Activity patterns of insectivorous bats and birds in northern Scandinavia (69° N), during continuous midsummer daylight

Speakman, J.R., Rydell, J., Webb, P.I., Hayes, J.P., Hays, G.C., Hulbert, I.A.R. and McDevitt, R.M. 2000, Activity patterns of insectivorous bats and birds in northern Scandinavia (69° N), during continuous midsummer daylight, Oikos, vol. 88, no. 1, pp. 75-86.

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Title Activity patterns of insectivorous bats and birds in northern Scandinavia (69° N), during continuous midsummer daylight
Author(s) Speakman, J.R.
Rydell, J.
Webb, P.I.
Hayes, J.P.
Hays, G.C.
Hulbert, I.A.R.
McDevitt, R.M.
Journal name Oikos
Volume number 88
Issue number 1
Start page 75
End page 86
Total pages 12
Publisher Wiley
Place of publication London, England
Publication date 2000-01
ISSN 0030-1299
1600-0706
Summary Previous studies suggest that many species of insectivorous bats are nocturnal, despite the relatively low availability of their insect prey at night, because of the risk of predation by diurnal predatory birds. We hypothesised that if this was the case bats living above the arctic circle would alter their feeding behaviour during midsummer because there would no longer be any benefit to restricting their activity to the period when their prey are least abundant. Alternatively, if bats were more influenced by competition from aerial insectivorous birds they would continue to feed at ‘night’ to avoid such competition. In northern Norway (69° N), during continuous midsummer daylight, insectivorous sand martins (Riparia riparia) concentrated their aerial feeding activity when aerial insects were most abundant. The birds stopped feeding between 23:00 and 07:00 when aerial insects were least abundant. In contrast, northern bats (Eptesicus nilssonii), fed mostly between 22:00 and 02:00, coinciding with the lowest aerial insect availability, and with the period when light levels were lowest (ca 1000 lux). Bat activity patterns were closest to those predicted by the avian competition hypothesis. The low densities of both sand martins and Northern bats in the study area, however, were less consistent with this hypothesis. Possibly populations of both species were higher historically and the observed patterns reflected historical competition. Bat activity was most closely correlated to ambient light levels. This raised two alternative explanations that we could not eliminate. Perhaps there was differential predation risk, between the brightest and darkest parts of the day, because the visual capacities of falcons are strongly dependent on luminance. Alternatively the bats may have been entrained to emerge at given light levels by their behaviour at other times of year.
Language eng
Field of Research 069999 Biological Sciences not elsewhere classified
Socio Economic Objective 970106 Expanding Knowledge in the Biological Sciences
HERDC Research category C1.1 Refereed article in a scholarly journal
Copyright notice ©2000, Wiley
Persistent URL http://hdl.handle.net/10536/DRO/DU:30058264

Document type: Journal Article
Collection: School of Life and Environmental Sciences
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