Felipe Siverio

Causes of Raptor Admissions to a Wildlife Rehabilitation Center in Tenerife (Canary Islands)

Abstract We studied the causes of raptor admissions to the only wildlife rehabilitation center on the largest island of the Canarian Archipelago (Tenerife) over ten years (1998–2007). A total of 2611 birds of prey, belonging to nine falconiform diurnal raptor and four strigiform species, were admitted. The Eurasian Kestrel (Falco tinnunculus) and the Long-eared Owl (Asio otus) were the species most commonly admitted and jointly made up 85.6% of admissions. The most frequent causes of admission to the wildlife rehabilitation center were collisions (with cars, high-voltage electric transmission towers, etc.; 42.2%), starvation (5.1%) and entanglement in glue traps intended for rodents (4.7%). Poisoning and shooting were recorded for 2.4 and 1.5% of the birds admitted, respectively. Only collisions increased during the study period. A total of 1010 birds (44.4% of the total) were released to the wild following rehabilitation. We recommend more financial support for rehabilitation centers to develop detailed analytical diagnoses and rehabilitation services.

Density, habitat selection and breeding success of an insular population of Barbary Falcon Falco peregrinus pelegrinoides

We studied density, habitat selection and reproduction of Barbary Falcons Falco peregrinus pelegrinoides on Tenerife Island during 2004 and 2005. A total of 26 breeding pairs were counted, all of them occupying natural cliffs around the island. Density observed was 1.27 pairs/100 km2, and was positively correlated with cliff availability. Mean distance between neighbouring pairs was 5869 ± 3338 m, ranging from 1388–13 610 m; in some areas this value was as low as 2062 ± 673 m. Tenerife still shows potential for further increase regarding the observations of single females and the availability of potentially suitable but unoccupied cliffs. Falcons selected taller cliffs, more apart from roads and houses, near the coast, with lower presence of cultivated and urban areas, and associated with other cliff-nesting species. Stepwise discriminant analysis of habitat selection selected cliff height, nearest neighbour distance and distance to road, and correctly classified 71.1% of the cases. Productivity averaged 1.55 fledged young/pair and breeding success was 81.1%. No correlations were observed between habitat features and productivity. Since most territories are located in protected zones and human disturbance seems to be absent, special management measures are not necessary. However, further study into the biology of this population is required for effective and timely conservation of this species if need be.

Density, habitat selection and breeding biology of Common Buzzards Buteo buteo in an insular environment

Capsule Taller and sheltered cliffs located in rugged areas are selected for breeding and only some life history traits fit the predictions of the so‐called ‘insular’ syndrome. Aims To analyse the density and nesting habitat preferences of Buzzards on the island of Tenerife, and describe the life history traits of this population. Methods Density was studied by intensive field searching for all established pairs in a well‐defined area. Habitat features of breeding territories were compared with randomly selected sites using univariate and multivariate analysis (glm). Breeding biology was described based upon a total of 57 breeding attempts. Results Density was positively correlated with estimated surface of forested areas. The best model explaining characteristics of territory used for nesting reflected land ruggedness, nest shelter and distance to the nearest Barbary Falcon breeding site. Mean clutch size was 2.60 ± 0.82, productivity was 1.68 ± 0.97 and the percentage of successful pairs was 84.2%. Conclusions Buzzards mainly use cliffs to nest, especially taller and sheltered ones, located in rugged areas and in sympatry with Barbary Falcons. Characteristics of breeding territory did not predict productivity. All reproductive rates were similar to those reported for some continental populations except nesting success, which was higher.

Inter-insular variation of the diet of osprey Pandion haliaetus in the Canarian archipelago

Abstract 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.

Long-term monitoring of an insular population of Barbary Falcon Falco peregrinus pelegrinoides

Territory spacing and breeding rates of an insular population (north-western Tenerife, Canary Islands) of Barbary Falcon Falco peregrinus pelegrinoides was studied from 1993 to 2008. The population increased constantly since the outset, from two pairs in 1993 to 12 in 2008. Mean density was 5.48 pairs per 100 km2 and mean nearest neighbour distance was 3 119 m. The regularity of the spatial distribution pattern of the nests, observed in most years, may be maintained in the future despite the expectation that new pairs may occupy still-vacant territories. Considering the 79 breeding attempts analysed, the mean number of fledged young per territorial pair was 1.92, per laying pair was 2.0 (n = 76), and per successful pair was 2.24 (n = 68). No significant variations were observed between the annual mean number of fledged young per laying pair, nor between the number of fledged young of pairs according to density in a 5 km radius. All fledglings (brood size one to four) left the nest in the month of May. In order to avoid affecting breeding success, sporting activities practised in the breeding areas must be correctly managed by the appropriate authorities.

An Overlooked Cost for the Velvety Plumage of Owls: Entanglement in Adhesive Vegetation

Abstract We used data collected during 1995– 2007 at the only Wildlife Rehabilitation Center on Tenerife Island (Canary Islands) to quantify entanglement mortality of owls. At least 66 of 1,206 Long-eared (Asio otus) and 5 of 231 Barn (Tyto alba) owls admitted to the Wildlife Rehabilitation Center were entangled in burr bristlegrass (Setaria adhaerens). Twelve (18.2%) of the 66 Long-eared Owls died as a result of entanglement while one of five Barn Owls died. A higher incidence of entanglement occurred during summer, coinciding with seed-head ripening and dispersing recently-fledged owls. Velvety plumage may be an important cost for owls, and responsible for owls acting as seed dispersers.

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

Abstract 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.

Nectar and pollen of the invasive century plant Agave americana as a food resource for endemic birds

Capsule Flowers of an invasive plant species are more visited by native birds than flowers of ornithophilous endemic plants. Aims To describe the bird guild and its behaviour visiting the century plant Agave americana in an insular environment and to determine which factors are affecting visitation rates. Methods We noted number and species of birds visiting inflorescences on Tenerife, Canary Islands. We used multimodel inference of generalized linear models to analyse the factors affecting the number of visits and the visitor species richness. Results Eighty-one per cent of inflorescences were visited by eight native bird species. All species fed on nectar and only the Atlantic Canary fed also on pollen. Foraging behaviour varied among species. Visitation rate increased with density and diversity of birds and flower characteristics and decreased through the day. The number of species visiting the inflorescences increased with diversity and density of birds in the surroundings and decreased through the day. Conclusion The native bird community uses the invasive century plant as a feeding resource at a higher rate than it uses endemic ornithophilous plants. This could have negative effects for the pollination of endemic plants, but positive effects for birds.

Osprey (Pandion haliaetus) Use of Rhizoliths in Nest Building

The type of material used by Ospreys (Pandion haliaetus) for nest building or repair appears to depend on availability in the surrounding area. Natural material (bush or tree branches, grasses, algae, etc.) is today complemented by an endless range of human refuse (plastic bags, pieces of fishing net, cloth, string, etc.), which can occasionally prove hazardous both for broods (Poole 1989, Thibault et al. 2001, R. Triay pers. comm.) and for adult birds (Palma 2001). The disproportionate size of many nests (Cramp and Simmons 1980) may be a response to bad weather (e.g., high winds), as large nests tend to be more stable (Poole 1989). We here describe the manner in which some pairs of Osprey on the island of Boavista, Cape Verde, use unconventional nesting materials not previously reported. The island of Boavista (16u059N, 23u509W; 620 km2), situated 570 km from the coast of Senegal (west Africa), is the easternmost and one of the most arid of the islands that make up the Cape Verde archipelago. Topography consists primarily of stony tablelands and dune systems, with a few somewhat rugged regions (eroded mountains and low coastal cliffs). Although the Osprey population of Boavista was estimated at 5–8 pairs in the 1960s (Naurois 1987), 8 pairs (11 nests detected) in 1999 (Ontiveros 2003) and 11 pairs (25 nests detected) in 1998–2001 (Palma et al. 2004), our most recent and more systematic surveys (2005– 2007) revealed numbers of nests (both active and inactive) and pairs that exceeded previous estimates (78 nests and about 15 pairs; P. López unpubl. data). While visiting the south coast of Boavista in November 2001, we discovered an old nest on the smooth surface of a rocky point, ca. 2–3 m above sea level. A good part of the material still remaining consisted of rhizoliths (Fig. 1a), the original dimensions of which, perhaps measuring .0.5 m, had been reduced by erosion. These concretions, which may be attributed to Tamarix (Tamaricaceae; Nørrevang and Hartog 1984, W. Lobin pers. comm.), are frequently found in the dune systems of the island, where they occasionally outcrop vertically and can be mistaken for dry branches or sticks (Fig. 2). Subsequent surveys on Boavista revealed the existence of more material of this type in nests of other coastal areas (Ponta do Sol-Rotchinha NW, Abrolhal N-NE, and Varandinha W), which were characterized, as was the region near the first nest, by the presence of active dunes and adjacent fossil dunes. For example, six of the twelve active and old nests known at Ponta do Sol had rhizoliths incorporated into their structure. The masses and lengths (mean 6 SD) of 50 rhizoliths from one of these nests were respectively 185 6 100.9 g (range 37–437 g) and 195.6 6 56.9 mm (range 114– 353 mm). Although it is likely that the appearance of the concretions, simulating dry sticks and branches, is the sole reason Ospreys collect them, the use of this material reinforces the nest. Even if the rest of nest material vanishes, the rigidity of these rhizoliths ensures their durability over time, and such mounds may provide a stimulus for future Osprey pairs when nest building (Fig. 1b). Moreover, thanks to the presence of these characteristic remains accumulated on cliff ledges, coastal platforms, etc., breeding sites can be identified, thus providing a means by which to estimate past population size and distribution. We would like to thank Pedro Felipe (Alas Cinematografı́a S.L.) for facilitating the journey to Cape Verde in 2001 and Rubén Barone for his constant assistance. Thanks are also due to Manuel Siverio, Luı́s Palma, and Rafel Triay for their helpful review of the initial manuscript and to Pauline Agnew for translating the original into English. Cheryl Dykstra and three anonymous reviewers also made useful comments.—Felipe Siverio (e-mail address: felipe.siverio@ telefonica.net), c/ Los Barros 21, E-38410 Los Realejos, Tenerife, Canary Islands, Spain; Pedro López, C.P. 100, Sal Rei, Boavista, Republic of Cape Verde; and Domingo Trujillo, c/ José Betancor Cabrera 20, 38410 Los Realejos, Canary Islands, Spain.