Browsing by Author "McGregor, Peter K."
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- Chorusing by male european fiddler crabs, Uca tangeri: A study of visual communication netwoksPublication . Burford, Fiona R. L.; McGregor, Peter K.; Oliveira, Rui FilipeChorusing behaviour, in which males aggregate and advertise to attract females, has been extensively studied in acoustically signalling orthopterans and anurans. Species which agregate and signal visually have comparanble behaviour but chorusing aspects has been studied infrequently. Male fiddler crabs (genus Uca) signal by waving and enlarged claw and form signalling aggregations, therefore, they have a potential to form a visual chorus. This study investigated the chorusing behaviour of male eurpoean fiddler crabs, Uca tangeri. The timing of waving by groups of three males (trios) was studied when each male was alone and when all three males were present. When waving in a trio, the male with the largest claw significantly increased the lenght of its interwave interval and some such males tend to wave soon after the other males. This pattern of waving may enhance the effectiveness of the large-claw males signal by avoiding visual object grouping and by allowing females to assess relative claw size more readily.
- Considerations on the use of video playbacks as visual stimuli: The Lisbon workshop consensusPublication . Oliveira, Rui Filipe; Rosenthal, Gil G.; Schlupp, Ingo; McGregor, Peter K.; Cuthill, Innes C.; Endler, John A.; Fleishman, Leo J.; Zeil, Jochen; Barata, Eduardo Nuno; Burford, Fiona R. L.; Gonçalves, David; Haley, Michael; Jakobsson, Sven; Jennions, Michael D.; Körner, Kay; Lindström, Leena; Peake, Thomas; Pilastro, Andrea; Pope, Denise S.; Roberts, Sam G. B.; Rowe, Candy; Smith, Jerome; Waas, Joseph R.This paper is the consensus of a workshop that critically evaluated the utility and problems of video playbacks as stimuli in studies of visual behavior. We suggest that video playback is probably suitable for studying motion, shape, texture, size, and brightness. Studying color is problematic because video systems are specifically designed for humans. Any difference in color perception must lead to a different color sensation in most animals. Another potentially problematic limitation of video images is that they lack depth cues derived from stereopsis, accommodation, and motion parallax. Nonetheless, when used appropriately, video playback allows an unprecedented range of questions in visual communication to be addressed. It is important to note that most of the potential limitations of video playback are not unique to this technique but are relevant to all studies of visual signaling in animals.
- Functions of mudballing behaviour in the european fiddler crab Uca tangeriPublication . Oliveira, Rui Filipe; McGregor, Peter K.; Burford, Fiona R. L.; Custódio, Maria do Rosário Viegas dos Santos; Latruffe, ClaireEuropean fiddler crabs place mudballs around their burrow openings. Both males and females placed mudballs, but there were major differences between the sexes in mudballing behaviour, suggesting that the female’s mudballs were a by-product of digging out the burrow whereas the male’s may have additional functions. When the male’s mudballs were removed experimentally, the number and intensity of male–male agonistic interactions increased significantly. Experimentally visually isolated males spent longer making mudballs and less time waving. In a binary choice test, females were more likely to approach dummy males with mudballs, spent longer near these males and were more likely to enter their burrows than dummy males without mudballs. The same pattern was apparent for males with 30 rather than 20 mudballs. These results are consistent with a dual function for mudballs in U. tangeri: to reduce the number and intensity of aggressive interactions between neighbouring males and to attract females.
- Human exploitation of male fiddler crab claws: Behavioural consequences and implications for conservationPublication . Oliveira, Rui Filipe; Machado, José Luis Gorjão H. C.; Jordão, Joana; Burford, Fiona R. L.; Latruffe, Claire; McGregor, Peter K.Male fiddler crabs have one of their feeding claws greatly enlarged, which may comprise up to 40% of their weight. In southern Portugal (Ria Formosa) the major claw of the fiddler crab Uca tangeri is a local delicacy. Fishermen break off the male major claw and throw the crab back into the mudflat to regenerate a new one. Approximately 38 % of the males sampled had a missing or a regenerating claw. Although individuals are not removed from the population the operational sex ratio is biased towards females since other males and females behave towards clawless males as if they were females. Moreover, removing the major claw from males prevents them from signalling (waving display) to females to attract them to their breeding burrows and it also places them at a disadvantage if they have to defend their burrows from males with intact claws. Thus, the harvesting of male fiddler crab claws has potential consequences at the population level. In this paper we investigated these potential consequences by comparing an exploited population of fiddler crabs at Ria Formosa with a remote population at the Mira estuary that is not under human exploitation. The unexploited population has significantly larger males and a significantly higher density of burrows. The operational sex ratio is also significantly different between the two populations with a female-biased sex ratio in the exploited population. These preliminary results suggest that claw harvesting in fiddler crabs has a measurable effect at the population level. The consequences of this type of fishery in which the individuals are not removed from the population but the population structure is potentially affected need further investigation.
- Intersexual differences in the mudballs of Uca annulipes (Decapoda: Ocypodidae)Publication . Burford, Fiona R. L.; McGregor, Peter K.; Oliveira, Rui FilipeThis study investigated the features of mudballs produced by male and female Uca annulipes. Both sexes formed mudballs from mud excavated from within the burrow during the final hour of the low tide period. Males placed the centre of the mudball aggregation and the furthest mudball significantly further from the burrow than females. These observations suggest that the placement of male mudballs was not simply a by-product of burrow excavation.
- Male-like mudballing behavior of some female fiddler crabs (Uca tangeri)Publication . Burford, Fiona R. L.; McGregor, Peter K.; Oliveira, Rui FilipeAt each low tide, male and female Uca tangeri remove mudballs from inside their burrows and place them on the surface. Previous studies have shown clear intersexual differences in mudball arrangements. However, we noticed that some females placed their mudballs in an arrangement similar to that of males. In this study, we investigated several factors that may have been responsible for this change in female mudballing behavior. We found no significant effect of the lunar cycle, female size and reproductive state, or burrow features. We briefly discuss the avoidance of sexual coercion or parasite modification of host behavior as possible factors. Our study shows that intersexual differences in mudballing behavior are more complex than previously thought.
- Mudballing revisited: Further investigations into the construction behaviour of male Uca tangeriPublication . Burford, Fiona R. L.; McGregor, Peter K.; Oliveira, Rui FilipeMale and female Uca tangeri (the only ddler crab species to inhabit Europe) construct mudballs from mud excavated from within their burrows. Individual males placed similar patterns of mudballs each low tide, suggesting that there is some degree of stereotypy. When mudballs were experimentally moved further from the burrow or closer to it, males only repositioned those that were moved closer, placing them further away again. However, males did not replace mudballs that had been experimentally destroyed at the end of the mudballing phase when they had started to court females. In binary presentation tests, females showed no signi cant differences in response to mudballs made from different types of mud, or different numbers of mudballs. These results are consistent with earlier ndings that male mudballs function as territory boundaries. However, we provide evidence that male mudballs have no function in female attraction, contrasting with previous studies.
- The sequence of mudball placement by male fiddler crabs, Uca tangeriPublication . Burford, Fiona R. L.; McGregor, Peter K.; Oliveira, Rui FilipeMale Uca tangeri place mudballs in the area surrounding their burrows each low tide to delineate territory boundaries. We investigated the sequence of mudball placement by noting the distance at which each mudball was placed and its location in one of eight sectors around the burrow. Ten of the 13 focal males placed their mudballs in a pattern that was significantly different from random. No relationship was found between mudball distance from burrow and order of placement in the mudball sequence. However, most males placed each mudball in the same or a nearby sector to that of the previous mudball.
- Then and now: a brief history of acta ethologicaPublication . McGregor, Peter K.; Oliveira, Rui FilipeInexistente
- Video playback techniques in behavioural researchPublication . Oliveira, Rui Filipe; McGregor, Peter K.; Schlupp, Ingo; Rosenthal, Gil G.Inexistente