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. ENDIX essiner une carte au ~e") ,L ] j " I "it Gl1.eo-t Btu, Hwm ."", :;:.i &f,ac"-CJwwntd N,(ght H"", )/ ,_,.,,11;, Voubt'-cJl.eUtd COllmo"",," ! Gulli I j r,ta.nd flooded 601tMt FOllut 011 .ote.e.p .6.tope Veep OOl1.eAt Too many vti-UD1L6 fol1.MtI1.y opeJl1Ltio.. Vea.th DO ;(;Jr.'eA wW~aU Replacement by anothell. .6peuu ans. ~aJt.6 . JIV HIM A/Y A THREE YEAR STUDY O? THE GREAT BLUE HERON IN SOUTHWESTERN BRITISH COLUMBIA John P. Kelsall and Keith Simpson canadian Wildlife Service P.O. Box 340, Delta British Columbia, Canada since 1977 we have been studying various aspects of the status and vi- apility of colonies of the great blue heron, A~dea herodiaa, en the south- western mainland of British Columbia. Much.of our data remain .to be ana- lyzed, statistically and biologically. This is an interim'report which will cover some of the highlights of the research. While some of our re- sults reinforce those of others, we believe some of them to be original. METHODS j 1 1 R J. 1 We have studied 12 heron colonies, most of them through 3 breeding seasons. We have actual counts or estimates of the number of successful nests in each colony in each year, and fledgling success per nest per col- ony has been determined in 27 of 33 cases. Comparing our results with those in the literature, notably Mark (1976), leads us to believe that the study area nesting habitat, comprising large groves of large t~ees near heron feeding habitat, has been much eroded by urban and industriai sprawl and development. Consequently there are fewer colonies than recorded in the past. However, there is compensation in that the overall size of indi- vidual colonies is larger and the total population of herons appears to be at least as great as in the past. Thus a colony at the University of Brit- ish Columbia, that was thought to be much depressed in 1972 with only '22 active nests. had 118 nests in 1978. Small colonies on both sides of the Canada-United States border at Point Roberts (longitude 123025' N. latitude 490 W), have repeatedly had to relocate because of urban development since 1945. They are now temporarily safe just inside the United States with 240 active nests in a single colony, by far the most that have ever been recorded. The high count of nests at a colony in Vancouver's Stanley park, that has been under public scrutiny since 1921, was 42 nests in 1978 des- pite intensive and growing use of the general nesting area for human recre- ation. During tne 3 years 1977 to 1979 we have had from 650 to 800 repro- ductively successful nests under surveillance. RESULTS and DISCUSSION I Ii , tl i Nestina Trees. Within each colony we found remarkable fidelity to the choice of a single tree species for nesting, even in mixed forest when other suitable tree species are readily available. However, the species of choice varies between colonies. Four colonies, which contained half our birds when first enumerated, were in red alder (Alnus rubra). An additional 4 colonies, which contained 72 ,nests in total, were situated in Douglas Fir (Pseudotsuga menziesii), and 4 with 158 nests in total were in black cot- tonwood (Populus triahoaarpa). One colony of 10 nests was found in Sitka spruce (Piaea sitahensis). In 2 colonies a mixture of trees were used, perhaps through necessity. A 54 nest colony north of Vancouver made use of -69- Proc. Colonial waterbird Group, 1979. Vol. 3, 69-74.