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The Prothonotary Warbler in Canada |
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Description The Prothonotary Warbler is one of the most dazzling of North American birds. Males and females look alike, but males are somewhat more colourful. They have golden yellow heads and breasts, yellow-green backs, and azure blue wings and tails. Prothonotaries don’t have wing bars, but white tail spots are quite prominent. The Prothonotary Warbler may be confused with the Yellow Warbler, which is almost all yellow, with rusty streaks on its breast. The Blue-winged Warbler also looks similar, but it has a black streak through its eye and whitish wing bars. "Prothonotary" is a big name for such a little bird. Human prothonotaries are religious and legal clerks who sometimes wear a golden hood and a blue cape. The Prothonotary Warbler is also known as the "golden swamp warbler" in some regions. For a warbler, the Prothonotary Warbler has quite a long bill — one of the diagnostic features that places it in its very own scientific genus (Protonotaria). The average Prothonotary weighs about 14 grams (about ½ oz), and measures about 14 cm long (5 1/2 inches). Its territorial song is a very loud, memorable, ringing "Tsweeet-tsweet-tsweet-tsweet," uttered in groups of four to six. Thus, together with its yellow colour, the Prothonotary is "Tweety Bird" come to life!
Breeding Range The Prothonotary is the quintessential "Carolinian" species, breeding throughout the eastern U.S, and north to extreme southwestern Ontario. It is most abundant in the southeastern U.S. and up the Mississippi River. Being at the fringe of its range in southwestern Ontario, the Prothonotary Warbler is almost entirely restricted to a few areas on and adjacent to the Lake Erie shoreline (Holiday Beach, Pelee Island, Point Pelee, Wheatley, Rondeau, Long Point, and Point Abino). It also regularly occurs in Hamilton, and occasionally nests at Pinery Provincial Park on Lake Huron. The "core" populations in Canada reside in Rondeau Provincial Park and the Long Point region.
Prothonotaries in the Spring In spring, the Prothonotary begins to return to southern Ontario in the first week of May. Males generally precede females by about 2 weeks, and older birds of both age groups precede younger ones. The entire adult population is usually back on its nesting grounds by the first week of June, but some younger females dilly-dally and may not arrive until the end of June. By the time the females are back, the males have already established their territories and begun to select potential nest sites for the females to inspect. The Prothonotary is the only warbler in eastern North America that builds its nests in tree cavities. Since it cannot excavate its own, it happily uses naturally formed hollows and those excavated in previous years by chickadees and Downy Woodpeckers. Cavities that are fairly low (usually 1-3 metres) are greatly favoured, especially if they are over open pools of water. Other than that, Prothonotaries are not terribly fussy about the cavity. In fact, Prothonotaries have been known to use some pretty strange nesting sites, including a tool box, the pocket of an old coat, a paper sack, a coffee can, a tin pail, a mail box, a box on a moving ferry, a Chinese lantern, an old hornet’s nest, a glass jar, and a tea cup. Like many other cavity-nesters, Prothonotaries also love to nest in bird boxes, both traditional wooden ones, and others that are made of more unusual materials. For example, one nest box program in Michigan uses wax cardboard milk containers with great success, while another program in Ohio uses plastic Metamucil bottles (donated by a local senior citizen’s centre)! Whatever the cavity, Prothonotaries fill it almost to the brim with green moss, usually mixed with a few dead leaves. The nest is lined with fine grasses and rootlets. It is thought that the green moss acts as a natural fumigant to suppress lice infestations and that it also helps keep the nest insulated against temperature extremes. In any case, the Prothonotary Warbler will not inhabit an area unless it has an ample supply of moss. Swamp forests are great spots for the proliferation of mosses.
Why Build Dummy Nests? More often than not, the male will build one or more incomplete or "dummy" nests, adding just a shallow layer of moss to cavities scattered within its territory. These partial nests appear to serve several functions. First, the male may use them to demonstrate to the female that he has chosen a good territory with lots of nesting opportunities. He may also be trying to fool potential predators into thinking that cavities with nests do not necessarily mean a free lunch. As well, he is informing other nest competitors (House Wrens, Tree Swallows and other male Prothonotaries) that his territory is "full." There is some evidence that the male may use the "dummy" nests as night-time roosting sites. Finally, a "dummy" nest is quite often adopted by the female upon her arrival, who then takes over completing the functional nest. Because the male has already spent a day laying the foundation for the functional nest, it saves her a day in nest building, and thus gives her a jump-start on the all-too-short nesting season. Nesting is What it’s all About By late May and early June, many of the province’s Prothonotaries have established territories and completed their nests. For a songbird, the Prothonotary lays an unusually large number of eggs, one day at a time. The normal clutch is 6 eggs, but 8-egg clutches are also fairly common. The female does all of the incubation. The male tends her on the nest by bringing her tasty green caterpillars to munch on, when he isn’t too busy chasing away avian intruders or incessantly singing. The eggs usually hatch after about 12 days and the parents are kept busy for about another 10-12 days feeding the insatiable young. Again, tasty green caterpillars are a particular favourite. On this protein-rich diet, the young grow very quickly, and the nest cavity quickly fills up with baby Prothonotaries. Because the cavity is usually very small and shallow, and because the Prothonotary family is usually a big one, there isn’t room for anybody to exercise their growing wings, let alone stretch! Owing to the crowded conditions, the young leave the nest as soon as they’re able to. This is a very difficult first flight. Not only are the youngsters incapable of sustained flight (the best they can muster at this age is a few metres), but their first flight is almost always directly over open water. Prothonotaries aren’t built for swimming, so the first flight better land them on the nearest branch, or else they will drown. Also, because of the crowded nest, the young haven’t been able to exercise their wings at all, so they are making their inaugural flight fueled by sheer guts and determination. When one of the youngsters finally gathers his or her courage to fledge, the rest quickly follow the leader. They invariably land in a nearby low-hanging branch, and begin to call incessantly to their parents. They instinctively work their way up the tree, branch by branch, to the highest parts of the tree canopy. Within a half hour or so, they are high up, and nearly impossible to see from the ground. For the next month or so, they become tree-top birds, perhaps because this gets them out of the way of marauding mammalian predators. If this all happens before mid June, there is a chance that the parents will attempt a second nesting. In Ontario, however, the Prothonotary Warbler usually has only enough time to bring off one brood of nestlings. By mid August, nearly all of Ontario’s Prothonotary Warblers are beginning to migrate southward to their wintering grounds in Latin America. All told, our family of Prothonotaries has only been in Canada for about 3 months. It is no wonder that "our" birds are considered to be "their" birds by the people living in Latin America, where Prothonotaries actually spend the majority of their lives. The Winter Prothonotaries migrate south to the U.S. Gulf Coast and then make a relatively short hop across the Gulf to land in central America and northern South America. The bulk of the population winters in the coastal lowlands of Panama, northern Venezuela and northern Colombia, where it is concentrated in mangrove forests. Hence, a very large breeding population is effectively compressed into a relatively small geographic area during the winter. It is easy to see how the Prothonotary Warbler’s population is particularly vulnerable on the wintering grounds, whether it arises from natural disasters such as hurricanes, or from human-caused changes in the coastal environment. In fact, mangrove ecosystems are among the most threatened in the world.
Population Size and Trend In the early 1930s, the Ontario population of Prothonotary Warblers probably consisted of about 100 to 150 pairs, most of which were located at Rondeau Provincial Park. By the mid 1980s, there were still as many as 80 pairs left in the province, and the species was considered "vulnerable" in Canada. Population monitoring based upon the continental Breeding Bird Survey shows that serious declines began to take hold by the late 1980s. By 1996, the Ontario population had been reduced to no more than 20 birds (10 pairs), and the species jumped from being "vulnerable" to "endangered" in Canada. Meanwhile, south of the border, U.S. scientists listed it as a species of special conservation concern. Although the species is still abundant in its core range in the southeastern U.S., scientists estimate that the continental population has declined by an average rate of -1.6% per year since 1966. At first glance, this doesn’t sound like much, but it translates to a loss of about 50% over just 30 years. Efforts to restore the species in Canada began in 1997, and there are some encouraging signs that the species is responding positively. In 1998, the adult population was estimated to consist of up to 17 mated pairs, plus an additional 10 unmated birds, for a total of 44 birds.
Limiting Factors Why is the North American population of Prothonotary Warblers declining? A combination of things is probably responsible. Loss of breeding habitat, especially in the southeastern U.S., has been a primary concern. But this problem has been recently eclipsed by the loss of winter habitat in coastal Latin America. In addition, increasing populations of nest site competitors, mammalian predators and nest parasites are also believed to contribute to the decline. Although the rate of wetland loss has slowed in recent decades, southern Ontario has still lost about 70% of its original wetlands, much of which was formerly forested swampland. Most of this loss has been brought about by drainage practices, but some of the loss has also been due to development activities. For example, as recently as 1978, a forest swamp at Turkey Point that was occupied for many years by Prothonotaries was filled and turned into a trailer park. In 1996, one site that supported Prothonotaries was excessively logged and the birds have not returned. Logging activities at another site in 1997 may also have affected local Prothonotary Warbler populations. More insidious, sustained high lake levels during most of the 1980s and 1990s have also contributed to tree die-back in several of the most important lakeshore sites, effectively turning forest swamp into scrubby marshes that are no longer suitable for Prothonotaries.. In the U.S., habitat loss and degradation are of even greater concern, especially in the southeastern states that support the "core" population of this species. Because these core populations act as important sources for the maintenance of outlying populations, their declines are especially troublesome. Despite tremendous conservation efforts, forest swampland is still under intense pressure in the U.S., especially in the southeast. Over 6% of the forested swampland in the U.S. was drained and/or converted to other uses in the last decade, and most of this loss occurred in the southeastern states. Based upon the estimated amount of breeding habitat that has been destroyed in the U.S. since 1966, this loss has probably been responsible for the elimination of about 20% of the North American Prothonotary Warbler population. While loss of habitat on the breeding grounds is undoubtedly a contributing factor to the Prothonotary Warbler’s declining population at the continental level in recent decades, loss of wintering habitat, especially mangrove forest, in Latin America is perhaps even a greater problem. There are no good estimates of the amount of wintering habitat that has been lost, but it is likely somewhere around 30% since 1966, and the rate of loss has been accelerating alarmingly in the last two decades. Mangrove forest, which provides winter habitat to about 80% of the Prothonotary Warbler population, is regarded as one of the world’s most threatened habitats. It is being destroyed to make way for shrimp aquaculture and coastal resort developments, and is under increasing pressure from the charcoal industry. As well, coastal developments like roads, dykes and channelization interfere with nutrient exchange, and increase siltation rates and salinization, which have resulted in massive die-backs of mangrove in many areas. Finally, mangrove ecosystems are also under pressure from widespread pesticide contamination (including DDT) and oil pollution. Ultimately, without efforts to save this critical habitat, the future of the Prothonotary Warbler (and numerous resident species of fish and wildlife) is questionable. Meanwhile, back on the breeding grounds, the chief competitors that the Prothonotary Warbler faces for nest sites are Tree Swallows and House Wrens. In places where these competitors are common, they usurp many Prothonotary nests, and can have a significant and long-term impact on local populations. Even though the Prothonotary nests in tree cavities, roughly a third of its nests in Ontario are parasitized by Brown-headed Cowbirds, a species that has only recently invaded eastern North America. The most conspicuous nest predator is the raccoon, but House Wrens also destroy some Prothonotary nests and eggs. Populations of raccoons have increased dramatically in southern Ontario in recent decades. When you put all these things together, you can see that Prothonotary Warbler faces an uphill battle. What the National Recovery Team is Doing Chaired by Bird Studies Canada, the Prothonotary Warbler Recovery Team is a multi-agency group, with representatives from the Ontario Ministry of Natural Resources and the Canadian Wildlife Service. One of its first tasks was to prepare an official recovery plan. Simply put, the goals of the plan is to ensure that the Prothonotary Warbler does not become extirpated in Canada, and to increase the population to at least 20 mated pairs by the end of 2001. The plan will evaluated at the conclusion of its first 5 years, when it will be decided whether our recovery efforts have been successful, and whether they should be continued or modified. Through a carefully-planned nest box program, the Recovery Team is attempting to address four of the limiting factors faced by Prothonotaries on their Canadian nesting grounds: 1) a general shortage of suitable cavity nest sites in some of the core nesting areas in Ontario, 2) a high level of interspecific competition for natural cavity nest sites from Tree Swallows and House Wrens, 3) a high rate of cowbird parasitism, and 4) a high rate of nest predation by mammalian predators, especially raccoons.
The recovery plan also addresses broader issues related to habitat protection and forest management practices in Canada, the U.S. and Latin America. Education of the general public, landowners, land managers, and policy makers are other activities that the recovery team is increasingly involved in. Using some of the most experienced bird banders in North America, the team also plans to band the majority of the Canadian population of Prothonotary Warblers, using special colour bands, to determine population turnover, site faithfulness, and the extent to which the Ontario population is augmented by birds from the U.S. 1. The Prothonotary Warbler is one of the most beautiful of all songbirds, and is understandably much sought after by birders and wildlife photographers. While the Prothonotary is relatively tame and tolerates moderate amounts of human company, it is quite sensitive to human disturbance around its nest site. Remember that the Prothonotary is a critically endangered species in Canada, so please enjoy it from a distance. Try to stay at least 15 metres (about 20 yards) away from any known nest site. If the birds start to chip excitedly, it means that you’re too close. These alarm calls can alert possible predators to the nest site, and result in nesting failures. For photography, use a telephoto lens (300 mm or larger), and very fast film (ASA 400 is recommended owing to poor light conditions in swamp forests). 2. Nests in natural cavities in decayed tree stubs are often so rotten and fragile that they can easily topple over if you brush against them! 3. You can help the recovery team by offering to build nest boxes and predator guards. 4. Report your sightings of Prothonotary Warblers to the Recovery Team, at all times of the year, even on the wintering grounds! Your sightings are very important! If you see a Prothonotary Warbler with a leg band, report the details immediately to Bird Studies Canada, paying very close attention to the position and colour sequence of the bands. 5. Consider joining Bird Studies Canada to support the work of the Prothonotary Warbler Recovery Team. 6. Remember that the growing prawn aquaculture industry is being increasingly implicated in the destruction of mangrove forests around the world, and that this endangered habitat provides a critical winter home for Prothonotaries. Continue to enjoy eating shrimp, but try to avoid those raised by the aquaculture industry. Even then, as an informed consumer, you may wish to cut back on your consumption of those all-too-tempting, all-you-can-eat specials! Forest Management Guidelines for Landowners 1. Most of the deciduous swamp forest in southwestern Ontario has already been drained, and it is especially important to maintain what little we have left. Deciduous swamps are home to many wetland-dependent species, several of which are of conservation concern. For example, Louisiana Waterthrushes, Northern Waterthrushes, Cerulean Warblers, Acadian Flycatchers, Wood Ducks, Spotted Turtles, and multitudes of frogs and salamanders all rely upon forest swamps. By not draining swamps, you also maintain your local water table, which has shown dramatic declines in many regions in recent years. Landowners may even wish to consider reflooding previously drained swamp forest, but be sure to consult with your neighbours and local municipality first. 2. In order to protect Prothonotaries, you should avoid doing any logging in these wetlands. Logging opens up the tree canopy, which attracts nest site competitors (swallows and wrens), predators and cowbirds. The extra light penetration kills mosses, robbing the Prothonotary of essential nesting material and also results in the proliferation of shrubs and marshy vegetation like cattail and phragmites, which close in the pools of open water that Prothonotaries (and many other species) require. 3. It is especially important to retain all standing dead trees for nest sites, so even fuel-wood cuts in Prothonotary Warbler swamps should be avoided. 4. If you feel that you simply must do a forest harvest, make it as light as possible. If heavy equipment is involved, restrict it to the deep winter when the ground is thoroughly frozen. Acknowledgements The activities of the Prothonotary Warbler Recovery Team are chaired by Bird Studies Canada, in partnership with representatives from the Ontario Ministry of Natural Resources (OMNR) and the Canadian Wildlife Service-Ontario Region (CWS). The team’s work has been generously supported by the Ontario Ministry of Natural Resources, Canadian Wildlife Service, Bird Studies Canada, Environment Canada’s Eco-Action 2000 fund, Lever Pond’s, World Wildlife Fund, and the Endangered Species Recovery Fund. Additional financial support from the McBride Foundation, and personal donations from Robert Bateman (through the Ontario Eastern Bluebird Society) and Don McGeachy are gratefully acknowledged. Last but not least, we thank in-kind donations of materials and labours of love from Don Wills and a great number of other people from the Norfolk Field Naturalists, St. Thomas Field Naturalists, Vittoria Boy Scouts, Rondeau Provincial Park, Point Pelee National Park, Holiday Beach Provincial Park, Long Point Region Conservation Authority, Essex Region Conservation Authority, and numerous private landowners. For further information, please contact: Jon McCracken, Chair
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On
the Road to Recovery?
Prothonotary Warbler
Yellow Warbler
Blue-winged Warbler
Indeed,
the Prothonotary is very much dependent on deciduous swamp forests that are typically
dominated by silver maple or buttonbush. Prothonotary swamps always have large expanses of
open standing water and little shrub cover. Prothonotaries also frequently occur along the
margins of slow-moving, warm-water creeks and rivers, lined with large willows.
Territories are large and well-defended, and usually encompass about 2 hectares (e.g. 100
metres by 200 metres). This means that very small pools of open water swamp are
insufficient; the open water area required for each pair is almost always at least 1
hectare in size.
The
program consists of about 200 nest boxes that have been erected in suitable habitat in
most of the historic breeding locations in southwestern Ontario, and a few other promising
locations. Early results from the program are very encouraging — the birds are
readily accepting the boxes. For example, 17 of 21 Prothonotary Warbler nests in 1998 were
in our nest boxes. Even more importantly, because of the protection afforded by the nest
boxes, they are fledging more young than birds in natural cavity situations. And the
Canadian population has increased from about 20 adult birds in 1996 to 44 adults in 1998.