Browsing by Author "JIMENEZ, JE"
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- ItemBEHAVIORAL ECOLOGY OF GREY EAGLE-BUZZARDS, GERANOAETUS-MELANOLEUCUS, IN CENTRAL CHILE(1989) JIMENEZ, JE; JAKSIC, FMThroughout 1 year we observed the behavioral ecology of Grey Eagle-Buzzards (Geranoaetus melanoleucus) in central Chile. The eagles'' activity period was bimodal, with peaks in mid-morning and mid-afternoon. During the day they spent most of their time flying (except during winter), extensively soaring in thermal and wind updrafts, rarely using flapping flight. Eagles appeared to select specific physiographic features that favored the presence of updrafts, particularly north- and west-facing slopes and ridge tops. Use of these features apparently was unrelated to prey abundance or vegetative cover. Prey were primarily large-sized small mammals, and secondarily reptiles and birds. Although aggressive, eagles were attacked by a number of species of other raptors. Comparison of the behavioral ecology of eagles and of Nearctic buteonines demonstrated some marked differences, particularly in activity time and habitat use. These differences appear to be related to weather conditions prevailing in montane vs. lowland terrain.
- ItemBIOLOGY OF THE AUSTRAL PYGMY-OWL(1989) JIMENEZ, JE; JAKSIC, FMScattered information on the Austral Pygmy-Owl (Glaucidium nanum), published mostly in Argentine and Chilean journals and books of restricted circulation, is summarized and supplemented with field observations made by the authors. Information presented and discussed includes: taxonomy, morphometry, distribution, habitat, migration, abundance, conservation, reproduction, activity, vocalization, behavior, and diet. The first quantitative assessment of the Austral Pygmy-Owl''s food habits is presented, based on 780 prey items from a single central Chilean locality. Their food is made up of insects (50% by number), mammals (32%), and birds (14%). The biomass contribution, however, is strongly skewed toward small mammals and secondarily toward birds.
- ItemBODY-SIZE OF CHILEAN FOXES - A NEW PATTERN IN LIGHT OF NEW DATA(1995) JIMENEZ, JE; YANEZ, JL; TABILO, EL; JAKSIC, FMBy using body measurements and weight data of culpeo fox Dusicyon culpaeus Molina, 1782 and chilla fox D. griseus Gray, 1837 from the Chinchilla National Reserve (north-central Chile) and Torres del Paine National Park (southern Chile), the body size distribution of Chilean foxes was analyzed and compared to data previously published by Fuentes and Jaksic (1979). Contrary to those authors, our data show that not only the larger but both species increase in size in southern Chile. Thus, latitudinal size distribution of D. culpaeus and D. griseus may not be the result of character displacement through exploitation competition, as previously interpreted, but of bioenergetic adaptations.
- ItemCOMPARATIVE ECOLOGY OF DARWIN FOX (PSEUDALOPEX-FULVIPES) IN MAINLAND AND ISLAND SETTINGS OF SOUTHERN CHILE(1990) JIMENEZ, JE; MARQUET, PA; MEDEL, RG; JAKSIC, FMUsing comparable techniques we studied the abundance, habitat use, and diet of Darwin's fox (Pseudalopex fulvipes), as well as prey availability in two constrasting settings of southern Chile: on the mainland in the Nahuelbuta ranges, and in Chiloe Island. This fox lives in sympatry with its congener P. griseus in Nahuelbuta, but is the sole fox on Chiloe Island. We estimated that Darwin's fox is about twice as abundant in Chiloe than on the mainland. The structure of the habitat where Darwin's fox was found was remarkably similar between the two study sites despite floristic differences. Its diet, however, was markedly dissimilar, with mainland foxes preying extensively on mammals and reptiles and little on insects, and island foxes preying primarily on insects and amphibians, and little on mammals. The low consumption of mammals in Chiloe may be attributed to the low densities reached by that prey on the island as compared to Nahuelbuta (estimated at about double the insular density). Fruit consumption in Chiloe was almost three times higher than in Nahuelbuta, suggesting a lower energy diet for insular foxes. We also report behavioural observations on Darwin's fox provided by knowledgeable sources.
- ItemDIET SHIFTS OF BLACK-CHESTED EAGLES (GERANOAETUS-MELANOLEUCUS) FROM NATIVE PREY TO EUROPEAN RABBITS IN CHILE(1992) PAVEZ, EF; GONZALEZ, CA; JIMENEZ, JEFor two years we studied the feeding ecology of Black-chested Eagles (Geranoaetus melanoleucus) in San Carlos de Apoquindo, central Chile. We estimated the diet of eagles using three different methods and evaluated the abundance of introduced European Rabbits (Oryctolagus cuniculus) throughout one year. Eagles preyed in decreasing order of frequency on mammals, reptiles, insects and birds. The biomass component of insects in the diet was negligible. At the species level, the European Rabbit was the most frequently consumed prey (43.9% by number and 81.7% by biomass). The diet composition changed only slightly throughout the year. During non-breeding seasons birds and insects were not consumed. Depending on the technique used, we found differences in the estimated diet. Birds were underestimated and insects were overestimated by direct observations of prey captures and transportations. In contrast, insects were underestimated by the analysis of prey remains. At the class level, the analysis of regurgitated pellets seems to represent the diet of eagles better. European Rabbits were present throughout the year in the study site, peaking during the eagles' breeding season, when kittens were abundant. Eagles preyed preferentially on small rabbits and apparently avoided large individuals. Eagles have increased their consumption of European Rabbits over time as did foxes in the study area.
- ItemDISCOVERY OF A CONTINENTAL POPULATION OF THE RARE DARWIN FOX, DUSICYON-FULVIPES (MARTIN, 1837) IN CHILE(1990) MEDEL, RG; JIMENEZ, JE; JAKSIC, FM; YANEZ, JL; ARMESTO, JJThe rare Darwin''s fox Dusicyon Fulvipes (Martin, 1837) was thought to be restricted to Chiloe Island in southern Chile, and to be a subspecies of Dusicyon griseus. We report the findings of a continential population of D. fulvipes, 600 km north of its known insular ranges and in sympatry with D. griseus. We document for the first time the food habits of Darwin''s fox, add new information on its morphometry, and discuss the systematic, zoogeographic and ecological implications of the discovery of the continental population.
- ItemECOLOGY AND BEHAVIOR OF SOUTHERN SOUTH-AMERICAN CINEREOUS HARRIERS, CIRCUS-CINEREUS(1988) JIMENEZ, JE; JAKSIC, FMWe report field observations made in Torres del Paine National Park, southernmost Chile, on the ecology and behavior of breeding cinereous harriers (Circus cinereus) and summarize scattered information on the biology of this species. Information is presented and discussed on: taxonomy, morphology, distribution, habitat, migration, abundance, status, reproduction, behavior, and diet. Reproductive aspects of the population studied are documented with emphasis on behavior; 1620 min of observations on prey transport and transfer are analyzed quantitatively. The first quantitative assessment of the cinereous harrier''s diet is also presented, based on 1259 prey items identified among 413 regurgitated pellets collected in the study site: 33.6% of the prey (by number) was insects, 27.2% birds, 19.1% each, mammals and reptiles, and 1.0% arachnids. The biomass contribution to the diet, however, follows a decreasing order from birds, through mammals, reptiles, insects, and to arachnids.
- ItemEXPERIMENTAL-EVIDENCE THAT HIGH POPULATION FREQUENCIES OF LIZARD TAIL AUTOTOMY INDICATE INEFFICIENT PREDATION(1988) MEDEL, RG; JIMENEZ, JE; FOX, SF; JAKSIC, FMFrequency of autotomized tails in lizard populations has been taken as an indicator of predation pressure upon those populations. However, recent correlational evidence points to autotomy as reflecting lizards'' escape efficiencies and/or predators'' attack inefficiencies. We report experimental evidence on the relative inefficiencies of three predator species (a teiid, a snake, and a falcon) as autotomy-producing agents, and on the relative escape efficiencies of three congeneric lizard species under laboratory conditions. The falcon was the least inefficient lizard predator (100% of successful attacks) whereas the teiid and snake were more inefficient (10-20% of the lizards escaped by autotomizing their tail). Lizards that successfully escaped predation by the widely-foraging teiid had relatively longer tails than unsuccessful ones. No difference in this feature was detected between successful and unsuccessful lizards attacked by the sit-and-wait snake. All three lizard species were equally efficient at escaping the three predators through tail autotomy. Our observed differences of comparative inefficiencies of lizard predators give experimental support to assertions that tail-loss frequencies do not adequately serve as indices of presumed predatation pressure. High rates of tail-loss among lizard populaions could instead reflect attempts at predation by inefficient predators.
- ItemNUMERICAL AND FUNCTIONAL-RESPONSE OF PREDATORS TO A LONG-TERM DECLINE IN MAMMALIAN PREY AT A SEMIARID NEOTROPICAL SITE(1992) JAKSIC, FM; JIMENEZ, JE; CASTRO, SA; FEINSINGER, POccurrence and diet of ten carnivorous predators (four falconiforms, four owls, and two foxes), and population levels of their mammalian prey, were monitored over 45 months at a semi-arid site in north-central Chile. Early in this period, small mammals irrupted and then declined markedly to a density 7% of that at peak. All four falconiforms (Buteo polyosoma, Falco sparverius, Geranoaetus melanoleucus, Parabuteo unicinctus) and one owl (Tyto alba) responded numerically to the decline in mammalian prey by virtually abandoning the study site. The three other owls (Athene cunicularia, Bubo virginianus, Glaucidium nanum) and the two foxes (Pseudalopex culpaeus and P. griseus) remained. With few exceptions, throughout the study predators maintained species-specific preferences among small mammal species regardless of the absolute and proportional abundance of these prey. At no time did the two prey species most responsible for the irruption (the rodents Phyllotis darwini and Akodon olivaceus) occur in predators' diets out of proportion to their estimated relative abundance in the field. Predators were clearly unable to prevent the irruption from occurring. Given the absence of a clear functional response to the most irruptive species, predators seemed unlikely to have been responsible for the observed crash. At present, however, predators may be prolonging the crash and delaying the return of small-mammal populations to typical densities.
- ItemOBSERVATIONS ON THE COMPARATIVE BEHAVIORAL ECOLOGY OF HARRIS HAWK IN CENTRAL CHILE(1993) JIMENEZ, JE; JAKSIC, FMThroughout one year we observed the behavioral ecology of Harris' Hawks (Parabuteo unicinctus) in central Chile. The hawks' activity period lacked diel or annual variation. Their most common flight mode was soaring in thermals and wind updrafts, rarely using flapping flight, and never hovering. Harris' Hawks appeared to select physiographic features that favored the presence of updrafts, particularly north- and west-facing slopes and ridgetops, but were also commonly seen flying over ravines (where they perched frequently). Prey were primarily small- and medium-sized mammals, and secondarily medium-sized birds. Although not aggressive, Harris' Hawks were nonetheless attacked by two other sympatric raptors, Black-chested Eagles (Geranoaetus melanoleucus) and Red-backed Hawks (Buteo polyosoma). These three species, which were studied over the same period and with the same techniques, were similar in activity and behavior, although Harris' Hawks were slightly more different than the latter were between themselves.
- ItemSPATIOTEMPORAL PATTERNS OF AN IRRUPTION AND DECLINE OF SMALL MAMMALS IN NORTHCENTRAL CHILE(1992) JIMENEZ, JE; FEINSINGER, P; JAKSIC, FMDuring the austral winter of 1987 (June-August) at a semi-arid site in northcentral Chile, an outbreak of small mammals apparently was triggered by one episode of unusually high rainfall. From October 1987 to November 1990, we monitored the outbreak on a monthly basis on two equatorial- and two polar-facing slopes. Overall density on equatorial-facing slopes was 239 individuals/ha in spring 1987, increasing to a peak of 404/ha by summer 1988, and then steadily declining to a crash of 20/ha (5% of peak density) by spring 1990, with no signs of recovery. On polar-facing slopes, mammalian abundances were about one-half those of equatorial-facing slopes. There were 112 individuals/ha in spring 1987, increasing to a peak of 199/ha by summer 1988, and then steadily declining to a crash of 8/ha (4% of peak density) by spring 1989. Since then, mammal populations on polar-facing slopes have been slowly recovering, reaching 11% of their peak density by November 1990. Of the eight species monitored, only three irrupted: the granivorous cricetid Phyllotis darwini, the omnivorous cricetid Akodon olivaceus, and the insectivorous didelphid Marmosa elegans. These three irrupted and declined in phase, simultaneously on the two opposite-facing slopes, such that their relative frequencies did not shift markedly. Two of the three folivores (Abrocoma bennettii, Octodon degus, but not Chinchilla lanigera), one granivore (Oryzomys longicaudatus), and one insectivore (Akodon longipilis) disappeared from the site, persisting longer on equatorial-facing slopes.