761 number of particles remain involved in this process com- pared with the numbers that are originally captured by sus- pension feeders or trapped on the substratum. However, spiralling of these few particles is extensive. Acknowledgements We thank Goran Englund for his help in the analysis of data and for valuable discussion. Two anonymous review- ers made useful suggestions that led to improvement of the manuscript. Benke, A.C., and Parsons, K.A. 1990. Modelling black fly production dynamics in blackwater streams. Freshwater BioI. 24: 167-180. Chandler, D.C. 1937. Fate of lake plankton in streams. Ecol. Monagr. 7: 445-479. Cushing, C.E., Minshall, G.W., and Newbold, l.D. 1993. Transport dynamics of fine particulate organic matter in 2 Idaho streams. Limnol. Oceanogr. 38: 1101-1115. D'Angelo, 0.1., and Webster, 1.R. 1991. Phosphorus retention in streams draining pine and hardwood catchments in the southern Appalachian Mountains. Freshwater BioI. 26: 335-345. D'Angelo, 0.1., Webster, l.R., and Benfield, E.F. 1991. Mechanisms of stream phosphorus retention-an experimental study. 1. N. Am. Benthol. Soc. 10: 225-237. Ehrman, T.P., and Lamberti, G.A. 1992. Hydraulic and particulate matter retention in a 3rd-order Indiana stream. 1. N. Am. Benthol. Soc. 11: 341-349. Kullberg, A. 1988. The case, mouthparts, silk and silk formation of Rheotanytarsus muscicola Kieffer (Chironomidae: Tany- tarsini). Aquat. Insects, 10: 249-255. Maciolek. 1.A .. and Tunzi, M.G. 1968. Microseston dynamics in a simple Sierra Nevada lake-stream system. Ecology, 49: 60-75. Maltchik, L.. Molla, S., Casado, c., and Montes, C. 1994. Measurement of nutrient spiralling in a Mediterranean stream- comparison of 2 extreme hydrological periods. Arch. Hydrobiol. 130: 215-227. Meyer, 1.L. 1990. A blackwater perspective on riverine eco- systems. BioScience, 40: 643 - 65 I. Morin, A.. Back, C., Chalifour, A., Boisvert, 1., and Peters, R.H. 1988. Effect of blackfly ingestion and assimilation on seston transport in a Quebec lake outlet. Can. 1. Fish. Aquat. Sci. 45: 705-714. Mulholland, P.1., Newbold, 1.0., Elwood, 1.W., and Hom, C.L. 1983. The effect of grazing intensity on phosphorus spiralling in autotrophic streams. Oecologia, 58: 358-366. Mulholland, P.l., Steinman, A.D., Marzolf, E.R., Hart, D.R., and DeAngelis, D.L. 1994. Effect of periphyton biomass on hydraulic characteristics and nutrient cycling in streams. Oecologia, 98: 40-47. Newbold, 1.D., Elwood, 1.W., O'Neill, R.V., and Van Winkle, W. 1981. Measuring nutrient spiralling in streams. Can. 1. Fish. Aquat. Sci. 38: 860-863. Newbold, 1.0., O'Neill, R.V .. Elwood, 1.W., and Van Winkle, W. 1982a. Nutrient spiralling in streams: implications for nutrient limitation and invertebrate activity. Am. Nat. 120: 628-652. Newbold, 1.D., Mulholland, P.l., Elwood. I.W., and O'Neill, R.V. 1982b. Organic carbon spiralling in stream ecosystems. Oikos, 38: 266-272. Richardson, 1.S., and Mackay, R.l. 1991. Lake outlets and the distribution of filter feeders: an assessment of hypotheses. Oikos, 62: 370-380. Wallace, I.B., and Merritt. R.W. 1980. Filter-feeding ecology of aquatic insects. Annu. Rev. Entomol. 25: 103-132. Wallace, 1.B., Webster. 1.R.. and Woodall, W.R. 1977. The role of filter feeders in flowing waters. Arch. Hydrobiol. 79: 506-532. Webster, 1.R., Covich. A.P .. Tank. 1.L.. and Crockett, T.V. 1994. Retention of coarse organic particles in streams in the southern Appalachian Mountains. J. N. Am. Benthol. Soc. 13: 140-150. Wotton. R.S. 1992. Feeding by blackfly larvae (Diptera: Simu- liidae) forming dense aggregations at lake outlets. Freshwater BioI. 27: 139-149. Wotton, R.S .. Malmqvist. B.. and Ashelford, K. 1995. The retention of particles intercepted by a dense aggregation of lake-outlet suspension feeders. Hydrobiologia, 306: 125 -129. How hot is a hibernaculum? A review of the temperatures at which bats hibernate Peter I. Webb, John R. Speakman, and Paul A. Racey Abstract: We review records of the temperature at which bats (Chiroptera) have been found torpid within hibernacula in the wild. Temperatures ranged from -10 to 21°C, with a mode of 6°C for Vespertilionidae (n = 29 species) and 11°C for Rhinolophidae (n = 5 species). Both the mean minimum temperature and the mean median temperature at which species were found were significantly higher for rhinolophids (6.26 and 1O.05°C, respectively) than for vespertilionids (-0.17 and 5.68°C, respectively). Received luly 19, 1995. Accepted October 25, 1995. P.I. Webb,) J.R. Speakman, and P.A. Racey. Department of Zoology, University of Aberdeen, Aberdeen AB9 2TN, United Kingdom. ) Present address: Department of Zoology, University of Otago, P.O. Box 56, Dunedin, New Zealand (e-mail: peter.webb@stonebow.otago.ac.nz). Can. J. Zoo!. 74: 761-765 (1996). Printed in Canada! Imprime au Canada