Why don't all siblicidal eagles lay insurance eggs? The egg quality hypothesis

Several species of birds lay second eggs that are eliminatedby the siblicidal behavior of the first-hatched chick. A widelyaccepted explanation for the occurrence of these second eggsis insurance against complete nest failure. However, if insuranceis seen as an important breeding strategy for two-egg (c/2)layers, the question arises why single-egg species do not layinsurance eggs. The insurance-egg hypothesis predicts that extraeggs should occur where hatch failure is not trivial, whichmay be particularly prevalent in dense populations. Neitherprediction was supported for siblicidal l Wahlberg's eaglesAquila wahlberge Neither could food constraints or allometricrelationships explain the small one-egg clutch (c/1) of thisspecies Instead, clutch size was experimentally shown to berelated to optimal brood size: parents given two young wereunable to rear them, and subsequent breeding opportunities weresignificantly curtailed. Since clutch and brood size are similarlyrelated in c/2 eagles, insurance may be an exaptation of thesecond egg. One-egg spedes, however, appear to trade second(insurance) eggs for large, high-quality eggs, which enhancehatchability and chick viability. This was borne out by comparisonof the world's c/1 eagles, which lay significantly (p<.01)larger eggs than c/2 eagles of the same body size. Large Wahlberg'seagle eggs also showed significantly (p=.02) greater hatchabilitythan small eggs, and other studies show enhanced survival/qualityfor chicks from large eggs. Because only longer-lived eaglestraded two eggs for single, large eggs, this is consistent withthe idea of selection for offspring quality in long-lived species.I condude that higher hatchability of single, large eggs decreasesthe need for an insurance egg and simultaneously enhances viabilityof resultant chicks in sibliddal eagles and possibly sulids.     

Identifying key habitats for the conservation of Bonelli's Eagle Aquila fasciata using radiotracking

Identifying the priority habitats of endangered species is crucial to implementing effective conservation actions. We characterize the key habitats used by Bonelli's Eagle Aquila fasciata, an umbrella and flagship species that is endangered in Mediterranean countries. We radiotracked 17 breeding individuals (10 males and seven females) in Catalonia (NE Iberian Peninsula) and used compositional analysis to determine the key habitats in home‐ranges of both sexes. The main habitats identified within the home‐range area were scrubland, coniferous forests, cropland, sclerophyllous forests, rock outcrops and urban areas, with little difference in habitat use between the sexes. Bonelli's Eagles preferred rocky habitats as breeding areas and scrubland as foraging areas, as these hold the highest abundance of their main prey, Rabbits Oryctolagus cuniculus and Red‐legged Partridges Alectoris rufa. Habitat selection varied seasonally in foraging areas: scrubland was the most preferred habitat type during the breeding season, whereas rocky areas were preferred during the non‐breeding season (although scrubland was also highly selected). Urban areas were avoided both as breeding and as foraging areas. Home‐range size was inversely correlated with the proportion of scrubland, suggesting that this is a key habitat for Bonelli's Eagle. To conserve this species effectively, policies that ensure the preservation of the cliffs used as breeding sites, as well as suitable management of the scrubland used for foraging, should be implemented in the areas inhabited by this species. The promotion of traditional land uses and management techniques that will enhance open areas in Mediterranean landscapes should in the future play an essential role in the conservation of Bonelli's Eagle in Mediterranean habitats.     

Eighteen polymorphic microsatellite markers for the highly endangered Spanish imperial eagle (Aquila adalberti) and related species

Here we describe the development of 18 polymorphic microsatellite markers for the endangered Spanish imperial eagle (Aquila adalberti). Microsatellites were tested in five other raptor species. These markers were revealed as good molecular tools for genetic population studies, individual identification and parentage assessment in Spanish imperial eagle and closely related species.     

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.     

How far away in an hour? Daily movements of juvenile golden eagles ( Aquila chrysaetos ) tracked with satellite telemetry

We tracked the daily movements of three juvenile golden eagles (Aquila chrysaetos) using satellite telemetry. Straight distances covered in an hour and throughout a day were calculated. Daily movements of golden eagles are mostly characterized by short-distance excursions, with 64% of the distances covered in an hour shorter than 1 km and 95% shorter than 9 km. Both the longest movements and the largest proportion of long-distance movements, were concentrated between 1100 and 1800 hours, the peak of daily activities. Average hourly distances during that peak oscillated between 2 and 6 km, with records of more than 20 km. Distances covered in a day ranged between 0.1 and 53.2 km with an average of 14.0 km (SD=13.4). Differences in the distances covered at different times of the day probably reflect a balance between the temporal pattern of preferred prey’s activity and the eagles’ progressive satiation along the day on one hand, and the higher likelihood of thermal and updraughts (which facilitate long-distance movements) occurring at noon and the early afternoon, on the other.     

Verreaux's eagles (Aquila verreauxi) as potential predators of hamadryas baboons (Papio hamadryas hamadryas) in Eritrea

In this paper we describe for the first time encounters of Verreaux's eagle (Aquila verreauxi) with hamadryas baboons (Papio hamadryas hamadryas) in the central highlands of Eritrea (15° 22′ N, 38° 58′ E, 2300 m). During 12 h of observation on 4 days, we observed four encounters of Verreaux's eagles with baboons, of which three can be classified as possible attacks. The baboons always responded with alarm calls. In three cases some immatures rushed to adult group members and clung to them, particularly to the adult male. Adult males threatened the eagle, and the whole group did not flee. The response of baboons towards smaller raptors like tawny eagles (Aquila rapax) and black kites (Milvus migrans) was very different. The adult baboons gave no alarm barks but scanned the raptors. The permanent presence of a pair of Verreaux's eagles in the home range of the baboons may represent a considerable predation pressure, at least for immature baboons. Am. J. Primatol. 47:61–66, 1999. © 1999 Wiley‐Liss, Inc.