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THE GREAT BLUE HERONS AT WALDIE ISLANDThe great blue heron is a stately wading bird magnificently adapted for its wetland existence. Few of us can say we've never seen this patient stalker that inhabits freshwater creeks, rivers, lakes, wetlands and fields. This slender large blue-gray bird is often mistaken for a crane, but in flight the heron folds its neck back over the shoulder unlike the outstretched neck of the crane. The deep harsh croaking of the heron - a "frawnk, frawnk, frawnk", which is usually uttered during takeoff, sounds reminiscent of prehistoric times. The ecologically sensitive great blue heron has public appeal as a symbol of wetland conservation.
Provincially, both the interior and coastal subspecies of the great blue heron are "blue-listed" which means they are considered vulnerable to population reduction. A more precise definition of blue-listed is: "species of concern because of characteristics that make them particularly sensitive to human activities or natural events". Only the coastal subspecies is listed "of special concern" federally, by the Committee on the Status of endangered Wildlife in Canada. The B.C. Wildlife Act (Section 34) protects herons and their nest trees from direct harm, but offers no protection for surrounding nesting and feeding habitats. The Migratory Birds Convention Act for the protection and enhancement of wildlife is an international agreement between Canada, United States and Mexico that provides additional protection for herons. Slowly wading in shallow water, the heron stands motionless for many minutes until prey comes within reach of its dagger-like bill. With lightning speed, the neck uncoils and a fish or frog is speared or caught between the mandibles. The wriggling fish or amphibian may be tossed into proper position and swallowed whole or killed by repeated stabs and then swallowed head-first. Learning to catch prey involves developing hunting skills that increase the chance of success. During the overwintering period, feeding behaviour appears to be more of a nocturnal activity; this is consistent with the vertical movements and higher densities of fish detected near the water surface at night in the vicinity of Waldie Island. In summer, the lush riparian vegetation is flooded over, providing camouflage for the hunting heron while it stalks the shallow water for prey. The diet of the great blue heron consists mostly of small fish, but herons are opportunistic and will catch small mammals (i.e. voles), amphibians (i.e. frogs), reptiles (i.e. snakes and small turtles), aquatic invertebrates, ducklings, and occasionally the young of nesting birds. Thus it is not uncommon to see a heron pursued by irate blackbirds, whose nests have been pillaged. The lumbering flight of a heron propelling itself with slow powerful strokes of wings which can span two meters, is a magnificent sight. In flight, the neck is folded backward like an "S" and the long legs trail behind. Efficient and highly vascularized "red muscles" provide the power required for sustained long flight. Herons perform marvelous acrobatic maneuvers when airborne. However, they appear awkward when approaching their precariously-positioned stick nests.
Although herons prefer a solitary existence, they get together in loose groups under certain conditions. This is the case mostly with foraging, roosting and during nesting season if prey is abundant. It is believed that colonial behaviour reduces the vulnerability of the population to predation and assists the offspring to learn potential foraging sites quickly by following the parents to various locations. Herons form monogamous pair bonds within the breeding season, but often switch mates each year. During the nesting season it is possible to differentiate between the sexes as the males develop longer plume feathers which grace their heads. Courtship behaviour is evident in late March and early April. Once pairs are bonded they are reinforced by choreographed behavioral displays which include "circle flights". These short flights start around the nest first by the male and soon the female joins him; their flight is unique as the birds fly with their necks fully extended, rather than folded back, as is normal. Copulation takes place at the nest site. Once the birds are paired, a new nest is built or an old one is refurbished. Herons are very adept at finding twigs. Usually the male brings them one at a time to the female who positions them. Although a new nest platform can be built in a few days, sometimes it may take several weeks. This can be a large investment of time and effort, so that is why nests from previous years are quickly occupied and defended. Herons may nest singly but most are colonial. Aggregations of nests in prominent trees such as black cottonwoods are known as a rookery. A rookery may be used for 35-40 years, but herons are also known to frequently change their nesting sites. A typical nesting tree appears whitewashed by accumulating guano, and the characteristic build-up of wastes and prey remnants produces a memorable aroma. The female lays 3-5 pale bluish-green eggs sometime in early to late April. Both sexes take turns sitting and turning the eggs during the 25-29 day incubation period. The chicks have a naked pink body, sparsely covered with down when they hatch. They are fed regurgitated food by the parents for up to eight weeks. Although they can fly when 60 days old, the young may stay at the nest for up to another 30 days. Towards the end of this period, the young are "weaned" by progressively scantier meals: this action finally forces them out of the nest to test out their wings. The young herons are considerably paler in appearance than the adults. Most herons reach sexual maturity in their second or third year and may live for about 18 years. The oldest banded heron known was 23 years of age. Part Two: Local Occurrence and Population Dynamics The Waldie wetland site actually consists of four functional components: Waldie Island itself, the smaller and more exposed Breakwater Island (which I so named after the remnants of the Waldie Mill breakwater crib at its upstream end), the seasonal wetland which is now traversed by boardwalks and a footbridge, and the sewage treatment facility ponds. All of these attract many species of wetland birds and make the site a prime birding area. The herons in particular use the area year-round, but they congregate there in far greater numbers in the late fall - early winter period. In 2000, BC Hydro contracted with Pandion Ecological Research (Marlene Machmer) to evaluate the behaviour and population dynamics of the local wintering heron population at this site. This preliminary study was driven by concerns about unusually high mortality numbers, with the objective being an evaluation of any possible relationship between recent river management operations and elevated heron mortality. No conclusive evidence was found of such a relationship. The study, however, did identify possible impacts on the heron population dynamics associated with the whitefish management flow regime. To maximize spawning opportunities for whitefish, BC Hydro tries to maintain a fairly constant flow rate on the Columbia River from December 21 to January 21; this is usually kept in the range of between 40,000 and 60,000 cubic feet per second. As these flows are rather low for this time of the year, the corporation is obligated to pass on compensating higher flows under the Columbia River Treaty water management agreements during the period immediately preceding the whitefish spawning phase. Historically (prior to the establishment of the whitefish window) some of the highest Keenleyside discharges have been during the early winter period in order to meet power demands south of the border. These operations coincide directly with the period when heron numbers at Waldie are the greatest. Such an accommodation for whitefish spawning needs has both positive and negative impacts on the heron population. The lower water during the whitefish phase is ideal for the wintering heron population as it opens up more foraging opportunities. The higher water during the period which precedes it tends to reduce foraging opportunities by inundating the shoreline areas and by diluting fish stocks overall. New foraging opportunities may be presented when the low-lying seasonal wetland area is flooded; however, during the winter these areas are not that productive as fish are reluctant to invade recently flooded areas and the amphibians and reptiles which make such shallow wetlands productive in the summertime are not active. Ideally, flow regimes during the heron wintering period should be adjusted so that Breakwater Island - which is the site most favoured by the wintering herons - is not totally submerged, by keeping the river level below 421 meters. The greatest consistent aggregations of the birds at this time of the year were not on the main island itself, but rather on the smaller and rather barren cobble island slightly further upstream. Unlike Waldie Island, this smaller island is exposed to the full force of the river current on one flank, and the quieter waters of the old mill pond on the other flank. Overwintering herons seem to prefer the much larger and heavily vegetated island mainly during storms and in very cold weather. In the summer, this distribution pattern is reversed: herons are often seen perched in the lodgepole pine trees which ring Waldie Island, or roosting along the more open beaches that surround the island. A further water management recommendation which arose from subsequent studies is that during the reservoir-refilling phase (spring), minimal river levels are maintained (above 418.7 meters) so that the channel between the main shoreline and Waldie Island is kept flooded. Because herons prefer the larger, vegetated island during this period, and for most of the balance of the year, any protection of the island from humans and dogs is of course critical. Herons actually attempted to establish a breeding colony on Waldie Island itself in the spring of 2001. Nests were built and several chicks were observed. This attempt failed, possibly because of human and dog activity on and near the island, and from predation pressure by bald eagles. Herons are more vulnerable to depredation by eagles and crows when nesting, and the chicks are easy targets in smaller and recently established rookeries. During the summer period, herons are also routinely harassed by ospreys, as I can relate from personal observations. Although herons generally have shown remarkable resilience and adaptability where change is inflicted on them very slowly, it must be emphasized that this observation does not apply when they are attempting to establish a new nesting territory. Herons have been known to adapt to human presence if it is not too intrusive. An example of this is a still-active large rookery in Vernon which is located in a remnant cluster of cottonwood trees surrounded by light industry. The Waldie area thus functions as a winter aggregation site for local herons which disperse to other areas in the region later in the year, where they maintain breeding sites (rookeries). It appears that the local heron population becomes concentrated at the Waldie site during this time of the year because of prevailing conditions such as an adequate foraging area and the relative absence of human disturbance. These factors are seasonal, relating to the prevailing water levels and the degree of human recreational activity and other disturbance. The highest population of herons is observed in the late autumn / early winter period when river levels are relatively high, and the availability of shallow water foraging habitat free from human interference is limited elsewhere. The overwintering population usually peaks by mid-December and a gradual decline follows, so that by mid-February, most birds are gone. A further factor which may be important could be the perceived loss of security at Waldie Island as the lowest river levels of the year render the island more vulnerable to disturbance from the mainland for a period of three months or more. The herons re-appear in modest numbers in late April and tend to congregate on Waldie Island whether or not nesting is attempted. The summer period produces new foraging opportunities as the lush herbaceous vegetation is flooded over in the Waldie wetland.
Aside from these annual migrations to breeding areas, there are also short-term rhythms imposed on the Waldie overwintering population. Usually when water levels drop significantly, the herons disperse to various foraging locations along the Columbia and Kootenay rivers to take advantage of the new feeding opportunities. These documented winter foraging locations range from Hugh Keenleyside Dam to China Creek on the Columbia (a distance of approximately 20 km.), and in the vicinity of the oxbow channel on the Kootenay. There is also a very obvious diurnal rhythm. Although overwintering herons have been observed feeding during the day, it appears that most foraging is done at widespread river locations during the night. Typically, herons leave the Waldie area during dusk and return before dawn. The most productive foraging areas appear to be the Norns (Pass) Creek delta and the Kootenay oxbow. Studies documented the fact that during the night, fish migrate into the shallow-water areas, thus making foraging attempts at night far more productive, at least during the winter. The Waldie heron population fluctuated significantly during the study period. Maximum numbers observed at one time were 31 (2000/01), 26 (2001/02), and 21 (2002/03). When I was undertaking field studies in 1995 prior to construction of the trail, I noted 22 herons in the area. The last two years saw a further decline, with the largest number observed falling to only 8 in 2004/05. The current winter (2006/07) saw a healthy increase, with a maximum of 35 being observed at one time on Breakwater Island. Part Three: Human Conflicts and Mitigation Measures Herons are sensitive to environmental contaminants, such as dioxins from pulp mills that can lead to nest failure. Natural environmental events such as severe winter weather can result in mortality due to starvation and high wind storms can blow nests from trees. Entanglement from monofilament fishing line is a frequent human-caused accident. Illegal shooting is still a big problem. The greatest threat to overall population stability is the progressive loss of suitable nesting and foraging habitat, which may be due to human activity and/or natural causes such as aging trees. The Waldie herons are quite dependent on the lodgepole pine thickets on the island which offer preferred roosting places, as well as shelter from the elements. The loss of the more mature trees to the mountain pine beetle is a worrying development, especially if the younger trees which ring the island are destroyed. Many of the nesting sites which support the local population are on private property and are thus especially vulnerable to displacement by development. The disruptive pressures from recreational activities such as boating, jet-skiing, and motorbiking in the vulnerable areas seem to be steadily mounting. It is important that users of the Waldie Island Trail are aware of both the ecological importance and the vulnerability of the Waldie site. Of all the issues identified by the studies, one of the most pressing is that of irresponsible dog owners. When I designed and constructed the trail in 1995/96, I was very sensitive to the needs of the heron population and purposefully (and at great expense) constructed boardwalks which run through the Waldie wetland behind a screen of trees and low bushes. Unfortunately, many trail users abandon the official trail in favour of the exposed beaches during the low-water period. Such thoughtless activity is further exacerbated by dog owners who allow dogs to run loose and harass the native wildlife. The lowest water periods coincide with the nesting period of birds and many ground-nesting species at Waldie are very vulnerable to such man-made depredations. The re-establishment of a viable breeding heron colony on Waldie Island depends in part on the cooperation of people in minimizing disturbance. There are days when I wish I had never built Waldie Island Trail; however in my mind the historical values associated with this unique setting needed protection just as much as the wildlife did. Hopefully the solution is in public education, and this website is a part of my effort to do just that.
In all, several studies were commissioned by BC Hydro from 2001 to 2003. These were instrumental in convincing the Columbia Basin Fish & Wildlife Compensation Program to purchase Waldie Island in 2002 and have it set up as a protected area for the herons. I got involved early in the negotiations and in the subsequent studies for the Nature Trust of BC, who became the actual owner of the island. I was also asked to develop a preliminary management plan for the island and contributed to the development of the final management plan which was produced for the Nature Trust by Marlene Machmer. Working with the Nature Trust, I developed and installed signage which alerts the users of Waldie Island Trail to the privacy requirements for these magnificent birds, and advises that Waldie Island is out of bounds. The Nature Trust entered into a leasing agreement for the island with the Ministry of Land, Water and Air Protection in order to avoid property tax and liability obligations. Waldie Island was actually a test case for the viability of such a partnership. It is working out well. Other recommendations from the heron study reports and the Waldie Island Management Plan include the following:
Future conservation goals are outlined in the recommendations, as developed by Marlene Machmer for BC Hydro, The Columbia Basin Fish & Wildlife Compensation Program, and the Nature Trust of BC, were listed above. Some will be easier to implement than others. The most important - and probably the most workable - is public education. Waldie Island Trail is getting very popular at all times of the year and I am happy to observe that most people do not simply rush through, but do stop and read the signs, study the wildlife, and in essence loose themselves in another world. In the memorable words of Henry David Thoreau, by re-establishing such severed connections with unspoiled nature, they are coming awake from a lifetime of sleepwalking. Part Four: Personal Reflections When I was designing Waldie Island Trail I was very conscious of the fact that it would run through what is probably the most important historical location for the Castlegar area, as well as through its most important environmental asset. I sought out a balance where the visitor is exposed to facets of our history and at the same time taught to tread lightly and respect the fragility of the ecosystem which makes Waldie such a special place. The herons are only one jewel in the crown that is Waldie. As I am lucky enough to oversee the area daily from my river-side residence, I have been able to monitor closely the activity of the resident wildlife as well as of the visiting human population. The most obvious change on the river has been the increasing boat activity in the old Waldie mill pond. This relates mainly to the excellent fishing opportunities (for walleye and rainbow trout) in the mill pond area. If the summertime heron population is to be adequately protected, access into the mill pond and to the immediate vicinity of the island should be regulated, especially to motorcraft. I suggested this to Marlene, and she has incorporated it into her recommendations. Other recommendations include the incorporation of Breakwater Island and the seasonal wetland area into one overall managed heron reserve. Pedestrian traffic on Waldie Island Trail has also increased dramatically, and occasionally cyclists speed through in spite of the posted signs. It is a rewarding experience for me to observe school tours where the heritage and ecology values of Waldie are explored and sensitivity to them is being entrenched in the very young. There are many things to see. The herons may have abandoned nesting behaviour at the island, but there are still hopeful signs. On a couple of occasions I have observed "circle flights" which suggest that attempts to establish breeding pairs on the island are still being made. Probably the most dramatic events I have witnessed were interactions between herons and ospreys. On many different occasions I have been alerted by a screaming heron which had been knocked in mid-flight into the river by one or two diving ospreys. Once swimming, the bird is very vulnerable to the repeated dive-bombing attacks and its only hope lies in either the eventual abandonment of the aggression, or in its own feeble attempts to get airborne just enough to make it to the nearest shore. One such escapade was rendered all the more memorable when the protesting victim (a juvenile) was carried by the current past an adult on Breakwater Island who seemed strangely disinterested in the continued attacks. Eventually the harassed juvenile made it to the far shore of the mill pond and took shelter under some brushwood. At this point the adult flew away from Breakwater Island and landed on the beach where the juvenile was hiding, and then started patrolling the shoreline. I have only witnessed indirect interactions between herons and eagles. Eagles tend to isolate and then attack the diving ducks on the river, with their method being one of continuous hits on an unfortunate submerged duck as it tries to surface for air. Often it works as the oxygen-starved duck becomes disoriented, and then, easy prey. On one occasion I witnessed such a winter-time attack in the main river channel. As the action approached the herons which were roosting on Breakwater Island, they all left and settled on the more sheltered Waldie Island. I do not think they were threatened directly at that time by the eagles. Probably the most remarkable event I witnessed was an interaction between an osprey and a bald eagle. The latter was on the downstream point of Breakwater Island when an irate osprey started dive-bombing it. For a few passes, the eagle merely ducked at the last moment. Then the interaction became much more interesting. As the osprey commenced its dive, the eagle flapped its wings, got airborne, and inverted itself a few feet above the ground so that it could present its talons to the diving osprey just before anticipated contact. It was a remarkable feat of aeronautics, to be repeated several times. In between these climactic events, there are less dramatic things happening all the time. Flocks of goldeneyes endlessly cruise mere inches above the fast-moving river, changing shape as they fly upstream to resemble perhaps some archaic pterosaur, making love to its own reflection in the ever-shifting water. Suddenly the tinkling sounds of their wing beats cease and are replaced by light splashes as the birds settle in the medium to which they are so splendidly adapted. Drifting back with the current, they begin to feed. The cycles never cease. In having retained a portion of a free-running river, we have kept a priceless asset, which, if properly managed, can become at the same time a source of revenue for the community and a place of worship. The river for me is a vast cathedral through whose doors echo distant voices and timeless cycles, and through which run infinite numbers of inconsequential lives. It is both, a reflection of our past and our hope for the future.
Source Material: I am especially grateful to Linda Van Damme, who wrote the first section of this article, and to Wayne Campbell and Marlene Machmer for editing comments. Linda also generously provided her professional photographs for my use on the interpretive sign panel, and as illustrations for this article. A sincere thank you also goes to Gary Birch of BC Hydro, who helped me on various occasions with the heron project. BC Hydro commissioned several reports from Marlene Machmer on the Waldie herons. I have used the following reports, copies of which were provided to me by BC Hydro:
March 2002 (BC Hydro No. CA-812) November 2002 (BC Hydro No. CA-649) March 2003 (BC Hydro No. CA-675) The last document which I used was the Management Plan for Waldie Island (Draft version), which was prepared by Marlene for the Nature Trust of BC in January 2004. | ||||||||||||||||
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