A major difficulty in the application of probabilistic models to estimations of mammal abundance is obtaining a data set that meets all of the assumptions of the model. In this paper, we evaluated the concordance correlation among three population size estimators, the minimum number alive (MNA), jackknife and the model suggested by the selection algorithm in CAPTURE (the best-fit model), using long-term data on three Brazilian small mammal species obtained from three different studies. The concordance correlation coefficients between the abundance estimates indicated that the probabilistic and enumeration estimators were highly correlated, giving concordant population estimates, except for one species in one of the studies. The results indicate the adequacy of using enumeration estimates as indexes for population size when scarce data do not allow for the use of probabilistic methods. Differences observed in the behavior of enumeration and probabilistic methods among species and studies can be related to the exclusive sampling design of each area, species-specific movement characteristics and whether a significant portion of the population could be sampled.

A fundamental step in the emerging Movement Theory is the description of movement paths, and the identification of its proximate and ultimate drivers. The most common characteristic used to describe and analyze movement paths is its tortuosity, and a variety of tortuosity indices have been proposed in different theoretical or empirical contexts. Here we review conceptual differences between five movement indices and their bias due to locations errors, sample sizes and scale-dependency: Intensity of Habitat use (IU), Fractal D, MSD (Mean Squared Distance), Straightness (ST), and Sinuosity (SI). Intensity of Habitat use and ST are straightforward to compute, but ST is actually an unbiased estimator of oriented search and ballistic movements. Fractal D is less straightforward to compute and represents an index of propensity to cover the plane, whereas IU is the only completely empirical of the three. These three indices could be used to identify different phases of path, and their path tortuosity is a dimensionless feature of the path, depending mostly on path shape, not on the unit of measurement. This concept of tortuosity differs from a concept implied in the sinuosity of BENHAMOU (2004), where a specific random walk movement model is assumed, and diffusion distance is a function of path length and turning angles, requiring their inclusion in a measure of sinuosity. MSD should be used as a diagnostic tool of random walk paths rather than an index of tortuosity. Bias due to location errors, sample size and scale, differs between the indices, as well as the concept of tortuosity implied. These differences must be considered when choosing the most appropriate index.

Relatamos o primeiro registro de comportamento de "homing" de um marsupial neotropical, Philander frenatus. O indivíduo estudado retornou para o fragmento onde foi capturado (distante 1050 m) atravessando uma matriz hostil, ao invés de se deslocar para um fragmento muito mais próximo (distante 50 m). Os movimentos não seguiram a direção do vento ou do fragmento mais próximo, sendo significativamente orientados para o fragmento de captura. O indivíduo provavelmente tinha experiência prévia com o local de soltura. Este registro sugere que a habilidade de P. frenatus de tolerar os efeitos da fragmentação de habitat pode ser maior do que considerada previamente.

We report the first record of homing behavior of a Neotropical marsupial, the opossum Philander frenatus. The individual studied returned to the home forest fragment where it was captured (1050 m away) crossing a hostile matrix, instead moving to a much closer fragment (50 m distant). Movements did not follow wind or the direction of the closest fragment, but they were significantly oriented towards the home fragment. The individual probably had previous experience with the release site. This unique observation suggests that the ability of P. frenatus to overcome the effects of habitat fragmentation may be higher than considered previously.

Uma população de gambás, Didelphis aurita Wied-Neuwied 1826, foi estudada de 1997 a 2006 por captura, marcação e recaptura numa área de Mata Atlântica no Estado do Rio de Janeiro. Foram estabelecidas coortes, incluindo apenas fêmeas marcadas ainda no marsúpio, classificando-as em cinco classes etárias. Os parâmetros populacionais foram calculados através de tábuas de vida horizontais. A maior mortalidade ocorreu entre as classes etárias I e II, logo após o desmame, sendo que a sobrevivência apresentou uma curva do tipo III. A taxa de fecundidade foi inversamente correlacionada com a sobrevida, o valor reprodutivo inversamente correlacionado com a mortalidade e o valor reprodutivo residual inversamente correlacionado com a taxa de fecundidade. A taxa intrínseca de crescimento sempre esteve próxima de zero, porem ligeiramente negativa. O gambá mostrou-se um bom modelo de mamífero para este tipo de estudo.

A population of the black-eared opossum, Didelphis aurita Wied-Neuwied 1826, was studied during 1997-2006 by capture-mark-recapture in the Atlantic Forest in the state of Rio de Janeiro. Cohorts were established with females marked still in the pouch, classified into five age classes. Population parameters were estimated using life tables. Survival was type III and mortality was greatest in age classes I and II, just after weaning. Fecundity was inversely correlated with survival, reproductive value was inversely correlated with mortality and residual reproductive value was inversely correlated with fecundity. The intrinsic rate of increase was always close to zero and tended to be slightly negative. The black-eared opossum can be considered a good model species for this type of study.