José Hernán Sarasola

Reduced MHC and neutral variation in the Galapagos hawk, an island endemic

BackgroundGenes at the major histocompatibility complex (MHC) are known for high levels of polymorphism maintained by balancing selection. In small or bottlenecked populations, however, genetic drift may be strong enough to overwhelm the effect of balancing selection, resulting in reduced MHC variability. In this study we investigated MHC evolution in two recently diverged bird species: the endemic Galápagos hawk (Buteo galapagoensis), which occurs in small, isolated island populations, and its widespread mainland relative, the Swainsons hawk (B. swainsoni).ResultsWe amplified at least two MHC class II B gene copies in each species. We recovered only three different sequences from 32 Galápagos hawks, while we amplified 20 unique sequences in 20 Swainsons hawks. Most of the sequences clustered into two groups in a phylogenetic network, with one group likely representing pseudogenes or nonclassical loci. Neutral genetic diversity at 17 microsatellite loci was also reduced in the Galápagos hawk compared to the Swainsons hawk.ConclusionsThe corresponding loss in neutral diversity suggests that the reduced variability present at Galápagos hawk MHC class II B genes compared to the Swainsons hawk is primarily due to a founder event followed by ongoing genetic drift in small populations. However, purifying selection could also explain the low number of MHC alleles present. This lack of variation at genes involved in the adaptive immune response could be cause for concern should novel diseases reach the archipelago.

Past and current evidence of persecution of the Endangered crowned eagle Harpyhaliaetus coronatus in Argentina

The crowned eagle Harpyhaliaetus coronatus is a large Neotropical eagle categorized as Endangered throughout its range. However, the threats to this species are poorly understood. We present data on the causes of death of crowned eagles in semi-arid forests of La Pampa province, central Argentina. Data was obtained from field surveys and from interviews with 62 local landowners during 1999–2004. Over this period five eagles were shot, one killed by a car, one was found dead in a cattle water trough, and one was found in captivity. From the interviews information was obtained about a further 10 cases of eagles being shot, disturbed or trapped. Five (13%) of 38 interviewed landowners who positively identified the species admitted having killed or disturbed eagles in the past but only two (5%) mentioned predation of eagles upon livestock as a problem. Persecution seems to be a significant threat to this species in central Argentina and future research and conservation action should be focused not only on gaining a better knowledge of the biology of the species but also on conservation and educational programmes involving local people.

MOLECULAR AND MORPHOLOGICAL DIVERGENCE IN A PAIR OF BIRD SPECIES AND THEIR ECTOPARASITES

Abstract In an evolutionary context, parasites tend to be morphologically conservative relative to their hosts. However, the rate of neutral molecular evolution across many parasite lineages is faster than in their hosts. Although this relationship is apparent at the macroevolutionary scale, insight into the processes underpinning it may be gained through investigations at the microevolutionary scale. Birds and their ectoparasitic lice have served as important natural experiments in co-evolution. Here, we compared mitochondrial and morphological divergence in 2 recently diverged avian host lineages and their parasites. Gálapagos hawks (Buteo galapagoensis) are phenotypically divergent from their closest mainland relatives, the Swainsons hawk (Buteo swainsoni). Both species are host to a feather louse species of Craspedorrhynchus (Insecta: Phthiraptera: Ischnocera, Philopteridae). We sequenced the 5′ end of the mitochondrial gene cytochrome oxidase c subunit I (COI) from a set of hawks and lice. Although this fragment allowed unambiguous identification of host and parasite lineages on the islands and the mainland, only a single variable site was present in the 2 hosts, but 2 major Craspedorrhynchus clades divergent by ∼10% were recovered that sorted perfectly with host species. We found significant population genetic structure within the Galápagos Craspedorrhynchus lineage. While the host species are highly differentiated phenotypically, the 2 Craspedorrhynchus louse lineages are phenotypically overlapping, although subtle but significant morphological differences exist.

Breeding season habitat selection by Ferruginous Pygmy Owls Glaucidium brasilianum in central Argentina

Capsule The presence of Ferruginous Pygmy Owls Glaucidium brasilianum breeding in the xerophytic forest of Caldén Prosopis caldenia in central Argentina was slightly affected by forest maturity but neither by the structure of vegetation strata at the micro-habitat scale, nor by forest composition (mosaic of forest–grassland or shrubland) or proximity of water bodies at the macro-habitat scale. Aims To assess the habitat characteristics selected by Ferruginous Pygmy Owls during the breeding season. Methods Random transects were performed across a portion of the Luro Natural Reserve by broadcasting Ferruginous Pygmy Owl calls. Locations along these transects were used to carry out a presence/absence habitat analysis at micro- and macro-habitat levels. Results Ferruginous Pygmy Owls were found in the majority of sampled locations. However, their presence was not associated with the vegetation structure and composition around sampled locations. Model outputs suggested similarity among presence and absence locations at both spatial scales, though owls showed a slight preference for areas with older trees and higher edge-density values. Conclusion The Ferruginous Pygmy Owl was more abundant than previously thought in the Caldén xerophytic forest, emphasizing the habitats conservation importance, particularly because of the land-use changes that the La Pampa region is experiencing (e.g. forest exploitation).

Not as Similar as Thought: Sexual Dichromatism in Chimango Caracaras is Expressed in the Exposed Skin but Not in the Plumage

Many of the mechanisms involved in visual signalling in birds are based on pigment-based plumage ornamentation and colouration rather than the expression of other, non-plumage-based displays. We have analysed the colouration of the tarsi and ceres of free-ranging Chimango Caracaras Milvago chimango, a controversial morphological trait for this species, and examined the proximal causes related to the expression of colour in these featherless body parts. The tarsi–ceres of 81 Chimango Caracaras captured in central Argentina between 2005 and 2008 were either yellow–yellow or bluish–pink coloured. Differences in colour were not linked with plasma carotenoid levels and did not vary seasonally. Rather, expression of the two colours was affected by the gender and age of individuals. Yellow-coloured tarsi and ceres were recorded only in adult males, while the remaining age and gender groups showed pinkish- and bluish-coloured bare parts, which is the suspected neutral developmental stage under low hormonal levels. These results support sexual rather than natural selection forces acting on the expression of yellow colouration in the bare parts of adult males. However, an exaggeration of yellowish colour during mating periods in accordance with an increase of circulating carotenoid levels may be expected due to the sexually-related nature of this trait. This documented partitioning of colour variation among sexes and ages that is unrelated to melanin-dependent plumages is unusual and contrary to the most widely observed types of sexual dichromatism in birds.ZusammenfassungViele der Mechanismen für den Austausch visueller Signale bei Vögeln beruhen auf pigmentbasiertem Gefiederschmuck und -farbe statt auf der Zurschaustellung anderer, von den Federn unabhängiger Signale. In unserer Untersuchung analysierten wir die Farbgebung der Tarsi frei lebender Chimangokarakaras (Milvago chimango), einer für diese Art kontrovers beschriebenen morphologischen Eigenheit, und prüften die proximalen Ursachen für die Farbgebung dieser federlosen Körperteile. Die Tarsi-Ceres der 81 zwischen 2005 und 2008 in Argentinien gefangenen Chimangokarakaras waren entweder gelblich oder pink-blau. Die Farbunterschiede zeigten weder einen Zusammenhang mit den Carotinoid-Pegeln im Plasma, noch jahreszeitlich bedingte Unterschiede. Stattdessen gab es einen Zusammenhang mit dem Geschlecht und dem Alter der Tiere. Gelbe Tarsi und Ceres traten nur bei erwachsenen Männchen auf, während diese Körperteile bei den übrigen Geschlechts- und Altersgruppen pink und bläulich waren, dem vermuteten neutralen Entwicklungsstadium bei niedrigen Hormonpegeln. Diese Ergebnisse sprechen eher für einen Geschlechtsunterschied als für einen Selektionsdruck auf die Ausbildung gelber Färbung der federlosen Körperteile ausgewachsener Männchen. Es wäre dann allerdings zu erwarten, dass die gelbe Färbung während der Balzzeit besonders stark ausgeprägt sein würde, zusammen mit einem Anstieg des Karotinoid-Pegels. Im Gegensatz zu der in der Regel beobachteten geschlechtsbedingten Färbung bei Vögeln ist dieses Ergebnis insofern ungewöhnlich, als es eine unterschiedliche Farbgebung bei Geschlechts- und Altersgruppen aufzeigt, die nicht mit der Melanin-abhängigen Gefiederfärbung zusammenhängt.

Parental Care and Behavior of Breeding American Kestrels (Falco sparverius) in Central Argentina

Abstract We studied reproductive parameters, agonistic interactions, foraging behavior, prey deliveries, and diet of American Kestrels (Falco sparverius) using nest boxes in semiarid forests in central Argentina. The breeding season (from egg-laying to fledging) began in late October and ended in late December. Average clutch size was 4.3 ± 0.3 (SE) eggs (N  =  6 nests), hatching success was 73%, and nest success was 66%. Incubation was primarily by females, whereas males mostly hunted and defended the nest area. During early and late nestling stages, both sexes showed aggressive behavior against intruders. The primary hunting method we observed kestrels using near the nest box was perch-hunting (99%), with a peak in hunting activity during midday for females and during morning for males. Both sexes visited the nest most frequently during the late nestling stage (males: 1.04 ± 0.47 prey/hr; females: 1.22 ± 0.35 prey/hr), likely because of high energy demands of the nestlings for growth during that time. The majority of the nestling diet was arthropods (71.4% of diet as determined by observations; 71% by pellets; 89% by prey remains). Reproductive characteristics of this species in the semiarid forest of central Argentina, including reproductive rate, role partitioning between sexes, foraging behavior, and diet, are similar to those previously recorded for some populations in North America.

Comparison of food habits and prey selection of the white‐tailed kite, Elanus leucurus, between natural and disturbed areas in central Argentina

We studied the food habits of white‐tailed kites (Elanus leucurus, Accipitridae) in central Argentina during austral spring and summer (November to March) and compared prey captured in two different habitat types. Diet was determined by analysing pellets and prey remains collected under nests and roost sites. During the same period small mammals were trapped using pit‐fall traps in Parque Luro reserve with the aim of assessing prey selection by kites. In Parque Luro reserve (semiarid forest), tuco‐tucos (Ctenomys sp., Rodentia) were the main prey in the white‐tailed kite diet, accounting for 75% of the items and 91% of biomass. In agricultural fields, however, there was not a single main prey species, as measured either by number of prey items or by biomass, Calomys sp. (43%) and Akodon azarae (22%) being the main prey in this habitat. The analysis of prey availability in the Parque Luro reserve showed that tuco‐tucos are a seasonally available prey, only captured in spring and summer. During these seasons, the consumption of tuco‐tucos by white‐tailed kites was disproportionately higher than the occurrence of tuco‐tucos, indicating a preference for this species by kites. These results suggest that other prey attributes, such as conspicuousness and social behavior, could be key factors in prey selection by white‐tailed kites.

Hailstorms as a Cause of Mass Mortality of Swainson's Hawks in Their Wintering Grounds

We describe a mass mortality event of wintering Swainsons hawks (SH, Buteo swainsoni) in central Argentina during November 2003. One hundred thirteen SH were found dead as a consequence of a single hailstorm. In addition, 14 hawks with severe injuries were recovered alive, but only 10 of these survived 1 wk later. Another 45 dead birds of 11 species were collected in the area. Interviews with local landowners conducted in other areas of the SH wintering grounds provided further evidence of past hailstorm-related mortality involving SH, suggesting that such events commonly occur in the Argentine Pampas. This potential cause of mass mortality of SH wintering in agricultural areas of Argentina may be significant when added to the increased mortality associated with poisoning events during the last decade.

Hypercarnivorous apex predator could provide ecosystem services by dispersing seeds.

Large “hypercarnivorous” felids are recognized for their role as apex predators and hence as key elements in food webs and ecosystem functioning through competition and depredation. Here we show that cougars (Puma concolor), one of the largest and the most widely ranging apex felid predators with a strictly carnivorous diet, could also be effective secondary long distance seed dispersers, potentially establishing direct and non-herbivore mediated interactions with plant species at the bottom of the food web. Cougars accidently ingest and disseminate large amounts of seeds (31,678 seeds in 123 scats) of plant species initially consumed by their main prey, the Eared Dove Zenaida auriculata. The germination potential of seeds for the three plant species most abundantly found in cougar scats (19,570 seeds) was not significantly different from that observed in seeds obtained from dove gizzards, indicating that seed passage through cougar guts did not affect seed germination. Considering the estimated cougar density in our study area, dispersal of seeds by cougars could allow a mean, annual seed spread of ~5,000 seeds per km2. Our results demonstrate that strictly carnivorous, felid predators could have broad and overlooked ecological functions related to ecosystem structuring and functioning.

Nest-Box Occupancy by Neotropical Raptors in a Native Forest of Central Argentina

Abstract Breeding populations of raptors are sometimes limited by nest-site availability and the use of nest boxes to bolster such populations is widespread. In the neotropical forest, little is known about the ecology of cavity-nesting raptors and their use of nest boxes. Here we examine occupancy patterns of nest boxes by five raptor species during eight years in a semiarid forest of central Argentina: the American Kestrel (Falco sparverius), the Spot-winged Falconet (Spiziapteryx circumcincta), the Tropical Screech-Owl (Megascops choliba), the Barn Owl (Tyto alba), and the Ferruginous Pygmy-Owl (Glaucidium brasilianum). We analyze the influence of vegetation type on nest-box selection, report cases of nest usurpation, and present information on the breeding rates of some of these species. The raptor species showed a marked selection for nest boxes surrounded by grassland, where hunting success may be higher, and avoided those nest boxes placed in habitats dominated by dense shrublands. We observed two ...