Vision in echolocating bats - Fladdermus.net

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1979b) and three species of Phyllostomidae (Desmodus rotundus, Carollia perspicillata, and Artibeus jamaicensis, Hope & Bhatnagar 1979b) by measuring the luminance of light stimuli required to provoke electroretinogram responses. Among the vespertilionids, Eptesicus fuscus showed the highest light tolerance, and among the phyllostomids, which generally responded to lower luminance levels than the vespertilionids, Artibeus jamaicensis showed the highest tolerance. This presumably reflects the relative importance of vision in the different species, but perhaps more importantly the time at which these species normally emerge in the evening, and to what extent they are exposed to bright light (Hope & Bhatnagar 1979a; b). The Emballonuridae Emballonura spp. and Saccopteryx spp., some of which roost at exposed sites and often fly in daylight (Lekagul & McNeely 1977; Bradbury & Vehrencamp 1976; Kalko 1995), would thus be expected to be more light tolerant than other bats. Although, light tolerance levels have not been measured in these bats directly, the small receptive fields and the low receptor-to-ganglion ratio (ca 1:10) in Saccopteryx spp., compared to that of other microchiropteran species (ca 1:100), indicate a high light tolerance and good resolving power as expected. In fact they resemble diurnal mammals in this respect (Chase 1972). Nevertheless, the eyes of Microchiroptera work well under low ambient illumination, although the sensitivity to different light levels and the ability of brightness discrimination vary considerably between the different families and species. Spatial resolution The eyes of microchiropterans are primarily adapted to function in low light levels. This carries the disadvantage of a relative poor ability to resolve fine spatial details (acuity). The ability of spatial resolution of the bat eye can be estimated either anatomically, by calculating the density of retinal ganglion cells (Marks 1980; Pettigrew et al. 1998; Heffner et al. 2001) or behaviourally, by presenting the bats with striped patterns of different fineness (Suthers 1966; Bell & Fenton 1986; Paper IV). When the visual acuity is measured with the latter method, it is often referred to as grating acuity and is expressed as degrees of arc or as cycles per degree, where one cycle is one pair of black and white stripes. The two methods give indications of the minimum separable angles, i.e. the minimum distance between two points that an animal needs in order to separate them. 19
The device used for the optomotor response tests (Paper IV), in which a bat is presented with rotating, striped patterns of different fineness. The bat responds to the revolving patterns by moving its head in a stereotype manner. The thickness of the stripes corresponds to the bats visual resolving power (acuity), measured as degrees of arc. Comparisons between the two methods should be treated carefully because the acuity values estimated by counting retinal ganglion cells tend to be higher than those estimated from behavioural studies. This suggests that the anatomical method gives a theoretical minimum, rather than an indication of what the bats actually respond to. Nevertheless, Table 2 should give an idea of the wide range of spatial resolution ability that has been documented in different species of microchiropteran bats, from the coarse vision of the small Myotis spp. (Vespertilionidae) (3-5º arc, Paper IV) to the relatively fine visual ability of Macrotus californicus (Phyllostomidae) (0.06° arc, Bell & Fenton 1986). Macrotus californicus has by far the best resolving power found in any microchiropteran bat studied so far, and is comparable to that of a dog in this respect (Heffner & Heffner 1992). It is also the only microchiropteran known to be capable of detecting insects, using vision alone (Bell 1985). 20
Page 1 and 2: Vision in echolocating bats Johan E
Page 3: A doctoral thesis at a university i
Page 6 and 7: to be precedence of vision over son
Page 8 and 9: och för att undvika hinder på vä
Page 11 and 12: B ats (Order: Chiroptera) are among
Page 13 and 14: VISION IN ECHOLOCATING BATS The mic
Page 15 and 16: The microchiropteran eyes are shape
Page 17 and 18: structures, and the dorsal lateral
Page 19: 10 lux, which is equivalent to the
Page 23 and 24: Tab 2 - cont Light Visual Species (
Page 25 and 26: jamaicensis, Desmodus rotundus and
Page 27 and 28: (Davis & Barbour 1965) or when they
Page 29 and 30: Insectivores and carnivores For bat
Page 31 and 32: Moreover, the eyes of Macrotus cali
Page 33 and 34: combined with broadband echolocatio
Page 35 and 36: Multimodality - vision and echoloca
Page 37 and 38: superior colliculus. It has been sh
Page 39 and 40: Acknowledgements First of all I wou
Page 41 and 42: Buchler, E. R. & Wasilewski, P. J.
Page 43 and 44: Heffner, R. S. 1997. Comparative st
Page 45 and 46: Masterson, F. A. & Ellins, S. R. 19
Page 47: Suthers, R. A. & Chase, J. 1966. Vi
Page 51 and 52: Animal Behaviour - In Press Use of
Page 53 and 54: the ability of brown long eared bat
Page 55 and 56: General observations RESULTS When r
Page 57 and 58: are influenced to some extent by th
Page 59 and 60: Eklöf, J., Tranefors, T. & Vazquez
Page 61 and 62: Table 1. - The number of feeding at
Page 63: “The Eocene brought mammals mean
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Submitted manuscript Vision complem
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(dorsal) side up and the other had
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(Anderson et al. 1998). Hence, the
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Figure 1. - Frequency of attacks by
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Manuscript Visual acuity and eye si
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computer screen. The bats were rele
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study. On overcast nights the amoun
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Koay, G., Kearns, D., Heffner, H. E
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Tab. 1. - Eye diameter and optomoto
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“The bat that flits at close of E
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