Behavioural biology is a major discipline within biology, centred on the key concept of `behaviour.' But how is `behaviour' defined, and how should it be defined? We outline what characteristics we believe a scientific definition should have, and why we think it important that a definition have these traits. We then examine the range of available published definitions for the word. Finding no consensus, we present survey responses from 174 members of three behaviour-focused scientific societies as to their understanding of the term. Here again, we find surprisingly widespread disagreement as to what qualifies as behaviour. Respondents contradict themselves, each other, and published definitions, indicating that they are using individually variable intuitive, rather than codified, meanings of `behaviour. ' We offer a new definition, based largely on survey responses: "Behaviour is the internally coordinated responses (actions or inactions) of whole living organisms (individuals or groups) to internal and/or external stimuli, excluding responses more easily understood as developmental changes." Finally, we discuss the usage, meanings and limitations of this definition. KeywordsBehaviour; Definition; Philosophy of Science; Levels of Organization The biological study of behaviour has grown tremendously over the last half century. Biosis Previews tags 42,286 items published in 2007 with the Concept Code "behavioral biology." Dozens of scientific societies, journals, courses, textbooks, etc. are organized around the central concept of behaviour. While behavioural biology interacts with a wide range of other disciplines, the unifying concept in behavioural biology is, as the name implies, behaviour. But while our understanding of behaviour has advanced tremendously since Tinbergen (1955) defined it as "the total movements made by the intact animal," our formal definition has failed to keep pace with this progress.What do we mean by this word, `behaviour'? There are numerous published definitions, and for many biologists the meaning is simply and clearly intuitive. However, satisfying definitions of this word, in the context of modern biology, are hard to find. Many definitions are so vague as to be impossible to apply. Others are crafted around a particular taxon such that members of other taxa by definition cannot behave (e.g. "Behavior involves the interaction between an Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public Access Author ManuscriptAnim Behav. Author manuscript; available in PMC 2010 July 1. Published in final edited form as:Anim Behav. Tinbergen...

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A population of California voles, Microtus californicus, living on Brooks Island in San Francisco Bay was studied for 13 years. During the first 2 years following its establishment, the performance of the population was significantly different from that in the subsequent 11 years. The 11—year pattern that developed is characterized by: (1) annual peaks in abundance; (2) a delay of up to 5 months between the return of wet season conditions and population growth; and (3) an alternating pattern of "high" and "low" winter densities. Reproduction shows a strongly seasonal pattern, beginning 1—2 months after the start of the rainy season and ending with the desiccation of the vegetation in June. In contrast to this, reproduction started promptly with the autumn rains during the initial 2—year colonization phase, and limited summer reproduction occurred as well. Within the breeding season, litter size and number of corpora lutea produced per ovulation episode show marked seasonal changes which appear to be independent of annual variations in demographic detail and condition of the mice. Males are more vagile than females, although both show a reduction of movements during the main breeding period. The incidence of wounding was positively correlated with reproductive condition in males, but not in females. Mortality schedules were studied by means of population age structure, recruitment rates, and sex ratios. Apparent aging ceases for almost 5 months from about 1 month after the dry season begins to 60 days after it ends. This period is associated with heavy mortality, particularly among old males and young females. Consequently, late fall and early winter sex ratios favor males. In general, however, females survive longer than males, and during the breeding season the sex ratio progressively favors females. Recruits first appear 1—2 months into the wet season, but initially their numbers are very few and are insufficient to reverse population declines. Rapid population growth in late spring is largely dependent on reproduction by these early recruits. Physiological condition was measured by study of body—weight changes, particularly ratios of body weight to body length, ectoparasite loads, including scabies mite infections (mange), and molting patterns. The body—weight data reveal that wet season condition, especially in spring, is much better than dry season. Surprisingly, males begin to recover during the winter period whereas females continue their decline. Moreover, the whole pattern of weight losses is more severe in poor survival summers than in the alternate ones. A flea—mite index reveals a strong seasonal pattern which seems to be induced by vole demography; during the colonization period, ectoparasites were barely noticeable. It took 4 years for scabies to reach significant levels of infestation. Highest incidence generally occurs in winter, and an outbreak occurred in the seventh winter; subsequently, the mange mites returned to endemic levels. Molt activity showed two strongly marked seasonal peaks, one in t...

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