Simultaneous Effect Of Habitat And Age On Reproductive Success Of Imperial Eagles (Aquila Heliaca) In Hungary

Abstract

An unexpected expansion of the Eastern Imperial Eagle (Aquila heliaca) population was observed in East Hungary from mountainous habitat into lowlands from 1989 onwards. Here the population markedly increased from 2 to 59 breeding pairs by 2006, while the mountainous population remained more or less stable with 12-17 breeding pairs. At the beginning of the expansion process the nearest neighbour distances between breeding pairs was lower in the mountains than in the lowlands, but presently they are similar, indicating a saturation process in the lowland areas, but no density dependence was revealed on breeding success. During the study period a higher ratio of non-adult pairs was observed in the lowland territories (49%) than in the mountains (22%). We found that both age and habitat influenced breeding success. We also found that age-effect was significant on success rate (i.e. the ratio of pairs that produce at least one chick), while habitat-effect was more evident on fledging success (i.e. the number of fledglings per productive pair). The overall productivity (i.e. number of fledglings per breeding pair) was affected primarily by the age of the pairs, but the interaction term of age x habitat also was significant. We suppose that better feeding possibilities (closer foraging areas and larger prey density) could explain the higher fledging success in the lowlands. We also predicted that pairs inhabiting agricultural areas in the lowlands will have a reduced success rate due to higher human disturbance, together with an age effect of the breeding pairs. Therefore adult pairs probably can habituate to disturbance even if it happens in the close vicinity of their nesting sites.

Natural expansion versus translocation in a previously human‐persecuted bird of prey

“…For these reasons, young individuals are less likely to find and fill vacancies in the natal area than older individuals, and breeding dispersal outside the population limits gives more chance of finding a potential territory. In fact, as our results show, during the process of population expansion, the number of immature pairs increases in territories with higher NND values (Ferrer et al., , , ; González et al., ; Horváth et al., ; Margalida et al., ), suggesting that immature pairs tend to establish territories far from existing nests. Where immature individuals are able to occupy high‐quality territories, values of productivity do not differ from adults in high‐quality territories, so productivity is not correlated only with the age of breeding pairs (Ferrer & Bisson, ; Ferrer et al., ; Horváth et al., ).…”

“…Expanding population processes show again that quality of territory has a major influence on the productivity of breeding pairs (Ferrer & Bisson, ; Ferrer & Donazar, ; Ferrer et al., ). The presence of empty habitat adjacent to existing population perimeters allows immature pairs to settle near their natal population (Horváth et al., ; Kivela et al., ), but reintroduction projects allow the occupation of vacant high‐quality habitat not limited by the existing population's distribution.…”

“…To allow for annual variation in reproductive performance, we adjusted productivity (number of fledglings) for year effects by subtracting annual means from the raw data. Corrected data are referred to as relative values (Ferrer & Bisson, ; Horváth et al., ; Penteriani, Balbontin, & Ferrer, ). Also, as in other studies of raptors, territory quality was estimated by frequency of occupancy (Ferrer & Donazar, ; Newton, ; Sergio & Newton, ).…”

Reintroducing endangered raptors: A case study of supplementary feeding and removal of nestlings from wild populations

“…For the calculation of productivity values for territories, we controlled for a potential year effect by subtracting mean annual productivities from the original data on breeding success (relative productivity, Ferrer & Bisson, ; Horváth et al., ; Penteriani, Balbontin, & Ferrer, ). Hatching date was given a numerical value by considering the earliest hatching date of each year as day 1.…”

Towards understanding and resolving the conflict related to the Eastern Imperial Eagle ( Aquila heliaca ) conservation with participatory management planning

“…In the early 1980s, the population reached its lowest, with approximately 20 breeding pairs, but since then has continually increased, mostly due to concentrated monitoring and conservation efforts Horváth et al, 2009). The breeding area has expanded towards lowland agricultural areas, while habitats in mountainous areas have decreased (Horváth et al, 2014). The Eastern Imperial Eagle nests in patches of old forest or uses solitary trees or groups of trees for nesting, and research indicates that it is highly sensitive to disturbance (Kovács et al, 2005).…”