia were located at a distance of 1.1–3.7 km from residential areas.     

The breeding population of the Red-footed Falcon (Falco vespertinus) in the Sivash, Ukraine

The breeding numbers and habitat choice of Red-footed Falcons were studied in the Sivash, Ukraine in May 1992. About 40 % of the area and 32.5 km of hedgerows were counted. Red-footed Falcons were breeding dispersed and solitary or in small colonies of less than five pairs. Most pairs were breeding in hedgerows with on average 1–2 pairs per km. A total of 250 to 500 pairs is estimated to breed in the Sivash area.     

Using Corine Land Cover Habitat Database for the analysis of breeding bird habitat: case study of white storks (Ciconia ciconia) from northern Croatia

The purpose of this study was to find out whether a set of habitat characteristics, derived from the National Corine Land Cover (CLC) database of habitat types, could indicate the occurrence of white stork nests in a settlement. The analyses were performed for the settlements closer than 35 km from the Drava River (northern Croatia). Sixteen habitat characteristics were determined around 257 settlements occupied with white stork nests and 152 control sites without white stork nests within the same geographic region. We performed multivariate inspection of the data and a non-metric multidimensional preference analysis. The best variables for stork habitat selection were: distance to the nearest grassland habitat (P < 0.0001), distance to three nearest grassland habitats (P < 0.0001), altitude of the settlements above the sea level (P < 0.001), sum of distances to the three nearest agricultural mosaic habitats (P < 0.005) and standardized area proportion of forests (P < 0.05). The explanatory capacity of the model was 81.1%. We conclude that it is possible to define a small number of habitat characteristics derived from CLC database which can indicate the occurrence of white stork nests.     

Spacing of Golden Eagle Aquila chrysaetos nests in relation to nest site and food availability

A regular nest spacing of Golden Eagle pairs was found in every carefully searched area within the species range in Sweden. The spacing regularity of nests used by pairs in forests (mostly tree-nesting) was similar to that in mountain areas (cliff-nesting), indicating that regular nest spacing is affected more by spacing behaviour than by shortage of nest sites. Distances to nearest neighbours were shorter in the mountain region (mean distance 102 km) than in the forests (170) of northern Sweden. Densities of the most important prey species for Golden Eagle were apparently higher in the mountains than in the forests. Differences in topography and habitat diversity between the two regions may also have contributed to the difference in breeding density.     

High survival rate and site fidelity in the Siberian Tit Parus cinctus, a focal species of the taiga

The Siberian Tit Parus cinctus population of Finland, and probably of the whole of Fennoscandia, has declined dramatically during this century. Understanding its population dynamics is essential for its conservation. We studied annual survival rate and dispersal distance of both breeding and fledgling Siberian Tits during 1989-97 in a moderately managed forest habitat near the southern border of its range in Kuusamo, northeastern Finland. Breeding density was low, averaging 0.51 pairs/km in a nestbox area of about 42 km². This was probably an underestimate, because we did not search for nests in natural holes. However, following its population decline, overall densities at the southern border of the range are low. The study area was, however, suitable breeding habitat as reflected by their high nesting success. Brood size at fledging averaged 7.45 young, and reproductive output was 6.16 young per breeding pair, including failed nests. Clutch size adjustment was successful among pairs producing fledglings because, on average, 92.6% of the eggs laid produced young in successful broods. Median distance between consecutive breeding attempts was 100 m for both males and females (range 0–2500 m and 0–6000 m, respectively). Natal dispersal distance was significantly longer in females than in males. We applied Cormack-Jolly-Seber modelling to estimate survival and recapture probabilities separately. Survival of breeding birds was not sex-related, averaging 0.69 annually. Some of the ringed fledglings (3.0%) were later captured as breeders in the area. This is an underestimate of local survival rate due to incomplete recapturing of breeding birds. The implications of these results with respect to the conservation status of the species are discussed.     

扎龙自然保护区丹顶鹤(Grus japonensis)巢的内分布型及巢域

为了探讨丹顶鹤繁殖种群的空间分布,2002～2006年的4～5月份,在黑龙江扎龙国家级自然保护区,采用定点观察法、无样地取样法、GPS定位等研究方法和分布距离指数、最近邻体法等衡量指标对丹顶鹤(Grus japonensis)巢的内分布型及巢域进行了研究.结果表明:(1)扎龙保护区丹顶鹤巢的内分布型,I2002=2.140>2,I2003=2.048>2,I2004=2.093>2, I2006=3.263>2,均为聚集分布;(2)在假设扎龙保护区丹顶鹤巢域面积等于领域面积、巢域形状为圆形且所有个体面积大小相等的前提下,丹顶鹤的巢域为(0.510±0.019)km2,年度间有所差异,分别为2002年(0.542±0.257)km2、2003年(0.569±0.067)km2、2004年(0.557±0.054)km2、2006年(0.344±0.119)km2.分析表明,丹顶鹤对于栖息生境的整体分布和繁殖微生境质量的变化具有一定适应和应答的能力.为了更有效地验证本文的研究结果并对丹顶鹤进行保护,还有待于长期监测并进一步研究.     

Long‐term breeding demography and density dependence in an increasing population of Golden Eagles Aquila chrysaetos

Few studies have quantified the dynamics of recovering populations of large raptors using long‐term, spatially explicit studies. Using data collected over 37 years in the western Italian Alps, we assessed the trends in distribution, abundance, fecundity and breeding population structure of Golden Eagles Aquila chrysaetos. Using the spatial distribution of territory centroids in 2007, we found that the spatial distribution of eagle territories was over‐dispersed up to 3 km. Although population size and total productivity increased from 1972 to 2008, the proportion of pairs that laid eggs showed a strong decline, falling to no more than 50% after 2003. On average, 15% of successful nests produced two fledglings, and productivity also declined over time. No significant relationship between population growth rate and total population size was detected, but the percentage of pairs that bred and breeding success showed evidence of density dependence, as they declined significantly with increasing density. Our results suggest that density dependence, operating across heterogeneous habitats, is currently regulating this population, while the carrying capacity may still be increasing. This may explain the apparent paradox of reduced breeding effort despite increasing total productivity.     

Breeding density,habitat selection and reproductive rates of the Peregrine Falcon Falco peregrinus in Álava (northern Spain)

A population of 33–35 pairs of Peregrine Falcon in álava (north Spain) was studied with the aim of assessing the habitat attributes that influence breeding density, habitat selection and breeding success. A strong relationship was found between density of the species in each UTM (Universal Transverse Mercator) square of 10 × 10 km and cliff availability. Habitat selection was analysed by comparing 15 variables in 33 occupied and 25 unoccupied cliffs located at least 2 km from the nearest Peregrine pair. Significant differences were found in five variables: cliff dominance, distance to the nearest Golden Eagle Aquila chrysaetos nesting cliff, steepness and altitude (all showing larger values in occupied cliffs), and cliff orientation, with occupied cliffs facing preferably south and east. Orientation, dominance and distance to the nearest Golden Eagle pair, and the distance to the nearest Eagle Owl Bubo bubo nesting cliff, were included in a discriminant analysis which classified 82.76% of the cliffs correctly. The productivity of the studied population was 1.44 young/territorial pair (n = 45), and no consistent relationship was found between breeding success and habitat variables.     

Origin and genetic structure of white-tailed sea eagles (<Emphasis Type="Italic">Haliaeetus albicilla</Emphasis>) in the Czech Republic: an analysis of breeding distribution,ringing data and DNA microsatellites

The population of white-tailed sea eagles (Haliaeetus albicilla) in the Czech Republic declined dramatically during the twentieth century. None were observed in the area for more than 60 years until population recoveries were observed beginning in the 1980s. It is currently estimated that 25–30 breeding pairs of white-tailed sea eagles nest in the Czech Republic. This article analyses surveillance data from three periods between 1973 and 2003 on the occurrence and nesting of white-tailed sea eagles in the Czech Republic. We investigated recolonization of European white-tailed sea eagles in the Czech Republic in terms of migration patterns and population structures. Bird ringing data suggest the Czech population may be recovered from various areas encompassing northern Europe. Using data collected by DNA microsatellite, no population structure was revealed through Bayesian and cluster analyses with an existing Hardy–Weinberg equilibrium, which suggests mixed panmictic populations of white-tailed sea eagles in the Czech Republic and Slovakia. While analysis of genetic diversity showed no difference between recovered populations in the southeastern Czech Republic and those persisting in Slovakia, there was genetic diversity between eagles of the southeastern subpopulation and eagles in other parts of the Czech Republic. Taken together, these observations on the population structure of white-tailed sea eagles in the Czech Republic imply that other European birds contributed to the recovery of the Czech population, likely through breeding mixture with an identifiable centre in the southeastern Czech Republic.     

Translocation of threatened New Zealand falcons to vineyards increases nest attendance, brooding and feeding rates

Anthropogenic landscapes can be rich in resources, and may in some cases provide potential habitat for species whose natural habitat has declined. We used remote videography to assess whether reintroducing individuals of the threatened New Zealand falcon Falco novaeseelandiae into a highly modified agricultural habitat affected the feeding rates of breeding falcons or related breeding behavior such as nest attendance and brooding rates. Over 2,800 recording hours of footage were used to compare the behavior of falcons living in six natural nests (in unmanaged, hilly terrain between 4 km and 20 km from the nearest vineyard), with that of four breeding falcon pairs that had been transported into vineyards and nested within 500 m of the nearest vineyard. Falcons in vineyard nests had higher feeding rates, higher nest attendance, and higher brooding rates. As chick age increased, parents in vineyard nests fed chicks a greater amount of total prey and larger prey items on average than did parents in hill nests. Parents with larger broods brought in larger prey items and a greater total sum of prey biomass. Nevertheless, chicks in nests containing siblings received less daily biomass per individual than single chicks. Some of these results can be attributed to the supplementary feeding of falcons in vineyards. However, even after removing supplementary food from our analysis, falcons in vineyards still fed larger prey items to chicks than did parents in hill nests, suggesting that the anthropogenic habitat may be a viable source of quality food. Although agricultural regions globally are rarely associated with raptor conservation, these results suggest that translocating New Zealand falcons into vineyards has potential for the conservation of this species.     

Modelling the spatial distribution of White Stork Ciconia ciconia breeding populations in Southeast Europe

Capsule Spatial environmental modelling well predicted nesting distribution of the White stork in Southeast Europe and can be used in conservation planning with respect to climate change.

Aims To create spatial models for predicting White Stork presence and densities in the Southeast Europe to identify areas of suitable habitat for White Storks.

Methods We quantified the habitat used by nesting White storks in Southeast Europe. Using spatial modelling, we defined a set of free and available online environmental variables that predict the breeding localities of the species. We employed pseudo-absences and the kriging of the residuals in order to create predictive models of nest presence and density.

Results The presence–absence model was found to be precise in predicting the presence of nests. Both density and presence of breeding pairs were best explained negatively by elevation, slope, minimum temperature during May, and distance to the nearest human settlement and positively by topographic wetness index, total area of human settlement and spring precipitation.

Conclusion Our robust and easily repeatable models offer a conservation tool to reveal suitable but unoccupied localities for breeding White Storks pairs which may inform our understanding of how climate change might affect the species' distribution in the future. For example, protecting White Storks on the Dalmatian coast may become even more significant in the future, because the Dalmatian coast is predicted as the only suitable breeding area in Croatia later this century.     

生境破碎化对丹顶鹤巢位选择的影响

1985、1995年和1998年4－5月,采用查阅保护区历史资料及实地调查方法,对辽宁双台河口国家级自然保护区内丹顶鹤（Grus japonensis)的主要营巢地－东郭苇场和赵圈河苇场的生境破碎化及丹顶鹤在2片苇场中的营巢状况和繁殖种群数量变动情况作了系统的考察和研究,发现丹顶鹤的营巢生境破碎严重,已由成片的芦苇湿地变成91个斑块,其中最小营巢斑块面积为0．37km^2,最小巢间距为304m,比过去资料记载的最小巢区面积缩小了0．72km^2,但繁殖种群数量变动不大,多年来一直维持在30对左右,丹顶鹤为了适应变化了的环境,已采取了缩小巢区面积的生态适应对策。     

蓝冠噪鹛繁殖期生境选择特征分析

2013年至2015年每年4—7月,在江西婺源境内对蓝冠噪鹛繁殖小群进行调查。观察并测量其繁殖地斑块海拔,距山地、水源及干扰源的距离,计算斑块面积、周长及形状指数,并在每个繁殖斑块的4个方向5km以外选取同样植被类型的对照斑块,比较繁殖斑块与对照斑块在以上7个因子的差异。结果表明繁殖斑块海拔,距山地距离和距干扰距离显著小于对照斑块。说明在斑块尺度上,蓝冠噪鹛繁殖期倾向于选择低海拔阔叶林,且在离山地更近的村庄附近繁殖,这可能与食物丰富和天敌较少有关。在微生境尺度,选择繁殖点B在巢区及同一片阔叶林中无噪鹛筑巢的对照区进行10个生态因子的测量,并用资源选择函数以及Vanderploeg和Scavia选择系数进行分析。资源选择函数结果表明草本密度、草本高度在微生境尺度对蓝冠噪鹛生境选择贡献最大;而Vanderploeg和Scavia选择系数结果表明蓝冠噪鹛喜在胸径较粗(40—80cm)的朴树、枫杨和枫香3种树上筑巢,筑巢偏好树高20m以上及草本盖度较高(60%—90%)的生境。综合两种分析结果,在微生境尺度蓝冠噪鹛对筑巢树种及高度具有选择性,对巢区隐蔽性有所要求,巢下草本情况可以反映昆虫等食物资源状况,说明蓝冠噪鹛繁殖期偏好在食物相对丰富的区域筑巢。     

Density‐dependent effects on reproductive performance in a recovering population of White‐tailed Eagles Haliaeetus albicilla

Understanding the mechanisms that shape density‐dependent processes and population dynamics is often essential for species conservation. Two key mechanisms of density‐dependent reductions in reproductive performance are a limited access to foraging habitats (the habitat heterogeneity hypothesis) and territorial aggression towards conspecifics (the interference competition hypothesis) at high population densities. Disentangling the relative importance of these mechanisms within populations below their carrying capacity is important for the evaluation of the success of conservation measures. However, relatively few studies have attempted to quantify the relative importance of both mechanisms for the reproductive performance of a population. Many raptor populations are ideal model systems to investigate density‐dependent effects because they are currently recovering from human‐induced reductions during the last decades. Using a 14‐year dataset, we combined analyses of individual reproductive performance with a mechanistic population model to investigate early signs of density‐dependent regulation in a population of White‐tailed Eagles Haliaeetus albicilla in north‐east Germany. We found a negative effect of the number of neighbouring breeding pairs and a positive effect of water surface area (as a proxy for the availability of favourable foraging habitat) on breeding success and on the average number of nestlings. The mean nearest neighbour distance between breeding pairs has decreased, and the mean distance of nests to the nearest water body has increased over the last 14 years. Moreover, the population model indicates that even though the population is still growing, carrying capacity could be reached at about 500–950 territorial pairs. These results suggest that the selection of nesting sites is determined by a trade‐off between the distance to favourable foraging habitat and the distance to neighbouring breeding pairs. To avoid increasing competition with conspecifics, due to continued population growth, breeding pairs seem to select increasingly suboptimal habitats. Therefore, our results suggest that the habitat heterogeneity and interference competition hypotheses are not necessarily mutually exclusive as mechanisms of density‐dependent population regulation, but can determine the reproductive performance of a raptor population simultaneously. Thus, a future decline in breeding success does not necessarily reflect a decrease in habitat quality but may rather be a consequence of density‐dependent mechanisms. This information may be useful for the interpretation of population trends and for the development of appropriate management strategies for recovering raptor populations.     

Spatial distribution and breeding territories of Bonelli’s Eagle Aquila fasciata in the western Anti-Atlas Mountains,Morocco

The North African population of Bonelli’s Eagle Aquila fasciata (Vieillot, 1822) is limited to the south by the northern fringe of the Sahara Desert. This study provides the first data on the spatial distribution and density of breeding Bonelli’s Eagles in south-west Morocco, at the southern limit of their breeding distribution in the Western Palearctic. We used broad-scale sampling to investigate spatial patterns in occupancy of territorial pairs of Bonelli’s Eagles in an area of ～29 715 km2 in the western Anti-Atlas Mountains, southern Morocco, during 2016–2018. We found 28 nesting territories containing 40 used nests, heterogeneously distributed in areas of high topographic variation, from 60 to 1 890 m asl. The average nearest-neighbour nest distance was 14.12 ± 9.90 km and varied from 2.65 km in the north-west to 37.80 km in the pre-Saharan lands in the south-west portion of the study area. This work shows the importance of the western Anti-Atlas Mountains as one of the most significant strongholds of the species in Morocco. However, there is a need for systematic analyses of the different factors affecting the distribution of the species to implement conservation actions of this peripheral population.     

DISPERSION, BREEDING AND PREY OF THE HEN HARRIER CIRCUS CYANEUS IN GLEN DYE, KINCARDINESHIRE

Hen Harriers were studied on a grouse moor in northeastern Scotland from 1970-74. Numbers in spring were fairly stable, and the 24 nesting territories occupied in 1974 were regularly dispersed with a mean nearest neighbour distance of 1.52 ± s. e. 0.09 km. Many pairs apparently failed to breed and left the area. The mean clutch size of those remaining was 4.70 ± s. e. 0.24 (n= 27) and the mean number of young fledged per successful nest was 3.11 ± s. e. 0.26 (n= 19). Young males were more likely to disperse far from the study area than young females. The variety of prey species observed from hides at five nests was very limited, and comprised mainly pipits, grouse chicks and lagomorphs. Estimates by weight suggest that grouse and lagomorphs accounted for 89% of all prey. Males brought more small items and fewer large items to nests than females, and on average provided 72% of all prey items seen during watches from the hides. On the basis of studies of prey at three nests in 1974, and counts of grouse in spring and late summer, harrier predation was estimated to have reduced the number of grouse which might otherwise have survived to late July that year by a maximum of 7.4%.     

Predator presence may benefit: kestrels protect curlew nests against nest predators

We studied whether the presence of breeding kestrels (Falco tinnunculus) affected nest predation and breeding habitat selection of curlews (Numenius arquata) on an open flat farmland area in western Finland. We searched for nests of curlews from an area of 6 km² during 1985–1993. For each nest found, we recorded the fate of the nest, and the distance to the nearest kestrel nest and to the nearest perch. We measured the impact of breeding kestrels on nest predation by constructing artificial curlew nests in the vicinity of ten kestrel nests in 1993. Curlew nests were closer to kestrel nests than expected from random distribution, eventhough kestrels fed on average 5.5% of curlew chick production. Predation risk by kestrels was lower than predation risk by corvids and other generalist predators, which predated 9% of curlew nests surviving farming practices and an unknown proportion of chicks. Artificial nest experiment showed that nest predation was lower close to kestrel nests than further away suggesting that the breeding association of curlews and kestrels was a behavioural adaptation against nest predation. Thus, the presence of a predator may sometimes be beneficial to prey, and prey animals have behavioural adaptations to these situations.