Swimming behavior and performance of the marsh rat Holochilus vulpinus (Brants, 1827) (Cricetidae, Sigmodontinae)

Semiaquatic habits evolved in several Sigmodontinae rodent species, but this issue remains poorly studied. The marsh rat Holochilus vulpinus (Brants, 1827) has been associated with palustrine wetland environments and exhibits several morphological traits related to the semiaquatic habit. However, its swimming behavior and the way its morphological specializations contribute to it have not been evaluated so far in this species. This note focuses on describing and quantifying the swimming behavior and swimming performance of H. vulpinus. In order to address these issues, five individuals of H. vulpinus, four adults and one subadult, were filmed while swimming and their performance was quantified. The obtained results indicate that the swimming mode is bipedal paddling, alternating the stroke of the hind feet. The quantitative indicators also qualify H. vulpinus as a good swimmer compared to other terrestrial and semiaquatic mammals.

NEW METHODS FOR STUDYING THE ACTIVITY OF SEMIAQUATIC MAMMALS

A new method for studying the activity of semiaquatic mammals using digital portable voice recorders has been developed. Previously, actographs and night-vision devices were used to study semiaquatic mammals near their burrows. This method allows the mammal activity registration directly in the burrows. The use of voice recorders makes it possible to accurately determine whether the burrow system is inhabited or non-inhabited. In addition, it has become possible to identify the day-night time intervals during which the animals are the most or least active. The new method was tested on the Russian desman (Desmana moschata). Therefore, to identify the burrows in which the recorders were to be installed, the burrows were probed. A probe is a pole pointed at one end with a T-shaped handle at the other end. The researcher's task is to detect the entrance to the burrow, usually under water. And then the direction of the underground passage is determined by means of the probe. For this purpose, the ground is pierced to detect the hollows in the burrow with the probe starting from the burrow entrance (the probe falls through unevenly). At a distance of 2–3 meters from the burrow, in some cases largely depending on the burrow length, the ground is dug up above the burrow in the form of a small well, 10–15 cm in diameter. A digital voice recorder was placed vertically in this well, so that the microphone was directed down towards the burrow. Desman noises can be characterized as short series formed as a sequence of contiguous short peaks of 15–25 seconds with 5 second interruptions formed by regular waves of breathing and its movement noises. Desman noises differ by mean amplitude and duration on oscillograms. As a rule, the noise audibility ranges from 1 to 3 minutes.

Eye Optics in Semiaquatic Mammals for Aerial and Aquatic Vision

Based on anatomical measurements of refractive structures in the eye, the positions of focused images were computed for several groups of semiaquatic mammals: rodents, a nonpinniped semiaquatic carnivore (the sea otter), and pinniped carnivores (seals, sea lions, and the walrus). In semiaquatic rodents, eye optics enable emmetropia in the air but cause substantial hypermetropia in the water. In semiaquatic carnivores, there are several mechanisms for amphibious vision that focus images on the retina in both air and water. These mechanisms include the potential for a substantial change in the lens shape of sea otters and the presence of the corneal emmetropic window in pinnipeds. The results suggest that several groups of mammals that independently adapted to aquatic environments vary in how their visual systems adapted to aquatic vision.

Considerations on the vulnerability of the Eurasian water shrew Neomys fodiens to the presence of introduced brown trout Salmo trutta

Introduced fish represent a major threat for aquatic ecosystems and species and their impact on semiaquatic vertebrates, such as amphibians, has been extensively studied. On the other hand, little is known about their impact on semiaquatic mammals, such as water shrews (