Bat Biology - Energetics Research Group

Chiropteran nocturnality

Almost all bats are completely nocturnal. This is remarkable given the enormous numbers of chiropteran species (around 1000) and the fact they have such diverse feeding behaviour – ranging from species that are exclusively frugivorous and feed mostly by vision and smell, to bats that are carnivores and insectivores feeding exclusively by echolocation.

The reasons why most bats are nocturnal is confusing because if they extended their activity patterns into the daytime they would have available to them a wealth of resources that are otherwise closed to them. The consequences of this restriction of their activity to the night may in part constrain their reproductive performance. For example, small aerial insectivorous bats in the temperate zone normally give birth to only a single young each year, while small aerial insectivorous birds that occupy effectively the same niche as bats but in daylight manage to raise broods of 4 to 6 offspring and may do this two or even three times during the temperate summer.

  • pdfs for most of these publications are available for free download here.

Because expanding their activity into daylight would bring enormous advantages in terms of access to resources the presumption is made that there must be some factor that constrains their activity into the nocturnal niche.

Three hypotheses have been advanced. First, bats may face direct competitionand be out-competed by aerial insectivorous birds. Second, bats that fly in daylight may be susceptible to predation by diurnal predatory birds. Third, bats may be susceptible to uptake of solar radiation across their wing membranes which might lead daylight flying bats into fatal hyperthermia.

My first explorations in this field were via a survey of occurrences of daytime flying in bats in the UK. This survey ran during 1988 and 1989 and generated 420 reports of bats flying in daylight. The survey revealed that in 3.1% of these cases (n = 13) the bats were attacked by a predator and on 5/13 cases the interaction ended fatally for the bat. I estimated from these reports that a bat flying in daylight in the UK would have a 99% probability of being predated if it flew in daylight for only 64h! This seemed to support the predation hypothesis but a potential problem with these data was that there might be a big bias in the reports sent in to the survey towards spectacular events like interactions with predators. What was really needed was an experimental release of bats in daylight.

During the 1989 International Bat Research Conference I met up with a bat researcher from Australia called Lindy Lumsden who was engaged in a large scale ringing programme. As a matter of course in the work at that time bats were being ringed and released in the daytime. We arranged that Lindy would record the behaviour of bats she was releasing. The results backed up the UK data. In fact bats flying in daylight in Australia were even more likely to be predated by birds than those in the UK.

We followed up this work by making an expedition to the Azores archipelago in the mid-atlantic. The Azores provide a natural experiment to test these ideas because they are an environment that is free of avian predators but they contain an endemic bat species – the Azorean bat (Nyctalus azoreum). Peter Webb and I visited the islands for 2 weeks in the summer of 1992 and recorded the activity of the bats in the day and at night. Although the islands are predator free they are also free of aerial insectivorous birds and so separating between the hypotheses would not be possible. However, if either the competition or predation ideas were correct we might expect the Azorean bats to fly in daylight much more frequently than continental species of bats.

Before we made the expedition I went to the British Museum of Natural History to see what the bat we were going to find looked like. The bats in the Museum had been collected (with a shot gun by the look of them) in the 1890s by the Hon. W Rothschild. Interestingly most of the labels had comments on them like that in the picture “Flying above pinewood in bright sunshine 4.30 pm”!!!

The Azores consists of the remains of a series of extinct (and not so extinct volcanos) the caldieras of which contain lakes. Within only about 5 hours of arriving on the islands we saw our first day time flying bat from the rim of one of these extinct craters.

Our work showed that Azorean bats are still predominantly nocturnal in their behaviour, but they have an enormous amount of daylight flying activity relative to populations in areas where there are predators and competitors. The work confirmed the idea that ncturnality is subject to some selective pressure that keeps bats constrained in the nocturnal niche.

To separate whether this pressure is predation or competition we organised a much more ambitious expedition a few years later toNorthern Norway. The aim here was to study populations of the Northern bat (Eptesicus nilsonii) that lives near Tromso above the Arctic circle. The expedition members were myself, Jens Rydell from Lund in Sweden who had worked extensively on E nilsonii in Sweden, Peter Webb, Jack Hayes, Graeme Hays, Ian Hulbert and Regina McDevitt.

Northern Norway in mid-summer is neither a predator nor a competitor free environment. However it is a nocturnal free environment. For a period of a few weeks the sun doesn’t set and so the bats living there face a problem – They have no night in which to hide from predators or competitors.


SPEAKMAN, J.R. (1990)
The function of daylight flying in British bats.
Journal of Zoology 220: 101-113.

SPEAKMAN, J.R. (1991)
The impact of predation by birds on bat populations in the British Isles.
Mammal Review 21 Iss 3: 123-142.

SPEAKMAN, J.R. (1991)
Why do insectivorous bats in Britain not fly in daylight more frequently?
Functional Ecology 5 Iss 4: 518-524.
This paper was featured on the front cover of the issue.

SPEAKMAN, J.R., Lumsden, L.F. and Hays, G.C. (1994)
Predation rates on bats released to fly during daylight in south-easternAustralia.
Journal of Zoology 233: 318-321.

SPEAKMAN, J.R. and Webb, P.I. (1993)
Taxonomy, status and distribution of the Azorean bat (Nyctalus-azoreum).
Journal of Zoology 231: 27-38.

SPEAKMAN, J.R. and Hays, G.C. (1992)
Albedo and transmittance of short-wave-radiation for bat wings.
Journal of Thermal Biology 17 Iss 6: 317-321.

SPEAKMAN, J.R. (1995)
Chiropteran nocturnality.
Symposium of the Zoological Society of London 67: 187-201.

SPEAKMAN, J.R., Hays, G.C. and Webb, P.I. (1994)
Is hyperthermia a constraint on the diurnal activity of bats?
Journal of Theoretical Biology 171 Iss 3: 325-339.

Rydell, J. and SPEAKMAN, J.R. (1995)
Evolution of nocturnality in bats - potential competitors and predators during their early history.
Biological Journal of the Linnean Society 54 Iss 2: 183-191.
See also independent review of this paper in BBC Wildlife (May 1995)

Lancaster, W.C., Thomson, S.C. and SPEAKMAN, J.R. (1997)
Wing temperature in flying bats measured by infrared thermography.
Journal of Thermal Biology 22 Iss 2: 109-116.

Thomson, S.C., Brooke, A.P. and SPEAKMAN, J.R. (1998)
Diurnal activity in the Samoan flying fox, Pteropus samoensis.
Philosophical Transactions of the Royal Society of London Series B - Biological Sciences 353 Iss 1375: 1595-1606.
See also independent review of this paper in Nature online

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 (69ÂșN), during continuous midsummer daylight.
Oikos 88 Iss 1: 75-86.
See also independent reviews of this paper in
New Scientist (Oct 1999)
Canadian Wildlife (Dec 1999)
Toronto Globe and Mail (Dec 1999)
Nature: News and Views (March 2000)

Thomson, S.C. and SPEAKMAN, J.R. (1999)
Absorption of visible spectrum radiation by the wing membranes of living
pteropodid bats.
Journal of Comparative Physiology B - Biochemical Systemic and Environmental Physiology 169 Iss 3: 187-194.

Thomson, S.C., Brooke, A.P. and SPEAKMAN, J.R. (2002)
Soaring behaviour in the Samoan flying fox, Pteropus samoensis.
Journal of Zoology (London).256: 55-62

Clustering behaviour during emergence from roosts

SPEAKMAN, J.R., Bullock, D.J., Eales, L.A. and Racey, P.A. (1992)
A problem defining temporal pattern in animal behaviour - clustering in the emergence behaviour of bats from maternity roosts.
Animal Behaviour 43 Iss 3: 491-500.

SPEAKMAN, J.R. (1993)
Defining temporal pattern in the emergence behaviour of bats from maternity roosts: some pitfalls in analysis and how to overcome them.
Bat Research News (1993).

SPEAKMAN, J.R., Stone, R.E. and Kerslake, J.E. (1995)
Temporal patterns in the emergence behavior of pipistrelle bats, Pipistrellus-pipistrellus, from maternity colonies are consistent with an antipredator response.
Animal Behaviour 50: 1147-1156.

SPEAKMAN, J.R. and Tallach, N. (1998)
Do emerging pipistrelle bats lose control of their timing due to 'crowd pressure'?
Journal of Zoology 246: 445-448.

SPEAKMAN, J.R., Irwin, N.R., Tallach, N. and Stone, R.B. (1999)
Effect of roost size on the emergence behaviour of pipistrelle bats.
Animal Behaviour 58: 787-795.

Irwin, M.R. and SPEAKMAN, J.R. (2003)
Azorean bats cluster during emergence despite the lack of avian predators.
Acta Chiropterologica 5:185-192

Energetics of Echolocation and flight

SPEAKMAN, J.R., Anderson, M.E. and Racey, P.A. (1989)
The energy-cost of echolocation in pipistrelle bats (Pipistrellus-pipistrellus).
Journal of Comparative Physiology A - Sensory Neural and Behavioral Physiology 165 Iss 5: 679-685.

This paper was featured on the front cover of the journal

PEAKMAN, J.R. and Racey, P.A. (1991)
No cost of echolocation for bats in flight.
Nature 350 Iss 6317: 421-423.

This paper was featured on the front cover of the issue and was the subject of a 'News and Views' article in the same issue.

see also independent reviews of this paper in
BBC Wildlife magazine (June 1991)
Science News (July 1991)
The Lisbon Times (June 1991)
The European (June 1991)
this paper was also the subject of several radio and TV broadcasts
Tomorrow’s World (BBC 1, May 1991)
Radio 4 Science Now (May 1991)
BBC World Service
(syndicated worldwide: June 1991)

see also article on this work in the McGraw-Hill Yearbook of Science and Technology (1994).

SPEAKMAN, J.R. (1993)
The evolution of echolocation for predation.
Symposia of the Zoological Society of London 65: 39-63.

SPEAKMAN, J.R. (1999)

The evolution of flight and echolocation in pre-bats: an evaluation of the energetic efficiency of reach hunting.
Acta Chiropterologica 1: 3-16.

SPEAKMAN, J.R. (2001)
The evolution of flight and echolocation in bats: another leap in the dark.
Mammal Review 31 Iss 2: 111-130.


SPEAKMAN, J.R. and Racey, P.A. (1986b)
The influence of body condition on sexual development of male brown long-eared bats (Plecotus-auritus) in the wild.
Journal of Zoology (London) 210: 515-525.

SPEAKMAN, J.R. and Racey, P.A. (1987)
The energetics of pregnancy and lactation in the brown long-eared bat (Plecotus auritus). Chpt. 21 pp 367-394. In 'Recent advances in the study of bats' (Eds. Fenton, M.B., Racey, P.A. and Rayner, J.M.V.) CUP Cambridge.

Racey, P.A. and SPEAKMAN, J.R. (1987)
The energy costs of pregnancy and lactation in heterothermic bats.
Symposia of the Zoological Society of London 54: 107-125.

Racey, P.A., SPEAKMAN, J.R. and Swift, S.M. (1987)
Reproductive adaptations of heterothermic bats at the northern borders of their distributions.
South African Journal of Science 83 Iss 10: 635-638.

Hughes, P.M., SPEAKMAN, J.R., Jones, G. and Racey, P.A. (1989)
Suckling behaviour in the pipistrelle bat (Pipistrellus-pipistrellus).
Journal of Zoology 219: 665-670.

Webb, P.I., SPEAKMAN, J.R. and Racey, P.A. (1992)
Inter individual and intraindividual variation in wing loading and body-mass in female pipistrelle bats - theoretical implications for flight performance.
Journal of Zoology 228: 669-673.

Webb, P.I., SPEAKMAN, J.R. and Racey, P.A. (1992)
Oxygen-consumption and evaporation during parturition in a vespertilionid bat (Pipistrellus-pipistrellus).
Journal of Reproduction and Fertility 94 Iss 2: 525-528.

McLean, J.A. and SPEAKMAN, J.R. (1996)
Suckling behaviour in the brown long-eared bat (Plecotus auritus).
Journal of Zoology 239: 411-416.

McLean, J.A. and SPEAKMAN, J.R. (1997)
Non-nutritional maternal support in the brown long-eared bat.
Animal Behaviour 54: 1193-1204.

Entwistle, A.C., Racey, P.A. and SPEAKMAN, J.R. (1998)
The reproductive cycle and determination of sexual maturity in male brown long-eared bats, Plecotus auritus (Chiroptera: Vespertilionidae).
Journal of Zoology 244: 63-70.

McLean, J.A. and SPEAKMAN, J.R. (1999)
Energy budgets of lactating and non-reproductive brown long-eared bats (Plecotusauritus) suggest females use compensation in lactation.
Functional Ecology 13 Iss 3: 360-372.

McLean, J.A. and SPEAKMAN, J.R. (2000)
Morphological changes during postnatal growth and reproduction in the brown long-eared bat Plecotus auritus: implications for wing loading and predicted flight performance.
Journal of Natural History 34 Iss 5: 773-791.

McLean, J.A. and SPEAKMAN, J.R. (2000)
Effects of body mass and reproduction on the basal metabolic rate of brown long-eared bats (Plecotus auritus).
Physiological and Biochemical Zoology 73 Iss 1: 112-121.

Korine, C., SPEAKMAN, J.R. & Arad, Z. (2004)
Reproductive energetics of captive and free-ranging Egyptian fruit bats (Rousettus aegyptiacus)
Ecology 85: 220-230

SPEAKMAN, J.R. and Thomas, D.M. (2003)
Physiological ecology and energetics of bats. Pp 430-492. In Kunz, T.H. and Fenton, M.B. (Eds). ‘Bat Biology’. University of Chicago Press Chicago, USA


SPEAKMAN, J.R. (1988)
Position of the pinnae and thermoregulatory status in brown long-eared bats (Plecotus-auritus). Journal of Thermal Biology 13 Iss 1: 25-29.

SPEAKMAN, J.R. and Racey, P.A. (1989)
Hibernal ecology of the pipistrelle bat – energy-expenditure, water requirements and mass loss, implications for survival and the function of winter emergence flights.
Journal of Animal Ecology 58 Iss 3: 797-813.
See also independent review of this paper in BBC Wildlife (March 1989)

SPEAKMAN, J.R., Webb, P.I. and Racey, P.A. (1991)
Effects of disturbance on the energy-expenditure of hibernating bats.
Journal of Applied Ecology 28 Iss 3: 1087-1104.
see also independent reviews of this paper in
British Wildlife (July 1991)
The Economist (February 1993)
this paper was featured on the Canadian Science program "Quirks and Quarks", broadcast across the US and Canada, Nov 1993.

Hays, G.C., Webb, P.I. and SPEAKMAN, J.R. (1992)
Arrhythmic breathing in torpid pipistrelle bats, Pipistrellus-pipistrellus).
Respiration Physiology 85 Iss 2: 185-192.

Hays, G.C., SPEAKMAN, J.R. and Webb, P.I (1992)
Why do brown long-eared bats (Plecotus-auritus) fly in winter?
Physiological Zoology 65: 554-567.

Webb, P.I., SPEAKMAN, J.R. and Racey, P.A. (1996)
How hot is a hibernaculum? A review of the temperatures at which bats hibernate.
Canadian Journal of Zoology - Revue Canadienne de Zoologie 74 Iss 4: 761-765.

SPEAKMAN, J.R. and Rowland, A. (1999)
Preparing for inactivity: how insectivorous bats deposit a fat store for hibernation.
Proceedings of the Nutrition Society 58 Iss 1: 123-131.

Humphries, M.M., Thomas, D.W. & SPEAKMAN, J.R. (2002)
Climate mediated energetic constraints on the distribution of hibernating bats.
Nature 418: 313-316

Humphries, M., SPEAKMAN, J.R., and Thomas, D. (2005)
Temperature, hibernation energetics, and the cave and continental distributions of little brown bats. In Functional and Ecological aspects of the biology of bats. (Ed. T.H. Kunz) Chicago
University press

Kokurewicz, T. and SPEAKMAN, J.R. (2006: in press)
Age related effects on energy metabolism during torpor in Daubenton’s bats: effectson fat accumulation prior to hibernation.
Acta Chiropterologica


SPEAKMAN, J.R., Racey, P.A., Hutson, A.M., Webb, P.I. and Burnett, A.M. (1991)
Status of Nathusius pipistrelle (Pipistrellus-nathusii) in Britain.
Journal of Zoology 225: 685-690.

SPEAKMAN, J.R., Racey, P.A., Catto, C.M.C., Webb, P.I., Swift, S.M. and Burnett, A.M.
Minimum summer population and densities of bats in N.E. Scotland near the northern borders of their distributions.
Journal of Zoology 225: 327-345.

Rydell, J., Strann, K.B. and SPEAKMAN, J.R. (1994)
First record of breeding bats above the Arctic-circle - northern bats at 68-70oN in Norway.
Journal of Zoology 233: 335-339.

Entwistle, A.C., Racey, P.A. and SPEAKMAN, J.R. (1996)
Habitat exploitation by a gleaning bat, Plecotus auritus.
Philosophical Transactions of the Royal Society of London Series B - Biological Sciences 351 Iss 1342: 921-931.

Entwistle, A.C., Racey, P.A. and SPEAKMAN, J.R. (1997)
Roost selection by the brown long-eared bat (Plecotus auritus).
Journal of Applied Ecology 34 Iss 2: 399-408.

Webb, P.I., SPEAKMAN, J.R. and Racey, P.A. (1996)
Population dynamics of a maternity colony of the pipistrelle bat (Pipistrellus pipistrellus) in north-east Scotland.
Journal of Zoology 240: 777-780.

Jenkins, E.V., Laine, T., Morgan, S.E., Cole, K.R. and SPEAKMAN, J.R. (1998)
Roost selection in the pipistrelle bat, Pipistrellus pipistrellus (Chiroptera: Vespertilionidae), in northeast Scotland.
Animal Behaviour 56: 909-917.

Entwistle, A.C., Racey, P.A. and SPEAKMAN, J.R. (2000)
Social and population structure of a gleaning bat, Plecotus auritus.
Journal of Zoology 252: 11-17.

Swanepoel, R.E., Racey, P.A., Shore, R.F. and SPEAKMAN, J.R. (1999)
Energetic effects of sublethal exposure to lindane on pipistrelle bats (Pipistrellus pipistrellus).
Environmental Pollution 104 Iss 2: 169-177.

Water loss

Hays, G.C., Webb, P.I., French, J. and SPEAKMAN, J.R. (1990)
Doppler radar - a noninvasive technique for measuring ventilation rate in resting bats.
Journal of Experimental Biology 150: 443-447.

Webb, P.I., Hays, G.C., SPEAKMAN, J.R. and Racey, P.A. (1992)
The functional-significance of ventilation frequency, and its relationship to oxygen-demand in the resting brown long-eared bat, Plecotus-auritus.
Journal of Comparative Physiology B - Biochemical Systemic and Environmental Physiology 162 Iss 2: 144-147.

Webb, P.I., SPEAKMAN, J.R. and Racey, P.A. (1993)
Defecation, apparent absorption efficiency, and the importance of water obtained in the food for water-balance in captive brown long-eared (Plecotus-auritus) and Daubentons (Myotis-daubentoni) bats.
Journal of Zoology 230: 619-628.

Webb, P.I., SPEAKMAN, J.R. and Racey, P.A. (1993)
The implication of small reductions in body-temperature for radiant and convective heat-loss in resting endothermic brown long-eared bats (Plecotus auritus).
Journal of Thermal Biology 18 Iss 3: 131-135.

Webb, P.I., SPEAKMAN, J.R. and Racey, P.A. (1994)
Postprandial urine loss and its relation to ecology in brown long-eared (Plecotus-auritus) and Daubentons (Myotis-daubentoni) bats (Chiroptera, Vespertilionidae).
Journal of Zoology 233: 165-173


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Megabats and Microbats: Bat Biology - Energetics Research Group
Bat Biology - Energetics Research Group
Megabats and Microbats
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