Jacques Bovet

Social synchronization of circadian rhythms in deer mice (Peromyscus maniculatus)

SummaryDeer mice (Peromyscus maniculatus), kept in individual cages under constant dim-light conditions, displayed steady free-running rhythms of activity, the period of which varied between individuals.When two previously isolated mice with different rhythms were placed in a common enclosure, under the same constant light conditions, they soon displayed a mutual synchronization of their activity rhythms. When separated again, the mice lost mutual synchronization (Figs. 1 and 2)The process by which mutual synchronization was attained in the common enclosure is typical of entrainment by an external synchronizer (Zeitgeber). Our results suggest that the activity rhythm of the dominant mouse entrains the activity rhythm of the subordinate, and is thus a ‘social Zeitgeber.’

Free-running circadian activity rhythms in free-living beaver (Castor canadensis)

SummaryThe members of a beaver family studied under natural conditions in SW Alberta, Canada (115 °03′ W, 51 °02′ N) displayed a free-running circadian rhythm of activity with a period length of about 27 hours in winter, at a time when they were living under ice and had no access to land (Fig. 1, A and C). In summer, the period length of their activity rhythm was close to 24 hours (Fig. 1, B).

Annual cycle of patterns of activity rhythms in beaver colonies (Castor canadensis)

SummaryBeavers studied under natural conditions near Québec City, Canada, displayed a yearly cycle of patterns of activity rhythms. In winter, the beaver colonies had a free-running circadian rhythm of period length 26.25 to 28.0 h, with or without relative coordination, depending on available light intensity, which in turn depends on ice and snow cover conditions; in summer, their activity rhythm followed a “normal” 24 h period. Transitions between these two patterns suggest that annual variations in the beavers physiological state affect their reaction towards the presence or absence of a Zeitgeber.

Homing in Wild Myomorph Rodents: Current Problems

Authors currently disagree as to whether random scatter, familiarity with a large area, or navigation is the basic mechanism of homing in rodents. Starting from the behavior of animals that fail to home, I present a new hypothesis based on motivational factors, which could explain the observed decreases of homing success that occur with increasing distances in rodents and other animals, irrespective of the possible mechanisms involved. I also suggest that consideration of the behavior of nonhomers is essential in attempts to explain homing.

Orientation strategies for long distance travel in terrestrial mammals, including humans

The accurate mapping of routes taken by North American red squirrels in their spontaneous or experimentally induced long distance travels suggests tactics and strategies involving route-based orientation, systematic search and a minimal load on the working and reference memories of the animals. Straightness of travel and independence between direction-to-goal and distance-to-goal estimations are claimed to be key elements in the process. The results of pilot experiments on the «homing» behavior of humans fit well into this conceptual framework.

Homing in humans: A different look.

A current model holds that the long-distance homing abilities of free-ranging mammals rest primarily on a strategy of course reversal, based on outward journey information. In this study, I measured the ability to orient toward home in humans displaced under conditions that promote the use of this strategy, namely along an outward route that was direct, and the main bearing of which could be extrapolated by reference to a pre-existant mental map and by visual backup during the outward journey. Even though the individual course estimates obtained did show a certain amount of dispersion and/or error, they were more accurate and less dispersed than in experiments by other authors, where subjects could not use this strategy, because they were displaced blindfolded and/or along circuitous routes.

Cognitive Map Size and Homing Behavior

A map provides information on the spatial relationships that exist between any two points X and Y that are on it. The simplest of these relationships can be expressed as \(\overline {{\rm{XY}}} \), the straight line segment between X and Y, characterized by a certain length, and a certain angular deviation from an axis of reference (e.g., the South-North axis). If the sense of this relationship is specified, e.g. from X (as an initial point) to Y (as a terminal point), then the segment \(\overline {{\rm{XY}}} \) becomes the vector\(\overrightarrow {{\rm{XY}}} \) of the same length, with a certain direction with respect to a bearing of reference (e.g., North). Common sense indicates that if you have to travel from X to Y along the most direct route, it is not necessary to make use of, or even to know the length of vector \(\overrightarrow {{\rm{XY}}} \): if the map tells you the orientation of the vector with respect to North and if you are able to transpose this orientation to the real world situation (e.g., using a compass), then you have just to follow the due course until you inevitably hit Y. If you use this procedure and want to stop at Y, however, you obviously need to be able to detect a signal at Y that tells you that you have reached your goal. The important point here is that this signal is totally independent of the distance between X and Y.