Torgeir S. Johnsen;
Elizabeth A. Fessler
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In mixed-sex flocks of red jungle fowl (Gallus gallus), both males and females form dominance hierarchies, and male-male aggression and female choice can influence mating success. If females prefer the dominant male, there is no conflict between intra- and intersexual selection. We studied captive flocks consisting of two males and three females. In 1998, dominant males had larger combs than subordinate males in most flocks, while in 1999, comb size did not differ between dominant and subordinate males. The dominant male crowed more and performed more wing flaps than the subordinate male, but both males performed an equal number of tidbits and waltzes. The dominant male obtained more copulations than the subordinate male. When the dominant male had the larger comb, females of all ranks preferred to mate with and associated with the dominant male. When the subordinate male had the larger comb, primary and secondary females mated with the dominant male while tertiary females mated more often with the subordinate male, and female association with a male did not predict mating. Males with large combs are preferred by females and tend to become dominant, but females seem to prefer males with large combs even when these males are subordinate.
One of the factors that may influence an animal's use of space is visibility, which in territorial species can determine how readily an individual can monitor its territory for conspecific intruders. We hypothesized that territorial red-capped cardinals (Paroaria gularis) would prefer locations that provided them with good views of their territories. Red-capped cardinals defend territories along lakes and rivers in the Amazon Basin, and visibility can vary widely within these territories. We defined visibility as the percentage of a territory that could be seen from a particular location. Visibility was measured by dividing each territory into 20 m segments and calculating the proportion of the territory that was visible from each segment. Cardinals did not distribute their time evenly within their territories: focal observations revealed that cardinals spent more time in the segments of their territory that afforded them the best view of their territory. This preference is unlikely to be due to differences in food availability, as the abundance of arthropod prey did not vary between high-visibility sites (peninsulas) and low-visibility sites (bays). Cardinals probably benefited from their disproportionate use of sites with high visibility because conspecific intruders were more likely to be detected from those sites.
Ronald L. Rutowski;
Michael J. Demlong
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We experimentally investigated proximate factors influencing the visual detection of flying conspecifics by male butterflies (Asterocampa leilia) engaged in a sit-and-wait mate-searching tactic. Model butterflies were presented to perched males in the field using an apparatus that permitted us to control the path and speed of a model while varying minimum distance of the model from the male, height of the model above the ground, and model size. The dependent variable in all cases was whether or not the male left his perch and pursued the model. Males responded to normal-size models up to but not beyond distances of 3 m, and, because doubling the model surface area increased the distance at which males responded, we conclude that males do not detect conspecifics if they are more than 3 m away. At distances of 2 m or less males perched on the ground were more likely to detect conspecifics than males perched off the ground. This is likely to be due to differences either in the background against which the perched male typically views conspecifics or how large an angle conspecifics subtend from a perched male's perspective. These results suggest that thermally-driven changes during the activity period in perch preferences have consequences for success in mate detection that may be evolutionarily significant.
It is a generally accepted concept that the secondary plant metabolites — the cyanogenic glycosides, and the pyrrolizidine alkaloids — are the main chemical compounds providing Heliconiinae, Acraeinae, Ithomiinae, the day-flaying moths Zygaenidae, and other aposematic butterflies with a potent chemical defense against their main vertebrate predators, the insectivorous birds. This author does not agree with this concept and presents a different point of view. His thesis is based on (1) the limited ability of birds to taste, (2) the inability of birds to taste via 'beak mark tasting' or simple pecking, and (3) on voluminous data and arguments in the extensive literature, dealing with many aspects of interest concerning secondary plant metabolites and their role in the chemical defense of butterflies, which do not support the generally accepted concept. In this paper are assembled the most important and convincing information opposing the view that these various chemical compounds provide butterflies with a chemical defense against bird predators. A revision of the currently accepted concept is suggested.
Luis M. Bautista;
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Current theory of risk-sensitive foraging predicts that foragers should choose feeding sites on the basis of variation in as well as mean reward rate when there is a shortfall in their food supply or a decrease in their energy budget. For a given mean reward delay, they should choose high variance feeding sites if they are running below energy requirement, but low variance sites if they are running above. It has been suggested that the smaller the animal size, the stronger the preference reversion between high and low variable feeding sites. Previous tests of the energy budget rule when there was time variability have used bird species heavier than 80 g. Hence we tested energy budget rule predictions with coal tits Parus ater, a bird of 9 g of body mass, foraging at two feeding sites with high or low variability in food delivering delay. We manipulated energy budgets by controlling air temperature in the laboratory. In one treatment (positive budget), individuals were allowed to eat at the level of their own ad-libitum daily consumption and the air temperature was set to 24°C, while for the other treatment (negative budget), temperature was set to 14°C, and food availability was limited to the maximum daily intake observed in the positive budget treatment. When air temperature was low, daily intake increased but body mass decreased. Birds were also less active in the low temperature treatment, hopping less times every day. Latency to peck decreased as well, pecking for food when it was available sooner than in the high temperature treatment. These results show that coal tits were living in a negative energy budget when air temperature was set to 14°C. Preference for the variable feeding site was greatest in the negative energy budget, as it was predicted by the energy budget rule. Contrary to the energy budget rule, coal tits consistently preferred the variable option also in the positive energy budget. Possible explanations for these results are explored, including alternative foraging models to the energy budget rule.
The territoriality of parental males and the hatching rate of egg masses in their territories were examined in Hypoptychus dybowskii, a species in which territorial males care for egg masses only just after mating, and sneaker males are known to occur. Most males deserted the territories with egg masses, but the hatching rates of abandoned and attended egg masses were similar. A large percentage of the deserted territories with egg masses were taken over by non-territorial males. Comparison of the mating success between males that deserted territories and those that attended territories showed that territory desertion occurred when males experienced fewer chances to mate. These results indicate that territorial males contributed little to embryonic survivorship after egg mass hardening, and deserted their territories depending on the mating rate. Such an unique reproductive strategy may be adaptive when there are no parental costs after arrangement of egg masses, high hatching rates of abandoned egg masses, and a high chance of sneaking.
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There is general agreement that in non-human primates, the emotional state of a caller is reflected in the vocal structure. But only few studies describe call features characterizing such correlates. This is mainly due to the fact that it is difficult to identify the emotional state of a caller. In the present study, we analysed calls from a study (Jürgens, 1979) in which squirrel monkeys had been given the opportunity to control vocalization-eliciting brain stimulation. In this way, the aversive or hedonistic quality of the emotional state underlying the production of specific calls could be determined. 758 of the recorded calls, representing 8 different call types, given by 25 subjects, were analysed in order to find out whether differences in the degree of aversion are reflected by specific acoustic parameters. It was found that an increase in aversion is parallelled, depending upon the call type, by an upward shift of maximal energy in the power spectrum, an increase in frequency range and/or an increase in the ratio of nonharmonic to harmonic energy.
Hatchlings of the Australian brush-turkey, Alectura lathami, should respond to predators innately because they hatch independently of nest-mates, have no contact with parents, and initially live solitarily. Their response to predators was tested in a large outdoor aviary set in natural rainforest habitat. Two living predators, a cat and a dog, as well as a moving rubber snake and raptor silhouette were presented to observe whether different predators evoked different innate responses. Controls consisted of cardboard boxes of equal coloration, shape and dimensions. Ten chicks were tested per stimulus type, and their response measured as latency to the first step and proportion of time spent performing different behaviours, during presentation of the stimuli and thereafter. While the snake evoked mainly running and this was obvious only during the test, the three other stimuli also led to a difference in behaviour after presentation. The raptor and cat evoked more crouching than other stimuli and the dog more running. Latency to the first step was higher in the raptor tests than during others. However, there was no difference in response between the stimuli and controls, suggesting that the releasing mechanism for evoking a response is likely to be size, dimensions, height and/or relative speed. Hatchlings were also presented with an acoustical stimulus, alarm calls of songbirds; its control was white noise. They responded to this by being more vigilant than in other tests, and, as with the snake, this response was only obvious during the test. In contrast to the optical stimuli, chicks did not respond to the control for the acoustical stimulus, indicating that megapode chicks, which have no parents to warn them, possess an innate response to alarm calls of songbirds instead. The results of this study also suggest that a lack of predator recognition should be of little concern in the translocation of endangered megapode species, even when chicks have to deal with introduced predators, and that other factors such as the availability of cover should be given greater attention.