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90 THE MURRELET TABLE 1. Prey manipulation by Great Blue Herons at Creston, British Columbia in 1981 and 1982. Size class Number Number Number Prey species (em) eaten Stabbed Mandibulated1 Black bullhead <10 5 0 0 (Ictalurus melas) 10-20 30 25 5 >20 1 1 1 Yellow perch <10 2 0 0 (Perea flavescens) 10-20 32 1 0 >20 3 I 0 Pumpkinseed <10 22 0 0 (Leponris gibboSLlS) 10-20 6 0 0 >20 0 .0 0 Largemouth bass <10 1 0 0 (Micropterus salmoides) 10-20 1 0 0 >20 1 0 0 Totals <10 30 0 0 10-20 69 25 5 >20 5 2 1 I Some fish which were Stabbed were also Mandibulated; these fish, however, were not included in the number Mandibulated. observation would appear to be consistent with Krebs' hypothesis. Mock and Mock (1980) specu- lated. that Goliath Herons killed prey by Stabbing since spine erection by spiny prey in a heron's esophagus could cause serious injury. Bowles (in Bent 1926) reported finding a dead Great Blue Heron with a large saltwater "bullhead" (Cottidae?) lodged in its throat. The "bullhead's" pectoral spines had pierced the heron's neck on both sides. Since dead Pacific staghorn sculpin and blacK bullhead relax their spines (pers. obs.) it would seem likely that Prey Stabbing in the Great Blue Heron is analogous to Stabbing in the Goliath Heron. Prey Stabbing likely was usep. with larger fish (Table 1) rather than Prey Mandibulation because either the fish were- too heavy to be Man. dibulated efficiently or the spines were too strong or both. I suggest that the reason tor Stabbing and Mandibulation at some spiny fish and not others lies in the nature of the spinal erection mechanism. 1ctalurids possess a locking mechanism to maintain erection of dorsal and pectoral spines Uordan 1907). Plainfin midshipman and Pacific staghorn sculpin, which have broad skulls, can maintain strong muscular erections of operculat and pre- opercular spines. When one of those species is aroused, the spines cannot normally be forced jnto the relaxed position without breaking (pers. obs.). Yellow perch can also maintain a strong erection of opercular spines (pers. obs.) but have narrow skulls; thus only very large perch would pose a threat to a heron, which is consistent with my observations (Table 1). Pumpkinseed (Lcpamis gib- bosus), largemouth bass (Micropterus salmoides), shiner perch, tidepool sculpin, snake prickleback and starry flounder, which possess weakly erected spines, were not Stabbed. Threespine stickleback possess locking spines (Scott and Crossman 1973) but were so small (less than 6 em) that they likely posed no threat to the heron. Nikolsky (1963) noted that spines serve to increase the eHe<:tive size ot fish and make them less available to predators, Prey Stabbing and Prey Mandibulation counter the protective adaptatj.ons of the fish and expand the range of prey available for consumption. Acknowledgemenls.-This paper is based largely on observations made during the course of a Canadian Wildlife Service study on the Great Blue Heron in British Columbia. D. R. Flook. R. W. Butler. A. M. Martel! and an anonymous reviewer eritical!y reviewed the manuscript. R. O. Bayer suggested several changes which signi.ficantly improved the manuscript K. Simpson and J. P. Kelsall provided guidance and encouragement during the course of the Pender Harbour work. I thank them all. LITERATURE CITED BENT, A. C. 1926. Life histories of North American marsh birds. U.S. NatL Mus. Bull. No. 135. JORDAN. D. S. 1907. Fishes. Henry Holt and Co., New York. KREBS, J. R. 1974. Colonial nesting and sodal feeding as strategies for exploiting food resources in the Great Blue Heron. Behaviour 51:99-131. 63(3) ---:----, I WINTER 1982 MOCK, D. C. AND K. C. MOCK. 198' 433-448. Nn<oLSKY, G. V. 1963. The ecolo~ RECHER, H. F. AND J. A. RECHER. Ecology 49:560-562. SCOTT, W. B. AND E. J. CkOSSMAN. Bull. No. 184. ,- Canadian Wildlife Service, Box 340, .i- Zoology, University of Manitoba, WiT. :: ( COLONY ES B R 5' The Great Blue Heron (ArdeQ hf can he displaced by human activit interest to note the establishment 1981, herons were seen carrying J (Thuja plicala) bordering the parI International Airport in British 0 found at the base of one of the tn nest was found later. On 24 June the tourth nest was vacant The Ir busy marinas. The nests were in a (accommodating several hundred port. A colony was active on Sea IsI; displaced by airport expansion (~ old as the trees with nests showed been selected because of its prox Fraser River foreshore and grass) found under trees with nests. It long~standing is at Point Grey, se A colony in Stanley Park. VanC! since at least 1921 (Racey 1921a, probably sufficient time for the he and Stanley Park colonies are in ( "lOllS trees and thus may buffer tn Human disturbance has displac lumhia (Mark 1974, 1976; Kelsall. as at Pitt Meadows and Crescent 1 Our knowledge, the Sea Island c< within the lower mainland. The Sea Island colony location local existence in spite of human Acknowledgemenfs.-We would commenting on the manuscript. BENT, A. C. 1926. Life histories I KELSALL, J- P. AND K SIMPSON. H British Columbia. Peoc. Co