Variability in the temporal structure of the song has been investigated for the Australian bushcricket Requena verticalis (Listroscelidinae: Tettigoniinae: Orthoptera). Chirp interval and chirp duration of an individual male vary between two days. Males differ in their readiness to call. Sporadic singers sing consistently only in the presence of another calling conspecific or when acoustically stimulated, while steady singers call readily under acoustic isolation. Sporadic as well as steady singers change their chirp interval in the presence of another calling conspecific. Steady and sporadic singers are able to differentiate between 16 and 28 kHz, the two main frequency components of the song. There is evidence that the effect of the natural song on the temporal pattern of the call may be due to the 28 kHz frequency component. Individual variation in the temporal parameters is within 0.1 s, and the changes caused by acoustic stimulation are of similar magnitude. Further studies are necessary to evaluate if males and/or females uses these differences to discriminate between conspecifics.
Barn owls of the subspecies Tyto alba guttata which had been bred in captivity, and which had experience with prey, were examined for preferences in prey size (weight) under experimental conditions. They were offered a choice of larger and smaller prey of three weight classes (3/10 g; 10/40 g; 40/160 g) either active or inactive (laboratory mice, Mus musculus; laboratory rats, Rattus norvegicus). The frequency of choices of smaller prey increased significantly from the lowest to the highest weight class, and from inactive to active prey. Most frequently, the owls selected prey of 10 g and 40 g. It was shown that both prey size and activity had an equal influence on the decisions. Predictions were made as to which particular prey size a barn owl was going to choose. With increasing prey weight, the frequency of interrupted prey catching acts and conflict behaviour (mantling, feather ruffling) towards the prey, increased. The upper weight for acceptable active rats was about 80 g. One male, which had to supply his female and nestlings with food, subdued somewhat larger prey. Although relative profitability (net nutritive value/unit of time), calculated from the duration of handling prey, decreased with increasing prey weight, the barn owls chose the larger prey under certain conditions. I discuss a strategy which compromises time and energy costs with the search and subduction of the item.
To assess the functions of song in male house wrens (Troglodytes aedon), we examined the pattern of song output during different stages of the breeding cycle and behaviour patterns of focal males and conspecifics that were associated with song. We recorded 2093.5 bouts of song from 11 different males in 12 breeding cycles during 3 years. Most song sung prior to pairing is sung at a high volume and is given spontaneously (i.e. is apparently not produced in response to the behaviour of any conspecific). Production of high volume spontaneous song ceased immediately for at least 7 days when the male paired, but resumed immediately upon loss of the mate. Paired males sang high volume spontaneous song after mates began incubating, and almost always sang this song within 10 m of an unoccupied nest site. Several males attracted second mates to these nest sites and immediately ceased their output of high volume spontaneous song. These observations strongly suggest that high volume spontaneous song functions in mate attraction. Male house wrens do not appear to use song on a routine basis to communicate with neighbours or other males. However, they do appear to direct song at other males when territories are threatened. Song is sung at intruders in the territory and at neighbours just establishing a territory of their own. Most song sung after pairing appears to be directed towards mates. We suspect than males use song to inform mates that there is no immediate threat of predation, allowing mates to move quickly to and from nest sites. We discuss the role and benefits of descriptive, correlative studies in assessing song function.
Rudolf Frans Verheyen
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This study had two aims. First, we looked at individual differences in song characteristics between males of the European starling, and we related song behaviour to factors such as male age, pairing date, polygyny and male breeding success. Second, we experimentally tested whether song has an effect on female mating decisions. 1. During the breeding season, male starlings sing a very long and complex song consisting of a rapid succession of large number of different song types. We observed marked differences between males in average song bout length (a song bout was defined as a period of at least five seconds of song containing no pauses larger than 1.5 seconds) and in song repertoire size. Average song bout lengths ranged from 16 to 35 seconds. The individual repertoire size ranged from 23 to 67 song types. Repertoire size and average song bout length were positively correlated. 2. Both in the field and in captivity, yearling males sang shorter average song bout lengths and had smaller repertoire sizes than older males. 3. Males singing longer average song bouts and having larger repertoire sizes attracted females for pairing before their rivals with shorter average song bouts and smaller repertoire sizes.
Litter gender composition (LGC) of 33 litters of outbred Swiss albino mice was manipulated at birth to obtain 100%-male litters (MM), 50%-male litters (MF) and 100%-female litters (FF). Litter size was 10 in all cases. Litter defence by their respective dams (5-min exposure to an unfamiliar adult male) was scored on postpartum day 7. The influence of litter gender composition on the female's litter defence was tested, with identical procedure, under conditions of restricted feeding. In this case, dams were fed from postpartum days 1-7 with 80% of their normal daily requirement. Under both ad lib. and restricted feeding body weight of mothers and their litters was assessed daily. Under ad lib. feeding, dams rearing MM litters showed higher scores of Total Attacking Time than both MF and FF dams and higher frequency of Attacks and Tail Rattling episodes than MF dams. Food-restricted females showed a sharp decline in body weight and their litters a slower gain in weight than control animals. LGC did not affect mother and litter weight changes in both conditions but MM females tended to cannibalize more pups on days 6-7 than MF and FF females. Food-restricted MM and MF dams showed, respectively, lower Total Attacking Time and higher number of Attacks and Tail Rattling episodes than their own Control groups. These results show that, under ad lib. feeding, LGC affects significantly female mouse litter defence. Some possible underlying mechanisms are discussed. These results support only partly the TRIVERS-WILLARD'S hypothesis (1973) about sex-biased investment in the offspring since, even though mouse dams under ad lib. feeding defended more vigorously all-male litters, as predicted by the model, among food-restricted animals no clear shift toward a prevalent defence of female-skewed litters appeared.
The agonistic behaviour of the freshwater prawn, Macrobrachium rosenbergii, was studied in the laboratory. One hour long contests were conducted between prawns matched to size in each of the three sexually mature male morphotypes of this species; Small Males, Orange Clawed males and Blue Clawed males. An agonistic ethogram was established, consisting of 18 different acts. These acts were classified into indicators of dominance or subordinance following the application of cluster analysis. Prawns contests consisted usually of 3 phases: pre-escalated fighting phase, escalated fighting phase and post-escalated fighting phase. Contest phases differed both in the frequency of several acts and in the distribution of acts between the eventual winner and loser. In addition, the relative orientation and elevation of the opponents changed across phases. The inter and intra-individual sequences of acts of the winner and loser during the escalated fight were studied. Despite the similarity found in the behaviour of the two opponents during the escalated fighting, the eventual winner could be predicted by the relative number and duration of nips or by the relative number of times in which Complete and Incomplete-Lifting (two major displays of fight) were performed simultaneously with the snapping of the claws. Differences found among morphotypes pointed out a tendency of shifting from interactions with physical contact towards ritualized interactions without physical contact. This was correlated with the morphotypic developmental pathway and the concomitant increase of claw size.
The NEWTSEX model simulates the behavioural transition between two parts of newt courtship, Retreat Display and Creep, and models the interaction between four causal factors: the behaviour of the female, the male's spermatophore supply, his need for oxygen, and feedback from the male's own behaviour. The model predicts that, if feedback from the female is witheld at a critical point (Tail-touch), the male will revert from Creep to Retreat Display after an interval, the duration of which is proportional to his spermatophore supply. The results of an experiment in which the female's behaviour was controlled support this prediction, but a high level of variance in the results suggests that respiratory constraints on male courtship behaviour require further investigation.
Sophie Semenoff Tian-Chanski
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We studied the processes involved in the reorganization of individual behavioural profiles when the foragers were repeatedly removed on a weekly basis. Neither the age nor the hierarchical rank of the individual directly determined the development of its behavioural profile towards that of a forager profile after removal of the former foragers. However, the closeness of the relationship with the brood seems to have been decisive in the adopting of a new task by the individual. We suggest a model for the functioning of the Polistes society and its organizational genesis which involves two levels of regulation acting simultaneously. The dominance hierarchy results in a primary differentiation of behavioural states among the various members of the society. Each individual reacts preferentially according to its own behavioural state to specific categories of environmental stimulations. The type of action which it exerts on the environment both determines its momentary specialization in a specific task and modifies the stimulating situation, which then has lesser effects on the other individuals in the colony. These two processes act in parallel on all the individuals and contribute to maintaining a society with a stable, self-regulated organization. Task organization in the group can therefore be said to be a distributed function which does not require the presence of an individual central organizer.