BIRDING OBSERVATIONS AROUND VIADUCT FLATS, SAANICH, BRITISH COLUMBIA JUNE 1994 - MAY 1995 Michael A. Carson Victoria Natural History Society Victoria, British Columbia DRAFT COPY April 1996 TABLE OF CONTENTS Text Background ................................................ p. 1 Scope of the survey ....................................... p. 2 Monthly checklist ......................................... p. 2 Use of the area by birdlife The lake ............................................. p. 3 The adjacent shore and marsh ......................... p. 4 The eastern woods ................................... p. 5 The western woodland edges ........................... p. 5 The fields ........................................... p. 6 Comparison with other local wetlands ...................... p. 7 Viaduct Flats: The past and future ........................ p. 8 Conclusions ............................................... p. 9 References ................................................ p. 10 Acknowledgements .......................................... p. 10 Attachments Map of Viaduct Flats area Birding Checklist for Viaduct Flats area (2 pages) Table showing average number of birds seen by species per survey, by month, Viaduct Flats area, June 1993-May 1994 Graph showing lake level at Viaduct Flats, relative to arbitrary datum, April 1994 to June 1995. One metre above datum corresponds to top of bridge at outflow. Table showing probability of observation of water-based birds seen on weekly bird counts June to August at Viaduct Flats, Swan Lake and Blenkinsop Lake Appendix Viaduct Flats weekly bird count: raw data for period June 1994 to May 1995 (12 pages) BIRDING OBSERVATIONS AROUND VIADUCT FLATS by Michael A. Carson BACKGROUND Viaduct Flats has always been a popular place for Victoria birders, but its attractions have increased spectacularly in the last few years. A Great Egret visited the marsh in October 1993 and in the same autumn the water surface was almost covered with migrating waterfowl. A few months later, up to six Swamp Sparrow arrived to spend the winter there. Much of the recent attraction of the Flats for birdlife appears to have resulted from the fact that a debris dam on the outlet creek (marked as A on attached map) impounded water through the summer and fall of 1993 for the first time in several years. In most summers, the Flats have been cultivated and have then stayed dry until late-autumn rains. The availability of this wetlands habitat at Viaduct Flats during summer and autumn has become particularly important following the draining of many nearby wetlands. The low rainfall of autumn-winter 1993 provided little alternative habitat on the peninsula for migrating waterfowl which further enhanced the importance of the Flats. Subsequent monitoring of the outlet creek showed that the debris dam has taken on the appearance of a beaver dam, lined with mud. Though no definitive sighting of the beaver itself is known, stripping of bark on trees in the vicinity of the dam has become quite conspicuous. These events of 1993 convinced several people in the Society that Viaduct Flats has emerged as a special, indeed unique, wetlands habitat on the Saanich Peninsula. The abundance and diversity of waterfowl using the water in migration, including rafts of more than a dozen Ruddy Ducks, far exceeds anything observed on the only other comparable local wetlands at Swan Lake. With this perspective, the Parks and Conservation Committee thought it important to provide a 12-month inventory of the wetlands while it was still flooded on a year-round basis. At the same time, a proposal was put forward to the Horticulture Centre of the Pacific (which leases the Flats and surrounding area from BC Lands) to retain the Flats as a permanent wildlife sanctuary. The one-year once-a-week survey began in June 1994 and continued through until May 1995. The marshland remained flooded throughout the duration of the survey, and in fact remains so at the time of writing. SCOPE OF THE SURVEY The survey was not restricted to the lake and surrounding marshland. It also included the woodland on the eastern side of the Flats and the woodland edges on the western side of the marshland. In part, these areas were included because higher sites on these slopes provided additional opportunities to scope the lake and its margins. This is especially true on the eastern side, parts of which are difficult to see from the west shore. The other reason for inclusion of these adjacent areas is that it was felt that such relatively isolated terrain near to the marshland might prove attractive to some passerines that are not common in the more suburbanized parts of the peninsula. The route taken is shown on the attached map. Each survey took between 3 and 3.5 hours. Starting time ranged from 7 a.m. in summer to 9 a.m. in winter. In general, all surveys were done at the weekend under conditions that were comparable from the standpoint of bird observation. Rainy days and windy days were avoided as far as possible. All counts of waterfowl must be regarded as underestimates. Although all ducks on the open water could be seen and identified by scope, others were hidden in rushes and grasses at the water's edge. Some of these (up to 50 or more) were flushed during the course of the survey, but much of the hidden water's edge on the east side was not covered. Some species were certainly missed in the study. The only one known to us, however, is an American Bittern that was seen several times during the winter by Darren Copley. As part of tbe regular survey, water level was monitored on the bridge over the outlet creek. The fluctuations are shown in the attached time-graph. MONTHLY CHECKLIST The 1994-95 survey produced observations of 134 species, 6 more than in the 92-93 survey of the Blenkinsop Lake area, and 16 more than in the 93-94 survey of the Rithet's Bog area. The annual total is all the more impressive given that the spring of 1995 was one of excellent weather with no storms conducive to good "fall- outs" of migrants. In addition, lack of time prevented as many extra mid-week surveys during the spring as had been undertaken at Rithet's Bog and around Blenkinsop Lake. The breakdown by bird groups was as follows: water-based birds, 29 species; non-perching birds, 42 species; passerines, 63 species. It had been hoped to bolster the checklist by examination of records in prior years, as done for Blenkinsop Lake and Rithet's Bog, but time limitations prevented this work. USE OF THE AREA BY BIRDLIFE The large number of species seen during each bird survey is a reflection of the wide variety in habitats found in the northern Glendale Lands: open water, marshland margins, open and dense woodlands, forest edges, bare fields and meadows. The lake A record of the lake level was maintained through the survey and is given in the attached figure. The abrupt drop in water level in mid-August was due to destruction of the dam by unknown persons. By the time that the breach had been discovered and the dam repaired (10 to 20 hours), the water level had dropped by 10 cm. Winter water levels were much higher than in the previous year, and up to 75 cm higher than the later summer minimum. From December through to the end of the survey, in fact, levels were so high that the bridge over the outlet creek was almost submerged and access to the bridge was difficult even in gum boots. Peak water level occurred on December 26, in response to heavy rains on Christmas Day and Boxing Day, the water level being flush with the top of the bridge over the outlet creek. In the summer the number of waterfowl on the lake was not as impressive as during the rest of the year. Most had migrated north to breeding grounds on the mainland. However, the water body attracted a good number of different species, as well as encouraging several to breed. Apart from the expected Canada Goose and Mallard population, most conspicuous of these breeding waterfowl was the Pied-billed Grebe with its wonderful mating call. Six adults were frequently seen during June-July and at least three distinct families of young were produced. Young were being fed small fish; adults were occasionally noted to be consuming bull frogs. Another highlight was the successful breeding of a family of 4 young Ring-necked Ducks, only the second record for Vancouver Island. A single male was seen on the lake in the first two weeks of June, while the female and her brood appeared on July 3. A pair of Ruddy Ducks was also seen in the first three weeks of June, the female disappearing by June 19, only to reemerge with 6 ducklings on July 10. This is also an unusual breeding record for the Island. The splendid male Ruddy Duck remained on the lake until the female and young left the nest. Other dabbling ducks besides Mallards were also seen on the lake during late spring and early summer including both Blue-winged Teal and Cinnamon Teal and a hybrid of the two. Most of the time, however, these dabblers (except Mallards) were hidden in the reeds and sloughs, and were much less evident than the diving waterfowl. A family of young Cinnamon Teal appears to have been seen on only one occasion as it was flushed from the reeds by a human intruder. A family of Wood Duck also seemed to prefer the cover of the reed margins to the open water of the lake itself. Returning waterfowl were evident as early as mid-August with numbers of species peaking at 16 on November 20 (a total not reached again until May 13 1995), and total numbers peaking at a thousand on October 29. During winter, waterfowl numbers were generally substantially lower and, with water depths generally in excess of two metres, diving ducks tended to dominate. Indeed, at this time of the year, the waterfowl population was generally comparable with that at Swan Lake, the few dabbling ducks tending to be in the shallower grassy margins. Winter numbers could be very variable during the day, however, with large influxes at times from the east (presumably Elk Lake) including Canvasbacks and the occasional Redhead. Water levels in the summer of 1995 were noticeably higher than in 1994 due to continued activity of the beaver. Isolated visits in July showed the level to be 11 cm higher than at the same time in the previous year. No systematic survey was kept of waterfowl during the summer of 1995, but one visit on July 19th indicated 362 ducks (334 Mallards) including two juvenile Wood Ducks and three juvenile Ring-necked Ducks. The adjacent shore and marsh The belt of shore habitat flanking the lake was, most of the time, thin to non-existent because of the high water level. Solitary Sandpipers and both Yellowlegs species were both noted in spring 1994 wading at the north end, prior to the start of the survey, but few shorebirds were seen in spring 1995 because of the much higher water level (25 cm higher in May 1995 than twelve months earlier). A larger number of species was seen during autumn 1994, perhaps because of the slightly lower water level, but shore habitat was still scarce, to the frustration of shorebirds and birders alike. Peeps, Pectoral Sandpiper, both Yellowlegs and a Long-billed Dowitcher were seen along with Killdeer, but invariably in flight, searching the Flats for somewhere to land. Not infrequently the brown algal surface was mistaken for mud upon which a shorebird would attempt to alight before realizing at the last minute that something was strangely wrong. On the ground, shorebirds were more frequently seen in the hilltop pond in the hayfield south of the woods of the Horticulture Centre than at Viaduct Flats itself. This irrigation pond seems to attract shorebirds in much the same way as McIntyre Reservoir in the Martindale Valley, though not to the same degree, perhaps because of its steeper sides and greater distance from the coast. The broad band of surrounding marsh vegetation of rushes, cattails, sedges and grasses were dominated in early summer by Red-winged Blackbirds and a smaller number of Marsh Wrens. More exciting, however, were the occasional calls and glimpses of both Sora and Virginia Rail. At least 8 of the latter were detected in different places around the lake edge, perhaps indicating that number of nesting pairs. Up to 3 Sora were found in different sites. All margins of the lake appeared to harbour these rails, with perhaps a slight preference for the western side. Most of the rail habitat was flooded by the rise in water level during winter, but an occasional bird was seen during the winter, though not to the same extent as at Rithet's Bog in the previous year's survey. Numbers of Common Snipe were also much reduced in winter compared to autumn, possibly due to the flooding of much its preferred habitat. Movement of snipe between Viaduct Flats and Quick's Bottom was noticed on several occasions. During the winter, Marsh Wrens and sparrows (mostly Song Sparrows but occasionally Lincoln and Swamp sparrows) were the most common birds in the marsh area. Swamp Sparrows are rare on Vancouver Island, normally overwintering in the eastern United States. On the Christmas Bird Count, an American Bittern was flushed from the reeds, another rare sighting for the Saanich Peninusula. The eastern woods The eastern woods comprise dense Douglas-fir forest on the lower slopes and more open areas with some Garry Oak and Ocean Spray on the rocky hilltop. Relatively few birds and bird species were noted in the summer, but the habitat proved more attractive during the autumn migration period. Numbers remained good during the winter, especially in the open areas: ideal habitat for Northern Flicker, Rufous-sided Towhee, Song Sparrow, Fox Sparrow, Dark-eyed Junco and House Finch. A Barred Owl was seen on several occasions in the heavily wooded area during the winter. The western woodland edges A wide variety of passerines was heard or seen along the edges of the woods west of the marshland in summer. These included up to five singing Willow Flycatcher, a pair of House Wren and about six singing Swainson's Thrush, at least three Northern Orioles, as well as the more usual woodland birds. Typically Willow Flycatchers were found on the lower brushy slopes of the western hill or singing in willow bushes on the edge of the marsh. This species is rapidly declining in British Columbia because of loss of brushy habitat and nest-parasitism by cowbirds. According to Campbell and Harris (1994) the species may be extirpated in the province within a decade at present rates of decline. The use of Viaduct Flats margins by such a (relatively) large number of (presumably) breeding Willow Flycatcher is therefore a point worth emphasizing. The abundance of this species elsewhere in the Greater Victoria area is largely unknown because most birds arrive in late May after the annual spring bird count. Numbers at Viaduct Flats in future years should perhaps be monitored to document the stability of this local population. Perhaps even more exciting than the abundance of Willow Flycatcher, was the spring arrival of three colourful Northern Orioles, one adult male, one adult female, and one presumed to be a sub-adult male (yellow rather than orange), the three staying together through most of June. The three birds ranged widely over the northern Glendale Lands and a male (presumably one of these three) was reported as far away as West Saanich Road in the last week of June. Breeding of the orioles is suspected, and a nest was found in late June in a fir tree on the southwest side of the lake, but though adults were seen close to it, hatching of young was never confirmed. However, since more one than bird with "female" plumage was noted on several occasions near the male, some of these may have been juveniles. A pair of orioles, possibly the same pair, began nesting in the same tree in June 1995. Northern Orioles have nested in this general area (Viaduct Flats-Quick's Bottom-West Saanich Road) in most years since 1980. Only one or two other records of this species are available each year in the Greater Victoria area. The fields The wildflower meadow (an overgrown bulb field) south of the lake attracted the expected species: American Goldfinch and Pine Siskins feeding on thistles in late summer; Savannah Sparrows and Lincoln Sparrows in the fall. The largely bare bulbfield that slopes down to the western side of the lake was less heavily utilized by birds. American Pipits were seen once in fall migration. During most of the winter, the field was largely devoid of birds, though its margins were frequented by ground-feeding sparrows at all times of the year. Birds of prey Raptors were not as commonly seen here as in the previous surveys at Blenkinsop Valley and Rithet's Bog. A pair of Red-tailed Hawks nested in the adjacent woods and were resident most of the year, presumably attracted by the availability of Eastern Cottontail as a food supply. Northern Harrier was seen only once, hunting low over the marsh during the autumn. Accipiters were not frequently seen around the lake, though both common species were often noted further south around Glendale Lodge. The only falcon seen during the course of the year was an immature Peregrine Falcon spectacularly stalking a Green-winged Teal on the frozen lake surface. The infrequent sighting of falcons was a marked contrast to both the Blenkinsop and Rithet's Bog surveys. Presumably this is due to the deeper water at Viaduct Flats and the dominance of diving waterfowl rather than dabblers. Falcons seem to prefer shallowly-flood fields where dabblers are not only "sitting ducks" but also available in much larger quantity. No special owl surveys were undertaken but a Northern Sawhet-Owl was found dead near the marsh during the fall migration, Great Horned Owls responded to calls on the Christmas Bird Count, and, as already noted, a Barred Owl was occasionally seen in the eastern woods. COMPARISON WITH OTHER LOCAL WETLANDS Viaduct Flats is unique on the Saanich Peninsula. The flooded area is about 20 acres in extent and appears to be less than 1 metre deep in most places in summer and early fall, though no detailed bathmetric survey is available. The only areas even approximately comparable in terms of habitat are the "Narrows" between Elk and Beaver lakes to the north east of Viaduct Flats, Blenkinsop Lake, and Swan Lake Nature Sanctuary further into the heart of suburbia. None of these other areas has the diversity and abundance of water-based birds on a year-round basis as Viaduct Flats. The Narrows area is larger (about 60 acres) and somewhat deeper (up to 3 metres) than the Viaduct Flats wetlands. The water body margins are heavily wooded, and shore area vegetation is typically waterlily rather than the grass, rush and sedge of Viaduct Flats. The only waterbird species noted as breeding in the Narrows area during 1992 were Canada Goose, Wood Duck, Mallard and Hooded Merganser (Summers and Sterling, 1993). Up to 7 other species of waterfowl were noted for the Elk-Beaver Lake complex at other times of the year by the Summers-Sterling report, but not all of these appear to have used the Narrows area. Blenkinsop Lake is in some ways a smaller version of the The Narrows, being dominated by waterlilies in the summer, a thin fringe of cattails and woodland margins, and of comparable depth. A summary of the 1992 summer (breeding) inventory for water-based birds is given for comparison with Viaduct Flats and Swan Lake in the attached table. The Swan Lake area comprises about 23 acres of lake surrounded by another 45 acres of reeds and rushes. The lake is substantially deeper than the water at Viaduct Flats (averaging about 2.5m in depth with a maximum of 6m in winter) and is therefore less attractive to dabblers than to diving ducks. A three-year record for water-based birds is given in the table, based on weekly observations on the regular Nature Centre birding walks during 1992-94. No breeding records have been found but the observational table seems to indicate that breeding is confined to Mallards and Canada Goose. Other local wetland areas, such as Rithet's Bog and Quick's Bottom are virtually overgrown with grasses, rushes and similar vegetation, and provide very limited waterfowl habitat on a year round basis. Other lowland areas such as Martindale Flats, Hastings Flats etc. are flooded in the winter only (Carson, 1994b). VIADUCT FLATS: THE PAST AND FUTURE In previous years, without a dam on the outlet creek, the Flats have been essentially winter-flooded fields, farmed for potatoes in summer as the low area has dried out. In that period, birding was primarily focussed on winter waterfowl and spring shorebirds. Taylor (1990, p.54) describes it as follows: "Dabbling ducks are well-represented with Northern Shoveler, Ring-necked Duck, Eurasian Wigeon and migrant Blue-winged and Cinnamon Teal. As the fields begin to dry in May, they harbour migrating shorebirds. Semipalmated Plover, Lesser and Greater Yellowlegs, Pectoral Sandpipers, Western and Least Sandpipers and both Dowitchers. Spotted Sandpipers nest along the ditches." The new all-year lake has modified this bird regime somehat. As previously noted, waterfowl are dominant in autumn rather than winter. The higher water levels in winter and spring now restrict dabblers to the reed areas while the open water is dominated by diving species. In addition, the high spring water level leaves little exposed area for shorebirds, and some of the few noted in this study were seen around the reservoir in the field to the southeast of the Flats rather than around the lake itself. The new hydrologic regime has thus created a new bird regime. The major contribution of the beaver dam has been the creation of a staging area for waterfowl during autumn migration: a major asset given the scarcity of suitable habitat elsewhere on the Saanich Peninsula at that time of year. It would be useful, however, if water levels could be controlled by a weir on the outlet creek. This would allow drawdown to expose shorebird habitat in the spring, as well as additional drawdown in the winter time to provide for a more balanced mix of dabbling and diving waterbirds. The possibility of such a weir, as part of a management plan to protect the wetlands as wildlife habitat, has been discussed with BC Lands, the Horticulture Centre of the Pacific and Ducks Unlimited, but at this time no firm committment has been established from all the relevant parties. On the contrary, there is also discussion about making the area a Saanich Municipal Park, presumably much like Rithet's Bog. In the event that the land is taken over by Saanich, it can only be hoped that trails are kept well away from the lake. Increased usage of the trail around Rithet's Bog has produced significant disturbance of birdlife there, with several incidents of mauling of waterfowl and herons by dogs being reported. Hopefully a better fate awaits the birdlife of Viaduct Flats. CONCLUSIONS At a time when scarce wetland habitat is being continually lost through drainage and changes in landuse, it is unusual to come across the creation of new wetland habitat. The lake at Viaduct Flats, created by a beaver dam, has become a splendid addition to the wetlands habitat of Greater Victoria. It affords good-to- excellent birding throughout the year, a breeding area for waterfowl species that only rarely breed on southern Vancouver Island, and, above all, a major staging area for waterfowl during the southward autumn migration at a time when most similar shallow bodies of water on the Peninsula have dried up. It is hoped that the authorities responsible for the management of Viaduct Flats will recognize this and take steps to preserve the wetland habitat of this area and the margins around it which act, so importantly, as a buffer from the rest of suburbia. REFERENCES Campbell, R.W. and M. Harris, 1994. British Columbia nest records scheme: 36th and 37th annual reports (1991 & 1992). The BC Naturalist, v. 33 (3) (May/June), 4-7. Carson, M.A., 1994a. Birding observations around Blenkinsop Lake. The Victoria Naturalist, 50 (4), 4-11. Carson, M.A., 1994b. Overwintering habitats of Trumpeter Swans in the Victoria area. The Victoria Naturalist, 51(2), p. 8-21. Carson, M.A., 1995. Birding observations around Rithet's Bog. The Victoria Naturalist, 51(3), p. 8-17. Summers, K. and T. Sterling, 1993. Study of the impact of recreational use on the waterfowl species and their habitats on Elk and Beaver lakes. Report by KS Biological Services to CRD Parks Department. Taylor, Keith, 1990. A Birder's Guide to Vancouver Island. ACKNOWLEDGEMENTS The surveys described here were in almost all cases undertaken by two of us. Assisting on a regular basis were Tom Gillespie, Gordon Hart and Ellen Tremblay. Also helping out on occasion were David Allinson, Jerry Anderson, Dannie Carsen, Aziza Cooper, Claudia and Darren Copley, Mike McGrenere and Graham Ruxton. Data for Swan Lake were kindly provided by staff of the Swan Lake Nature Sanctuary based on the regular twice-weekly surveys.