Vertebrate Behavioral Rhythms

Abstract

INTRODUCTIONInterest in rhythms of animal behavior derives from the recognition that the biological value of a behavior depends as much on when it occurs as on the particular form it takes (see Enright, 1970, and Chapter 15). It follows that a meaningful ethogram of any ~pecies should describe both species-typical motor patterns and species-typical timing of behavior. This chapter surveys the variety of behavioral rhythms that have been studied and the range of species in which they have been described.There are several problems with most of the available descriptions of behavioral rhythmicity. One is analogous to a classical problem in descriptive ethology: that of determining appropriate units of analysis. Ethologists have recognized that significant features of behavior, such as the degree of apparent stereotypy, are to a large extent determined by the temporal and spatial resolution of the recording procedure (Barlow, 1968). Reports of behavioral rhythms have generally ignored this issue and have included data that are grouped in a great variety of ways across hours, days, and individuals. The temporal resolution of such behavioral recording can determine whether particular rhythms are detected and what their apparent characteristics are. A simple example is that recording only the degree of "nocturnality" of a behavior may lead to the erroneous conclusion that a rhythm has been lost when only its phase relation to the light cycle has changed.In other situations the appropriateness of particular units of analysis is more ambiguous. In a field study of monkey troops (Nilgiri langurs, Presby tis johnii), Horwich (1976) recorded hourly means of feeding and calling averaged over several days; the data obtained showed clear dawn and dusk peaks, especially of feeding. However, a finer-grained analysis of individual troops during a single day revealed previously undetected ultradian behavioral cycles. Horwich concluded that the presence of significantly different individual (or troop) patterns and day-to-day variations can be obscured by grouping data across individuals and over days in search of the population mean. But the most detailed analysis is not always the best, since excessive attention to detail and individual differences can obscure biologically significant population trends and prevent the formulation of meaningful generalizations.In order to choose among these possible descriptive strategies, it is useful first to identify some of the sources of behavioral variability among individuals and across time. If individual variability is generated as the sum of independent, stochastic determinants, then the average pattern in the population will also be the modal (i.e., most common) pattern. But if individual variability reflects the presence of naturally separate subpopulations, then the "species-typical pattern" may have little biological meaning. To take an extreme example, a bimodal activity pattern in a population might result from one subpopulation's preying on dawn-active species and another's utilizin...

Effect of weather conditions on the communal roosting behaviour of common ravens Corvus corax with unlimited food resources

“…The effect of day length suggests utilisation of the light phase during winter to a larger extent whereas the effect of cloud cover indicates that daily-activity budgets of ravens as diurnally active birds are modulated by light intensity. This is in agreement with the general view on circadian rhythms in birds, assumed to be primarily governed by photoperiod and light intensity as zeitgeber (Aschoff 1960;Daan and Aschoff 1975;Rusak 1981;Brandstätter 2002). Surprisingly, moonlight did not provide additional illumination to delay roosting times of ravens.…”

Partitioning of Time as an Ecological Resource

“…Thus, many generations of selection for diurnal activity in golden spiny mice have not caused a shift in their underlying rhythmicity. The diel rhythms that normally enable mammals to respond to environmental stimuli appropriately (e.g., Rusak 1981, Ticher et al 1995 appear to lack the plasticity required to enable A. russatus to adapt to community-level interactions, even at this evolutionary scale.…”

Time-of-day variation in the sensitization of the acoustic response in pigeons

“…The circadian clock regulates many behavioral and physiological processes (Rusak, 1981;Turek, 1985) and certain oscillatory mechanisms suggesting a rhythm in learning and memory have been reported (Tapp & Holloway, 1981;Raghavan et al, 1999;Kole et al, 2001). However, the effects of circadian modulation of learning and memory are not yet fully understood.…”