Martin P. Gammell

David's score: a more appropriate dominance ranking method than Clutton-Brock et al.'s index

here are many procedures, of varying complexity, forranking the members of a social group in a domi-nance hierarchy (reviewed by de Vries 1998; also Jamesonet al. 1999; de Vries & Appleby 2000; Albers & de Vries2001). Roughly, two types of method can be distin-guished, one in which the dominance matrix is reorgan-ized such that some numerical criterion, calculated forthe matrix as a whole, is minimized or maximized, andone that aims to provide a suitable measure of individualoverall success, from which a rank order can be directlyderived. Two relatively simple, and somewhat similar,ranking methods belonging to the latter type are Clutton-Brock et al.’s index (Clutton-Brock et al. 1979, 1982) andDavid’s score (David 1987, 1988). Both methods can beused to calculate dominance ranks for individuals in agroup, based on the outcomes of their agonistic inter-actions with other group members, while taking therelative strengths of their opponents into account.Clutton-Brock et al.’s index (CBI) was originally devel-oped as a measure of fighting success for red deer,

Animal Contests: Analysis of animal contest data

Summary In this chapter we outline and discuss statistical approaches to the analysis of contest data, with an emphasis on testing key predictions and assumptions of the theoretical models described in Chapters 2 and 3. We use examples from an array of animal taxa, including cnidarians, arthropods and chordates, to illustrate these approaches and also the commonality of many key aspects of contest interactions despite the differing life histories and morphologies (including weaponry) of these organisms. We first deal with the analysis of contest outcomes, a useful approach for determining which traits contribute to an individuals resource holding potential (RHP). Here we outline alternative statistical approaches that treat the outcome as either an explanatory (independent) variable or as the response (dependent) variable. In both cases, we treat a single contest as one ‘experimental unit’ and consider ways in which multiple measures taken from the same experimental unit should be accounted for in the analysis. Thus, we introduce paired and repeated measures approaches for contest data and also the calculation of composite measures. We then discuss more complex mixed models, which are particularly useful for dealing with multi-party contests when multiple individuals from the same group occur in more than one observation. Having established what factors influence RHP, one might then ask questions about the roles of information-gathering and decision-making during contests. These questions are prompted by the theoretical models of dyadic contests discussed in Chapters 1 and 2, and we consider the advantages and limitations of using analysis of contest duration to distinguish between ‘mutual-’ and ‘self-assessment’ type contests. An additional tool that we can use to address this question is the analysis of escalation and de-escalation patterns, and we thus shift the focus to within-contest behavioural changes.

A winner effect supports third-party intervention behaviour during fallow deer, Dama dama, fights

Male ungulates engage in intense competition for access to females during the breeding season. Although fights are generally dyadic level encounters, they are on occasion disrupted by the intervention of third-party males. We investigated these third-party interventions using predictions derived from Dugatkins model (Dugatkin 1998, Proceedings of the Royal Society of London, Series B , 265, 433–437) of intervention behaviour. The model argues that when an individual successfully defeats an opponent there is an increase in the probability of winning a subsequent contest: a winner effect. Third-party intervention behaviour is predicted to occur as it serves to prevent either member of a competing dyad from successfully defeating his opponent, achieving a winner effect and subsequently becoming a threat to the intervener. Consistent with model predictions, our results show that intervening males held significantly higher rank than males that did not intervene and were also more likely to be dominant to both of the competing males. Intervening males did not selectively target competitors based on rank, nor did they target males based on overall dyadic rates of aggression between the intervener and competing males. Furthermore, interveners were more likely to have won their interaction immediately prior to intervention and were also likely to win their interaction subsequent to intervention when compared with contest success of the two competing males. Our results are consistent with predictions that support a winner effect for intervention behaviour in fallow deer fights.

Contest duration: sizing up the opposition?

Over 2000 years ago, Sun Tzu advised military strategists to know their own strengths and weaknesses as well as those of their enemies. Similarly, animals engaging in pairwise contests are often thought to employ mutual assessment as a means of conflict resolution, with contests being resolved more quickly the more the strengths and weaknesses of the rivals differ. In an important new paper, Taylor and Elwood argue that available evidence could be misleading and that many contests might in fact be resolved by self-assessment alone.

Investment in fighting in relation to body condition, age and dominance rank in the male fallow deer, Dama dama

According to life history theory, males of iteroparous species are expected to trade off investment between current and future reproduction based on age (mating strategy or terminal investment hypotheses) or body condition (individual quality hypothesis). However, although central to this latter model, the question concerning whether and to what extent condition regulates competitive investment in polygynous species is unknown. Consequently, we investigated this issue with reference to fight structure in fallow deer contests. Support for the individual quality hypothesis was limited: males with larger necks as determined by prerut neck girth fought for longer than males with smaller necks. However, prime-aged males had higher investment in fighting than preprime- or postprime-aged males indicating that investment in fighting might be age related. Other aspects of our results also failed to support condition-related predictions; although we found that jump clashing and vocal rate were related to weight loss and decline in neck girth, respectively, there was no relationship between investment in fighting and prerut measures of body size. Moreover, we also found that rank was predicted by investment in fighting (backward pushing) rather than body condition. Our results show that, in addition to body condition and age, variation in competitive investment between individuals also influences reproductive effort in the fallow deer.

Power rangers: no improvement in the statistical power of analyses published in Animal Behaviour

Statistical hypothesis testing is widely employed to assess the probability (P) of an effect size estimated from the observed data occurring by sampling error alone, assuming the null hypothesis (H0) is true and the alternative hypothesis (H1) is false (Popper 1968; Peters 1991; Ford 2000). The effect size is a measure of biological importance: it is an estimate of the true magnitude of an effect in the population being studied (e.g. a mean difference or a correlation coefficient) and may or may not be statistically significant (Thomas & Juanes 1996; Nakagawa & Cuthill 2007). In testing the statistical significance of an effect size, the researcher sets a significance threshold, or Type 1 error rate (a), to minimize the likelihood that a true H0 will be rejected. As a is lowered, for instance from 0.05 to 0.01, the probability of rejecting a true H0 is decreased but the probability of accepting a false H0, termed Type 2 error, is increased. If a researcher reports a nonsignificant (NS) test result, this may therefore (1) correctly identify a lack of relationship or (2) reflect a failure of the test employed to detect a real relationship, that is, a Type 2 error. Categorizations of statistical outcomes are summarized in Table 1 and we refer the reader to Nakagawa & Cuthill (2007) andMorrison (2007) for recent critiques of the ‘null hypothesis significance testing’ approach to data analysis. Allied to Type 2 error is the concept of statistical power, defined as ‘the longrun probability of detecting a given effect with our sample(s) if it actually occurs in the population(s)’ (Quinn & Keough 2002, pages 164e172; see also Cohen 1988; Rossi 1990). A simple mathematical representation is:

Is the parallel walk between competing male fallow deer, Dama dama, a lateral display of individual quality?

During competitive encounters protagonists are expected to use signals of individual quality particularly if there is a risk of injury or death. Lateral presentation of body profile, by which information regarding phenotypic characteristics associated with individual quality are displayed, may represent such a strategy. During aggressive interactions, male fallow deer frequently engage in parallel walking which is assumed to represent a mutual display of quality, as mediated by exposure of the maximal profile of the body or antlers. We examined the context and role of the parallel walk during competitive encounters to investigate whether there was evidence that dyads of competing males were assessing differences in phenotypic characteristics. There was no evidence to support the hypotheses that the parallel walk is a lateral display of body size or weaponry or that its use is associated with a reduced level of escalated or risky behaviours during fighting. Total time spent fighting was not shorter when a parallel walk was present than when there was no parallel walk. The parallel walk was highly associated with fighting and it was more likely to be initiated by the subsequent loser. Furthermore, parallel walking frequently followed bouts of fighting and as such may represent a strategy that permits an animal the opportunity to decide whether to continue fighting. Parallel walking was also associated with a failure to resolve contests in favour of one animal indicating that it may be a means of withdrawing from further fighting without incurring a loss in dominance status. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.

Third-party intervention behaviour during fallow deer fights: the role of dominance, age, fighting and body size

Third-party interventions of dyadic contests are often explained by appealing to high-level cognitive processes such as coalition formation between group members. However, alternative accounts that do not appeal to sophisticated cognitive processes have been proposed. We tested predictions from two such models using the fallow deer, Dama dama, as the model taxon: (1) a random target model that argues that intervention is directed randomly towards a target and (2) a specific target model that assumes that targeting is directed at contestants that have low resource-holding potential. Contrary to predictions of the specific target model, we found no evidence that targeting following third-party intervention increased as the resource-holding potential of the target declined. Both models argue that intervention serves to prevent individuals from gaining a winner effect and advancing up the hierarchy. Being targeted did not result in a decline in dominance rank, although targeting was associated with investment in dominance-related fighting tactics. Fight intervention was associated with an increase in rank early in the rut and accounted for increased mating success. Therefore, interveners benefited beyond simply preventing rivals from advancing in the hierarchy. In theoretical terms, a random target as opposed to a specific target model explains intervention behaviour in the fallow deer.

Win, lose or draw: a comparison of fight structure based on fight conclusion in the fallow deer

Fights between male fallow deer (Dama dama) may conclude with the contest decisively resolved in favour of one animal (the winner), or, there may be an inconclusive resolution, in which case there is no winner. We sought to compare the structure of fights between male fallow deer in order to determine what factors might be important in influencing how fights are concluded (i.e., decisively or inconclusively resolved). We compared differences in the number of backward pushes, jump clashes and retreats over fight duration; we also compared the duration of bouts of fighting. Fights that were decisively resolved had a significantly higher number of backward pushes and jump clashes than fights that were inconclusive. Decisively resolved fights also had a higher number of retreats in the final quarter of contests suggesting that, overall, fights that resulted in a winner were more costly than fights that were inconclusively resolved. There was a significantly larger asymmetry between opponents in decisively resolved fights in the proportion of backward pushes and jump clashes recorded suggesting that opponents in fights that ended inconclusively were more evenly matched. There was no difference in overall contest duration or the duration spent fighting between decisively and inconclusively resolved fights. These results indicate that the manner by which a contest concludes, is determined by the difference in action performance between contestants and also, a difference in the rate of behavioural actions as a function of time spent fighting.

The soundscape of Arctic charr spawning grounds in lotic and lentic environments: can passive acoustic monitoring be used to detect spawning activities?

Abstract The aims of this study were to (i) assess the efficacy of passive acoustic monitoring (PAM) for detecting Arctic Charr at their spawning grounds and (ii) characterize the overall acoustic soundscape of these sites. PAM was carried out over three Arctic Charr spawning grounds in the UK, one lotic and two lentic. 24-h cycles of recordings were collected prior to and during the Arctic Charr spawning season, which was determined from data returns by simultaneous net monitoring. Acoustic analysis consisted of manual quantification of sound sources, Acoustic Complexity Index (ACI) calculation and spectral analysis in 1/3 octave band (SPL; dB re 1 μPa). In the lotic spawning ground, prior to the beginning of Arctic Charr spawning, SPL and ACI showed a restricted range of variation throughout the 24-h, while during spawning the night values of SPL and ACI were found to significantly increase, concurrently with the rate of gravel noise induced by fish spawning activities and fish air passage sounds. Both prior to and during the Arctic Charr run, the lentic soundscape was characterized by diel variation due to the daytime presence of anthropogenic noise and the night-time presence of insect calls, while only a few occurrences of fish air passage sounds and gravel noise were recorded. These findings suggest that PAM over Arctic Charr spawning grounds could provide meaningful information to be used in developing management plans for this threatened species, such as determining the location and time of arrival, diel pattern and length of spawning activities.