Showing papers by "Carel ten Cate published in 2002"

Birdsong and male—male competition: Causes and consequences of vocal variability in the collared dove (Streptopelia decaocto)

Abstract: Summary Bird songs are assumed to have a dual function: attracting mates and deterring rivals. Hence, they are likely to be subject to sexual selection. Most studies on signal evolution through sexual selection concentrate on the first function: mate attraction. In this chapter we concentrated on vocal signals involved in male-male competition, and, in particular, territorial defense. Broadcasting species or individual identity and territory ownership are usually considered to be the main functions of territorial signals. Far less is known about whether such signals may also act as assessment signals, providing honest information about the sender's competitive abilities. On theoretical grounds, such a function is to be expected. We review the evidence that interindividual variation in vocal characteristics may provide a message about male competitive ability. This evidence is fragmentary. Some vocal parameters may be suitable indicators of differences in such abilities, but few studies demonstrate that they are actually used in this way. As a case study on this issue, we examined the role of vocal variation in the territorial “perch-coo” vocalization of the collared dove ( Streptopelia decaocto ). The perch-coo consists of three elements that are produced in series. Heavier males show a higher proportion of perch-coo elements with a “modulation,” a sudden increase in frequency at the start of an element. They also show fewer coos in which the third element is lacking. The available evidence about how doves vocalize suggests that production of both modulated elements and three-element coos require greater strength or respiratory capacity. Playback experiments show that coos with modulated elements give rise to stronger responses from territorial males, that is, they are perceived as originating from a stronger competitor. The strongest responses are given to modulations with a magnitude close to the population average. Presence or absence of the third element only leads to different responses when combined with reduced length of the coo. These results show that at least part of the interindividual variation in acoustic parameters of the perch-coo conveys meaningful information about sender quality to receivers. This demonstrates the potential for intrasexual selection as a factor shaping territorial signals. The findings highlight the point that the study of signal variation in a competitive context is a neglected but fruitful area for research. The challenge for future studies will be to link vocal variation to specific modes of vocal production and to relate it to more specific aspects of “sender quality.” This will help us to understand the relationship between signal content and signal design and may shed light upon the role of birdsong as a multicomponent signal.

Diverge or merge? The effect of sympatric occurrence on the territorial vocalizations of the vinaceous dove Streptopelia vinacea and the ring-necked dove S. capicola

Abstract: Sympatric occurrence of two closely related species is expected to lead to diverging or converging shifts in signal characteristics of one or both species. We examined signal characteristics in the vinaceous dove Streptopelia vinacea and the ring-necked dove S. capicola, two sister species that are mainly allopatric but occur in sympatry in northwestern Uganda. Vocal characteristics of the birds in sympatry were compared with those of an adjacent and a distant allopatric population of each species. The sympatric population showed intermediate values between the allopatric populations from Uganda. However, within each species there is little geographic variation between distant allopatric populations. Since vocal differences between dove species have a genetic base, the convergence in vocal characteristics is most likely explained by hybridization. Probably, the two species came into secondary contact relatively recently. Climatic changes during the last several thousand years and recent habitat changes caused by the growing human population, may have allowed Streptopelia capicola to extend its range in the northern direction.

Vocal signals, isolation and hybridization in the vinaceous dove (Streptopelia vinacea) and the ring-necked dove (S. capicola)

Abstract: Two closely related dove species, Streptopelia vinacea and S. capicola, show clear interspecific divergence in one acoustic signal (perch-coo), but much less so in another (bow-coo). Both signals play a role in territorial defense and mate attraction and may thus convey information used for species recognition. In Uganda, there is a small zone of overlap where the two species most probably hybridize. With playback experiments in allopatric populations of each species we tested the potential of the two signal types for species isolation. Allopatric populations showed a stronger response to conspecific than to heterospecific perch-coos, but an equal response to bow-coos of either species. However, S. vinacea responded relatively stronger to S. capicola perch-coos than vice versa. The hybrid population showed an equal response to bow-coos of either species, but a marginally stronger response to perch-coos of S. capicola compared to perch-coos of S. vinacea. Hybrids have a variable and intermediate vocal structure compared to both parental species, which allowed for testing of behavioral coupling between production and perception of these signals. Hybrids showed no relationship between their coo structure and that of the species to which they respond most strongly, indicating a lack of behavioral coupling. Although perch-coos may differ sufficiently to allow species isolation, the similarity in bow-coos may allow interspecific interactions. We suggest that the similarity in bow-coos and the higher salience of S. capicola perch-coos may have allowed S. capicola to extend its range into that of S. vinacea, resulting in hybridization.

Posing as Professor: Laterality in Posing Orientation for Portraits of Scientists

Abstract: Posing orientation on portraits generally, but not always, shows a left-cheek bias. Different posing orientations may convey different messages, due to lateralization in facial expression of emotions. Right-cheeked posing orientation is expected to dominate on portraits aimed at communicating rationality. This study examines (1) the posing orientation on portraits of university professors, and (2) the impact of orientation on how ‘scientific’ viewers judged these professors to be. Older portraits show a clear right-cheek bias. Later portraits show a left-cheek bias, which may be related to their less formal nature. Normal and mirror-reversed portraits by two 18th century painters were perceived as equally scientific. However, right-cheeked originals were perceived as more scientific than left-cheeked ones. The findings support the hypothesis that biases in portrait orientation are affected by facial asymmetry in communicating different emotions.

Female responses to male coos in the collared dove streptopelia decaocto

Abstract: Birdsong is one of the main models in sexual selection studies. Most investigations focused on oscines in which male song and female preference learning occur. Yet, some non-oscines are well suited for such studies as well. In Columbidae song learning does not occur. However, like in oscines, song is involved in inter- and intra-sexual interactions. Surprisingly, experimental evidence of female song-based preferences are still largely lacking in this group. We conducted playback tests on wild-caught Streptopelia decaocto females. We tested for the sexual function of song by playing decaocto songs versus songs of an unrelated species. We then investigated female responses to trill. Although they do not produce this trait, males react more strongly to artificially trilled decaocto songs, i.e. to conspecific songs in which a trill from a S. roseogrisea song has been inserted, than to normal decaocto songs. We also tested female responses to S. roseogrisea songs. Females flew more often and with a shorter latency during decaocto songs than during wren songs, suggesting that species recognition occurred, but we found no evidence of preference for trilled decaocto songs. The low activity observed during the experiment might have obscured actual preferences. Nevertheless, females consistently reacted more to normal decaocto songs than to trilled decaocto or roseogrisea songs. This contrasts with the strong responses for trilled decaocto songs and the virtual lack of reaction to S. roseogrisea songs observed in males. Thus, female collared doves, as receivers, may have different characteristics from males and impose constraints on the evolution of song.