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1

Eurasian otter (Lutra lutra) density estimate based on radio tracking and other data sources

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Quaglietta L., Hajkova P., Mira A., Boitani L.
Acta Theriologica
|
2015
|
tom 60
|
nr 2
Estimating animal population size is a critical task in both wildlife management and conservation biology. Precise and unbiased estimates are nonetheless mostly difficult to obtain, as estimates based on abundance over unit area are frequently inflated due to the “edge effect” bias. This may lead to the implementation of inappropriate management and conservation decisions. In an attempt to obtain an as accurate and conservative as possible picture of Eurasian otter (Lutra lutra) numbers, we combined radio tracking data from a subset of tracked individuals from an extensive project on otter ecology performed in Southern Portugal with information stemming from other data sources, including trapping, carcasses, direct observation of tagged and untagged individuals, relatedness estimates among genotyped individuals, and a minor contribution from non-invasive genetic sampling. In 158 km of water network, which covers a sampling area of 161 km2 and corresponds to the minimum convex polygon constructed around the locations of five radio-tracked females, 21 animals were estimated to exist. They included the five radio-tracked, reproducing females and six adult males. Density estimates varied from one otter per 3.71–7.80 km of river length (one adult otter per 7.09–14.36 km) to one otter per 7.67–7.93 km2 of range, depending on the method and scale of analysis. Possible biases and implications of methods used for estimating density of otters and other organisms living in linear habitats are highlighted, providing recommendations on the issue.
2

Factors affecting the distribution of Sorex samniticus, an endemic Italian shrew, in an heterogeneous landscape

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Mortelliti A., Amori G., Sammuri G., Boitani L.
Acta Theriologica
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2007
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tom 52
|
nr 1
We studied the factors affecting the distribution of an endemic shrewSorex samniticus Altobello, 1926 in the Province of Siena, central Italy. Distribution data were obtained by examining pellets from 31 barn owlTyto alba sites (roosts) over a period spanning from 1974 to 2005. We constructed a model using logistic regression analysis on presence/absence data. Results show that an increase in forest dominated byQuercus cerris andCastanea sativa led to the local extinction of this species. Results were confirmed through the examination of one box, with 3044 prey items deposited in layers, that documents the expansion of the species in that area following increased logging ofQuercus cerris andCastanea sativa forests. Cessation of logging has again led to the absence of the species from the area. We discuss these results from the perspective of ecological network planning, showing that utilisation of non-detailed maps, such as Corine Land Cover, that do not distinguish between the various kind of broadleaved forests is inadequate to describe the finer grade of habitat selection of this small mammal.
3

Survey of an otter Lutra lutra population in Southern Italy: site occupancy and influence of sampling season on species detection

100%
Fusillo R., Marcelli M., Boitani L.
Acta Theriologica
|
2007
|
tom 52
|
nr 3
In order to assess the current status of the otterLutra lutra Linnaeus, 1758 in Southern Campania (Italy), we surveyed 141 sites for spraints (faeces) in 2001. Fifty-eight sites were surveyed during the winter and in the following summer in order to test, through an estimation-based approach, the influence of sampling season on species detection. Site occupation in the study area was high (69.5%) and possibly underestimated, because the survey was affected by non-detection errors. Our analyses showed that winter surveying markedly underestimated true otter occupancy at the 58 sites (51.7% vs 97.1%), whereas summer surveying was very reliable (91.4%). Rains and floods may have removed spraints during winter, thereby reducing the detection probability to 0.534. These results suggest that otter standard surveys in areas with Mediterranean-type climates should be conducted during summer or periods without prolonged precipitation. Comparing our results with those of the 1985 National survey, we found an occupancy increase from 65.8 to 100%. We could not establish whether this change reflected a population increase or was due to possible non-detection errors that occurred in the 1985 survey. However, the present occupancy substantiates the strategic relevance of the study area for planning the conservation of Italian otters.
4

Weasel Mustela nivalis spatial ranging behaviour and habitat selection in agricultural landscape

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Magrini C., Manzo E., Zapponi L., Angelici F. M., Boitani L., Cento M.
Acta Theriologica
|
2009
|
tom 54
|
nr 2
137-146
This paper reports the findings of a study on the spacing pattern of a population of weaselsMustela nivalis Linnaeus, 1758 in central Italy. We describe this pattern at spatial and habitat level, meant as a set of vegetational and environmental features. The study area is a typical agricultural landscape, consisting of highly fragmented natural habitat modified by thousands of years of human presence and work. The results indicate that individual home ranges vary greatly from non breeding to breeding season: during spring and summer, weasels increase their movements and the number of tracts they cross, which results in home range areas up to 10 times larger. Moreover this study demonstrates a strong preference of weasels for habitats formed by natural residual edges between fields and meadows. The shapes of the individual home ranges follow these edges, producing a typical linear spatial home range pattern.
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