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<br />
<br />216
<br />
<br />COLONIAL WATERBIRDS
<br />
<br />,..:..0
<br />:::;\ili
<br />more than five minutes. In addition to~i~;
<br />observations, we received reports of eag~~;
<br />heron inte,actions by local ,esidents foriWL
<br />of the 8 colonies studied. Residents neat
<br />the Powell Rive, hemn colony ,epeate<!Ii
<br />obse.ved adult eagles canying hero~'
<br />chicks towa,ds the eagle's nest. No youp"
<br />fledged from the Powell Rive, colohX:"
<br />even though eight of eleven nests observer
<br />weekly we,e known to contain chick,s;;'
<br />(B,eault, pe". obse.v.). This suggests thar'
<br />eagle p,edation is mo,e widesp,ead than::'
<br />ou, two documented cases. Eagles can al~o.
<br />cause adult herons to leave nests (Kelsall},
<br />and Simpson 1980), leaving eggs and small.
<br />young vulne,able to chilling and predation,','
<br />by co.vids. Eagles may be an importan~,;:
<br />factm affecting heron productivity.
<br />
<br />NORMAN ET J
<br />
<br />_' J hPod;m). Unpuhlished Ph.D. II
<br />'btJ . Los Angeles.
<br />~1ifornla~d R. W. Campbell. 19~7
<br />"",R. W., a . delta. populatlo
<br />." F er River. .
<br />,the ras. . ificance. Occasl
<br />'--;:internatlonal ds~gn Wildlife Servk
<br />,1<" be 65 CaDa Ian . . I
<br />IUD r }'989 The breedmg biD og~
<br />- JiR. W. .' the Great Blue H.
<br />',,", ~. tTend~ ~n ',n ,he Strait of Geo:
<br />.". ranmm, R W
<br />r I Vermeer, K. and . .
<br />- -i~mbla. n d ology of marine 31
<br />",'.. StatuS an ec B . "
<br />",- .e 5 't of Georgia, nUS
<br />l"d in the tr31 S' I Pul
<br />.9; .' 5. W'ldlife Service pecla
<br />c' adlan I
<br />~wa. S 1987. Predation on .adult
<br />-, L.. [. s it important? Colomal W
<br />erons.
<br />)(j:122. dE R Kalmbach. 19!
<br />~-'-~~R H an. F
<br />_~t~ . ". 'omic status. U. S.
<br />Iagle and Its eeon U . d State,
<br />li"f Service Circular 3D, mte. . t
<br />e W h' gton Dlstnc '
<br />'~f Interior, as In .
<br />:YSA, -' and K. Simpson. 198~.
<br />'~lId' J. r~he Great Blue Heron m
<br />'}.u yo
<br />
<br />Table 1. Observations of Bald Eagles in Great Blue Heron Colonies in 1988.
<br />
<br />Heron No. Active Observation Eagle
<br />Colony Heron Nests Time (Hours) Incursions
<br />Sidney Is., B. C. 99 270 34
<br />Crofton, B. C. 20 140 16
<br />Olympia, WA 63 16 0
<br />Tacoma, WA 49 25 0
<br />Samish Is., W A 350 80 5
<br />Nanaimo, B. C. 24 II I
<br />Powell River, B. C. 42 14 0
<br />Victoria, B. C. 64 22 0
<br />Total 712 578 56
<br />
<br />'Measured from maps (Scale 1:50,000)
<br />
<br />At the same time, an adult hemn clung
<br />from the undeJ"Side of the nest, flapping
<br />its wings and calling loudly. The eagle ,ip-
<br />ped apart and consumed at least two chicks
<br />appmximately th,ee weeks old. After
<br />th,ee minutes, the hemn let go of the nest,
<br />flew in a short ci,cle and landed opposite
<br />the eagle on the nest dm. The hewn
<br />roared and ,epeatedly lunged at the eagle
<br />but made no contact. The eagle occasion-
<br />ally lunged back at the hewn but also
<br />made no contact. The eagle departed at
<br />0610 h. A la,ge, hewn (presumed to be
<br />the male) anived at the nest at 0818 h. No
<br />live chicks we,e seen and the pair was still
<br />at the nest at 1400 h when obse,vations
<br />ceased.
<br />The second event occurred on 28 June
<br />1988 at the Samish Island colony nea,
<br />Anacortes, Washington. At 1948 h, hewns
<br />began to ma, as an adult Bald Eagle flew
<br />thmugh the colony at tree leyel. The eagle
<br />landed nea, the edge of the colony at the
<br />top of a la'ge Black Cottonwood (PoPulus
<br />trichocarpa) where five heron nests we,e lo-
<br />cated 30-40 m above the ground. The
<br />eagle seized a heron chick estimated to be
<br />fou, weeks old and canied the struggling
<br />chick away in its talons and flew towa,ds
<br />its nest, located 500 m away (Jim Watson,
<br />pers. comm.).
<br />Fo,bes (1987) ,eviewed published cases
<br />of eagle attacks on post-fledged G,eat Blue
<br />Hemns. All attacks but one took place dur-
<br />ing the fall 0, winte.. In the incursions and
<br />predation events we report, viewing condi-
<br />tions (such as distance, angle, and foliage
<br />density) made confi,mation of p,edation
<br />difficult. Acoustic detection of Bald Eagle
<br />presence was also difficult as herons stop
<br />vocalizing if eagles perch in the colony fOJ"
<br />
<br />ACKNOWLEDGMENTS
<br />
<br />Research conducted in Washington State was{:-!'
<br />funded by the U. S. Fish and Wildlife Service an~ ~he.~1_
<br />Washington State Department of Wildlife. In Bn~.sh.,.,
<br />Columbia, support was provided by the Canadian -":
<br />Wildlife Service (CWS), B. C. Forest Products, an;
<br />NSERC grant to Dr. K. M. Cheng University of.-,
<br />British Columbia (VBC) and the Anne Vallee Ecolog-
<br />ical Fund. Jim Watson, Washington StateDepartm~?t .,
<br />of Wildlife, contributed information on eagles Ifi -,-
<br />Washington. Logistical support was provided by R
<br />W. Butler, P. E. Whitehead, and K. M. Cheng. T.
<br />'Sullivan and K. Tremaine assisted in field studies
<br />while naturalists provided misceJlaneous observa-
<br />tions. R. D. Bayer, R. W. Butler, K. M. Cheng, L. S.
<br />Forbes, M. Hooper, T. E. Lacher, D. W. Mock p,
<br />Unitt, and one anonymous reviewer commented on
<br />earlier drafts.
<br />
<br />LITERATURE CITED
<br />
<br />Bayer, R. 1979. Bald Eagle-Great Blue Heron in-
<br />teractions. Murrelet 60: 31-33.
<br />Brandman, M. 1976. A quantitative analysis of the
<br />annual cycle of behavior in the Great Blue Heron
<br />
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