Browsing by Author "Castro, SA"

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    Effects of bird ingestion on seed germination of four woody species of the temperate rainforest of Chiloe island, Chile
    (2002) Figueroa, JA; Castro, SA
    We study the effect of ingestion by birds on seed germination and the consequences of absence of dispersal, with the persistency of the seeds inside the fruit. We collected seeds of four woody species of the temperate rainforest of Chiloe: Gaultheria mucronata, Luma apiculata, Myrteola nummularia, and Myrceugenia planipes. The seeds tested had the following origins: 1) Ingested seeds: seeds collected from the feces of birds, 2) Extracted seeds: seeds obtained directly from the fruits, and 3) Intact fruits: fruits collected directly from the plants. Germination of Myrceugenia planipes under greenhouse conditions, Luma apiculata, and Myrteola nummularia under laboratory conditions, and Gaultheria mucronata under both conditions was analyzed. We found that the seeds reach their maximum germination between 15-20 days after sowing, with the exception of those of G. mucronata sown in the greenhouse, which showed a low germination rate. In the greenhouse assay, seeds of G. mucronata ingested by birds, seeds extracted manually from the fruits, and seeds inside the fruits did not show significant differences in their germination percentages. In the laboratory assays, the seeds of G. mucronata and M. nummularia ingested by birds and the seeds extracted manually from the fruits also did not show any significant difference in germination. Under laboratory conditions, the seeds of L. apiculata ingested by birds presented a statistically greater percentage of germination than the seeds extracted manually. Under greenhouse conditions, seeds of M. planipes ingested by birds did not present a statistically different germination percentage from those seeds extracted from the fruits. The seeds of M. planipes, and L. apiculata inside the intact fruits did not germinate. We conclude that birds do not affect the seed viability of any of the four species studied.
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    Great horned and barn owls prey differentially according to the age size of a rodent in northcentral Chile
    (1995) Castro, SA; Jaksic, FM
    Based on cranial measurements we estimated the size- and age-class (juvenile or adult) of leaf-eared mice (Phyllotis darwini) consumed by great horned (Bubo virginianus) and barn owls (Tyto alba) during 1990-92 in a semiarid locality of northcentral Chile. We compared this information to that obtained from mice live-trapped at the same place and period. The frequency distributions of body weights of leaf-eared mice consumed by the two owl species was not statistically different, despite the four-fold difference in body size and different hunting mode of the two owls. In two out of three breeding seasons the owls preyed more frequently on adult mice. In the remaining breeding season and the three wintering seasons they preyed upon adults and juveniles in about the same proportion as they were live-trapped in the field. The higher predation on adult individuals (reproductive) was associated to a greater mobility of adult versus juvenile mice, which may render the former more vulnerable to owl detection.