Cliff-nesting Raptors Research Articles

Drivers of scarcity in the globally threatened Taita Falcon Falco fasciinucha: competition and habitat quality in the eastern escarpment region of South Africa

Summary The Taita Falcon Falco fasciinucha is known to occur and breed at only a few locations in eastern and southern Africa and is currently listed as globally “Vulnerable” and “Critically Endangered” in South Africa. An accurate estimation of its conservation status is however hampered by a lack of data and understanding of the species’ habitat requirements and competitive interactions with congeners. Our aim was to address some of these knowledge gaps. We conducted cliff-nesting raptor surveys across a substantial area of the Mpumalanga/Limpopo escarpment in north-eastern South Africa and modelled habitat suitability for nesting Taita Falcons in relation to the proximity of conspecifics and a community of five other sympatric cliff-nesting raptor species, and in relation to a suite of biotic and abiotic environmental variables. Results suggested the location of Taita Falcon nest sites was negatively associated with distance to the nearest pair of conspecifics and the nearest pair of Lanner Falcons Falco biarmicus, and positively associated with tracts of intact, unfragmented forest and woodland around the base of the cliffs. Our results indicated that Taita Falcon and Lanner Falcon appeared to be responding in opposite ways to a directional change in environmental conditions. This response appeared to be detrimental to Taita Falcon and beneficial to Lanner Falcon. Furthermore, the degradation and destruction of Afrotropical woodland and forest is a documented and ongoing reality, both locally and across much of the Taita Falcon’s global distribution. We argue that our findings are sufficient to justify uplisting Taita Falcon to globally “Endangered”.

Direct and Indirect Effects of Nesting Site Characteristics for a Cliff-Nesting Raptor in Western Alaska

Habitat suitability for breeding birds is defined at scales ranging from the landscape to individual nesting sites. Nesting site characteristics that govern exposure to inclement weather may affect breeding success, although attempts to understand this effect for Arctic breeding raptors have yielded ambiguous results. Further, breeding adults incur substantial costs from incubating eggs and brooding nestlings, and it is possible that greater site exposure results in increased nest attendance rates, increasing their cost of breeding. We quantified nesting site characteristics of Gyrfalcons (Falco rusticolus) and assessed how breeding parameters and nest attendance rates varied by protective site qualities on Alaska's Seward Peninsula, 2014–2019. The degree of physical exposure in the horizontal plane correlated negatively with the probability of hatching and fledging (provided hatch occurred), as well as overall productivity. The negative effect of horizontal exposure on the probability of fledging and productivity was greatest at nesting sites that were also more exposed in the vertical plane, although this interaction did not affect the probability of hatching. Early breeding pairs had higher productivity and tended to select more protected nesting sites. Additionally, nest attendance rates were higher in more horizontally exposed nesting sites, particularly when nestlings were approximately 2 wk old. The increased nest attendance and concurrent decreased productivity associated with greater nesting site exposure demonstrated that nesting site characteristics can have direct and indirect effects on Arctic breeding raptors and also highlight the importance of small-scale variables when evaluating habitat suitability.

Direct and Indirect Effects of Nesting Site Characteristics for a Cliff-Nesting Raptor in Western Alaska

Habitat suitability for breeding birds is defined at scales ranging from the landscape to individual nesting sites. Nesting site characteristics that govern exposure to inclement weather may affect breeding success, although attempts to understand this effect for Arctic breeding raptors have yielded ambiguous results. Further, breeding adults incur substantial costs from incubating eggs and brooding nestlings, and it is possible that greater site exposure results in increased nest attendance rates, increasing their cost of breeding. We quantified nesting site characteristics of Gyrfalcons (Falco rusticolus) and assessed how breeding parameters and nest attendance rates varied by protective site qualities on Alaska's Seward Peninsula, 2014–2019. The degree of physical exposure in the horizontal plane correlated negatively with the probability of hatching and fledging (provided hatch occurred), as well as overall productivity. The negative effect of horizontal exposure on the probability of fledging and productivity was greatest at nesting sites that were also more exposed in the vertical plane, although this interaction did not affect the probability of hatching. Early breeding pairs had higher productivity and tended to select more protected nesting sites. Additionally, nest attendance rates were higher in more horizontally exposed nesting sites, particularly when nestlings were approximately 2 wk old. The increased nest attendance and concurrent decreased productivity associated with greater nesting site exposure demonstrated that nesting site characteristics can have direct and indirect effects on Arctic breeding raptors and also highlight the importance of small-scale variables when evaluating habitat suitability.

Using Motion-Activated Trail Cameras to Study Diet and Productivity of Cliff-Nesting Golden Eagles

Studies of cliff-nesting raptors can be challenging because direct observations of nest contents are difficult. Our goals were to develop a protocol for installing motion-activated trail cameras at Golden Eagle (Aquila chrysaetos) nests to record diet information and productivity, and to estimate prey detection probability using different diet study methods. In 2014 and 2015, we installed cameras at 12 Golden Eagle nests with 18–42-d-old nestlings. Following installation, we monitored adult behavior using direct observation and post-installation image review. At two nests, adult eagles did not return to nests or exhibited behaviors suggesting avoidance of the cameras, but returned to the nests after cameras were removed. We visited the 10 remaining nests every 4 d to collect prey remains and pellets to generate prey-specific detection estimates for both images, and prey remains and pellets. Compared to inspection of prey remains and pellets, cameras recorded twice the number of prey (622 vs. 316), were more likely to detect the smallest and largest prey, and cost half as much. Cameras recorded productivity, fledging dates, and in one case, a nestling death. Trail cameras may be a reliable and cost-effective option to address clearly defined research goals and obtain required information about eagle behavior and nest contents. However, cameras should be used judiciously because installation creates a persistent manipulation at the nest. Camera appearance should be minimized, and post-installation monitoring that allows for timely responses to nest-avoidance behavior by adult eagles is important to prevent adverse effects on nesting success.

Satellite factors influencing the impact of recreational activities on wildlife

Satellite factors influencing the impact of recreational activities on wildlife

Vulnerability to geomorphological hazards of an Arctic cliff-nesting raptor, the rough-legged hawk

Increase in temperature and precipitation associated with climate change may enhance the risk of destruction by geomorphological processes of nests or dens used by Arctic wildlife. We assessed nest vulnerability to mass movements and identified environmental factors associated with the persistence of nesting structures of rough-legged hawks (Buteo lagopus), a species that typically nests on steep slopes or cliffs. The study was conducted on Bylot Island (Nunavut) where 82 permanent hawk nesting structures, built mainly on sedimentary rocks, were monitored from 2007 to 2015. More than a quarter of known nests were destroyed during the course of the study and among those still intact, more than half were associated with a moderate to high risk of being destroyed. Nest survival analysis suggested a relatively short persistence of rough-legged hawk nesting structures on Bylot Island compared to other Arctic cliff-nesting species. Nest destruction probability increased for nests built on unconsolidated sediments, with heavy rainfall and temperature during the summer. The anticipated increase in precipitation and temperature due to climate change is likely to augment the exposure of hawk nests to mass movements, which could ultimately reduce the availability of suitable sites for the reproduction of this Arctic-nesting raptor.

Factors affecting the spatial distribution and breeding habitat of an insular cliff-nesting raptor community.

The specific spatial distribution and habitat association—strongly influenced by environmental factors or competitive interactions—are major issues in ecology and conservation. We located and georeferenced nesting sites of five cliff-nesting raptors (Egyptian vulture Neophron percnopterus [a locally extinct species], common buzzard Buteo buteo, osprey Pandion haliaetus, common kestrel Falco tinnunculus, Barbary falcon Falco peregrinus pelegrinoides), and common raven Corvus corax on one of the most biodiverse hotspot within the Canary Islands (Teno, Tenerife). We used generalized linear models to evaluate the factors affecting abundance, richness, and intra- and interspecific interactions. Raptor abundance increased with slope, shrub-covered area, and habitat diversity, and decreased with altitude, and forested and grassed areas. Richness increased with slope and decreased with altitude. Threatened species (osprey, Barbary falcon, and raven) occupied cliffs farther away from houses and roads, and more rugged areas than the non-threatened species. The models suggested that the probability of cliff occupation by buzzards, falcons, and ravens depended only on inter-specific interactions. Buzzard occupation increased with the distance to the nearest raven and kestrel nests, whereas falcons and ravens seek proximity to each other. Teno holds between 75% and 100% of the insular breeding populations of the most endangered species (osprey and raven), indicating the high conservation value of this area. Our study suggests that the preservation of rugged terrains and areas of low human pressure are key factors for raptor conservation and provide basic knowledge on the community structure and habitat associations to develop appropriated management actions for these fragile island populations.

Changes in Diurnal Cliff-Nesting Raptor Occurrence on the Ungalik River in Western Alaska: 1977, 1979, and 2008

Diurnal cliff-nesting raptors were inventoried on the Ungalik River, Alaska, in 1977 and 1979. In 2008 we resurveyed the drainage, replicating the techniques used in 1979. The density of nesting raptors during the late nesting season has doubled in the past three decades, from six occupied territories detected in 1977 and four in 1979 to 12 in 2008. A single Peregrine Falcon (Falco peregrinus) was sighted during aerial surveys in 1977, and a pair of Peregrine Falcons was detected during a boat survey in 1979; however, nesting by these birds was not confirmed. In contrast, we detected five occupied Peregrine Falcon territories along the Ungalik River in 2008. Other changes in cliff-nesting raptor occurrence included a decrease in occupied Gyrfalcon (Falco rusticolus) territories from four in 1977 to one in 1979 and two in 2008, a decrease in Rough-legged Hawk (Buteo lagopus) nests from one in 1979 (none in 1977) to none in 2008, and increases in Golden Eagle (Aquila chrysaetos) nests, from two in 1977 and 1979 to five in 2008. Changes in the number of nests of cliff-nesting raptors in this small population may have resulted, in part, from natural variation associated with changes in weather or prey abundance. However, it is likely that the increase in nesting Peregrine Falcons is related to global population recovery. Our data indicate that factors other than available nesting sites limit cliff-nesting raptor numbers along the Ungalik River. Spatial analysis indicated that cliff-nesting raptor nests were most often on hills or cliffs that face away from the coast, which is the source of most storms.

Ranging Behaviour of Eleonora's FalconsFalco eleonoraeDuring Chickrearing

The Eleonora's Falcon is a cliff-nesting raptor that breeds on isolated small islands adjusting its breeding season to coincide with the post-breeding autumn migration of its small passerine prey migrating over the sea, between late August and early October. Two adult female Eleonora's Falcons were equipped with Argos satellite transmitters during the chick-rearing period in Morocco giving the opportunity to study the ranging behaviour of the species during at least a part of the breeding season. Results showed that the falcons spent most of the time at sea during mornings, stayed mainly inland during afternoons, and rested in the colony during nights. Interestingly, although most distances were recorded shorter than 50 km away from the colony, movements took also place to areas located more than 100 km away. Locating and protecting these inland areas used for resting and foraging may be of interest for the conservation of the species in order to avoid perturbations such as poisoning and habitat destruction.

Use of digital trail cameras to study Bonelli's eagle diet during the nestling period

The study of avian diet is one of the most commonly discussed topics in Ornithology. Different methods such as direct observations of hunting, analysis of pellets and collection of prey remains have usually been employed to study avian diet. Fortunately, digital technologies have rapidly advanced in recent years, allowing researchers to increase our understanding of avian behaviour. Here we report the outcomes of a pilot project to study the diet of Bonelli's eagle (Aquila fasciata, Syn = Hieraaetus fasciatus) during the nestling period using digital trail cameras. We describe the monitoring system, provide results on dietary composition and discuss advantages and shortcomings of the method employed. Our results show that the main prey delivered to nests were pigeons (Columba spp.) and common rabbits (Oryctolagus cuniculus). One advantage of the method is the relative low cost of the material employed in contrast to digital video cameras. Disadvantages were the limited duration of power supply of the units and, because recordings can only be obtained at the end of the breeding season, it is not possible to fix the device if a problem arises. Nevertheless, in the light of our results, we recommend the use of digital trail cameras as an efficient, non-intrusive method to study the diet of cliff-nesting raptors, given that, in combination with traditional methods, it facilitates estimation of dietary composition in an objective, economic, contrastable and unbiased manner.

Detection Probability of Cliff-Nesting Raptors During Helicopter and Fixed-Wing Aircraft Surveys in Western Alaska

Abstract We conducted repeated aerial surveys for breeding cliff-nesting raptors on the Yukon Delta National Wildlife Refuge (YDNWR) in western Alaska to estimate detection probabilities of Gyrfalcons (Falco rusticolus), Golden Eagles (Aquila chrysaetos), Rough-legged Hawks (Buteo lagopus), and also Common Ravens (Corvus corax). Using the program PRESENCE, we modeled detection histories of each species based on single species occupancy modeling. We used different observers during four helicopter replicate surveys in the Kilbuck Mountains and five fixed-wing replicate surveys in the Ingakslugwat Hills near Bethel, AK. During helicopter surveys, Gyrfalcons had the highest detection probability estimate (; = 0.79; SE 0.05), followed by Golden Eagles ( = 0.68; SE 0.05), Common Ravens ( = 0.45; SE 0.17), and Rough-legged Hawks ( = 0.10; SE 0.11). Detection probabilities from fixed-wing aircraft in the Ingakslugwat Hills were similar to those from the helicopter in the Kilbuck Mountains for Gyrfalcons a...

Possible functions of alternative nests in raptors: the case of Bonelli’s Eagle

Four non-exclusive hypotheses have been proposed to explain the alternative nest-building behaviour of raptors: (1) nests as an advertising signal in territories, (2) frustration nests, (3) competition avoidance by nest-site and (4) reduction of nest ectoparasites. We report here data collected during an observational study of a population of Bonelli’s Eagle Hieraaetus fasciatus in southeastern Spain. Our data does not support the first two hypotheses based on the closeness of nests within territories, the lack of correlation between the number of nests and the distance to neighbours and the construction of secondary nests at similar frequencies after breeding failures as after successes. In contrast, the construction of alternative nests to avoid competition with other cliff-nesting raptor species breeding nearby was clearly important since 30% of the pairs obtained some direct benefit from the existence of alternative nests within their territories. We also found abundant Coleoptera (Dermestidae) and Diptera (Carnidae, Calliphoridae and Phoridae) as ectoparasites in nests, and the alternative use of nests, synergetically with the presence of greenery as mechanisms for avoiding ectoparasites, was an important factor for the breeding success of the eagle. Our data suggest that competition avoidance and, in particular, the reduction of nest ectoparasite hypotheses are the more plausible explanations for the maintenance of alternative nests in raptors.

A solar-powered transmitting video camera for monitoring cliff-nesting raptors

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Conservation status and community structure of cliff-nesting raptors and ravens on the Cape Peninsula, South Africa

We detail the sizes, spatial distributions and trends in nest site selection of cliff-nesting raptor and raven populations resident in the mountains of the Cape Peninsula, South Africa. We also assess the conservation value of these populations to inform the future management of the newly-established Table Mountain National Park (TMNP), and examine the structure and interrelations within the raptor community. The combined number, dispersion and density of nests (n = 96 nests, mean inter-nest distance = 0.59km, density = 30.0 pairs/100km2) are comparable with those of high-density raptor populations studied elsewhere in Africa and the world. Densities of Verreauxs' Eagle Aquila verreauxii (n = 2, 12.01km, 0.6 pairs/100km2, respectively) and Jackal Buzzard Buteo rufofuscus (n = 9, 4.63, 2.8 pairs/100km2), are low, Rock Kestrel Falco rupicolus (n = 44, 1.75km, 13.8 pairs/100km2) high and Peregrine Falcon Falco peregrinus (n = 19, 3.13km, 5.9 pairs/100km2) exceptional, relative to populations of the same or similar species in other areas. There are no comparable data for White-necked Raven Corvus albicollis (n = 22, 3.22km, 6.9 pairs/100km2). All species combined, and Peregrines in particular, significantly prefer high cliffs from the available habitat. Peregrines generally dominate the other species, may affect cliff site selection and dispersion in the rest of the community, and tend to locate their nests close to those of White-necked Ravens. Numbers of Verreauxs' Eagle are lower than recent historical levels, perhaps because key prey populations are depleted. Any future recovery of this large predator could subtly affect the entire assemblage. This cliff-nesting raptor community is a significant asset of the TMNP, and should be considered in management decisions taken in the Park, particularly those concerning the regulation of leisure activities in the vicinity of nesting areas.

Social and Sexual Monogamy in Translocated New Zealand Robin Populations Detected Using Minisatellite DNA

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Griffon VulturesGyps fulvusoccupying eyries of other cliff-nesting raptors

Griffon Vultures<i>Gyps fulvus</i>occupying eyries of other cliff-nesting raptors