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The Prothonotary Warbler in Canada: On
the Road to Recovery?
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Table of Contents
The Prothonotary Warbler is one of
the most dazzling of North American birds. Males and females look
alike, but males are more brightly coloured. They have golden yellow
heads and breasts, olive-green backs, and azure blue wings and tails.
Prothonotaries don’t have wing bars, but white tail spots
are quite prominent.
“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 1/2 ounce), and measures about 14 cm long (51/2 inches).
The male’s territorial song is a very loud, ringing “Tsweeet-tsweet-tsweet-tsweet,”
uttered emphatically in groups of four to six.
Breeding Range
The Prothonotary Warbler is the quintessential “Carolinian”
species, breeding throughout the eastern U.S. and north to southwestern
Ontario. It is most abundant in the southeastern U.S. and up the
Mississippi River.
Being at the northern edge of its range in southwestern Ontario,
the Prothonotary 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 main populations in Canada reside
on publically-protected lands in Rondeau Provincial Park, Holiday
Beach and in the Long Point region.
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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.
Most of the population is usually back on its nesting grounds by
the first week of June, but some younger females take their time
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 uses naturally formed hollows and those excavated in previous
years by chickadees and Downy Woodpeckers.
Small, shallow cavities that are situated fairly low (usually at
heights of 1-3 metres) are greatly favoured, especially if they
are over open pools of water.
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 readily
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 bottles!
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 is able to find
ample supplies of moss in its favourite habitat — swamp forests.
Indeed, the Prothonotary is very much dependent on deciduous swamp
forests. In Ontario, such swamps are typically dominated by silver
maple or buttonbush. The best Prothonotary swamps have large pools
of open standing water and little shrub cover. Prothonotaries also
frequently live 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 a hectare or
more in size.
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Why
Build “Dummy” Nests?
Male Prothonotary Warblers frequently 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 occupied. Finally, the “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 or two laying the foundation for the functional
nest, it saves her time in nest building, and thus gives her a jump-start
on the all-too-short nesting season.
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Nesting is What it's All About
By late May and early June, many of Ontario’s
Prothonotaries have established territories and
finished making their nests. For a songbird, the
Prothonotary lays an unusually large number of
eggs. The normal clutch is 5 to 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 green caterpillars to snack on, when he isn’t
too busy chasing away avian intruders or incessantly singing.
The eggs usually hatch in about 12 days and the parents are kept
busy for another 10-12 days feeding the insatiable young. Again,
green caterpillars are a particular favourite. On this protein-rich
diet, the young grow quickly, and the nest cavity rapidly fills
up with baby Prothonotaries. Because the cavity is small and shallow,
and because the Prothonotary family is often 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 dangerous first flight. The
nestlings haven’t been able to exercise their wings, so the
best they can muster at this age is a short hop of only a few metres.
Because the inaugural flight is invariably over open water and since
Prothonotaries aren’t built for swimming, they need to land
on the nearest branch.
When one of the youngsters finally gathers the courage to fledge,
the rest promptly follow the leader. Upon landing in a nearby low-hanging
branch, the fledglings call incessantly to their parents, and then
quickly begin working their way up the tree — branch by branch
— to the highest parts of the tree canopy. In no time at all,
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 been in
Canada for only about 3 months. It is no wonder that “our”
birds are considered to be “their” birds by the people
of Latin America, where Prothonotaries actually spend the majority
of their lives.
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Winter in Latin America
Prothonotaries migrate south to the U.S. Gulf Coast and then make
a hazardous non-stop flight 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 and other lowland 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.
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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 of Prothonotaries had been
reduced to no more than about 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 Prothonotary
Warbler is still abundant in its core breeding 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 Prothonotary in Canada began in 1997, and
there are some encouraging signs that the species is responding
positively. In 2000, the adult population was estimated to consist
of up to 22 mated pairs, plus an additional 8 unmated males, for
a total of 52 adult birds.
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Limiting Factors
Why is the North American population of Prothonotary Warblers declining?
A combination of things is probably responsible. Loss of both breeding
and wintering habitat are primary concerns. Increasing populations
of nest site competitors, nest predators, and nest “parasites”
(i.e. Brown-headed Cowbirds) 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. Several of the formerly
occupied sites have also been degraded by logging. More insidious,
sustained high water levels on Lake Erie during most of the 1980s
and 1990s caused trees to die-back in several of the most important
lakeshore sites, effectively turning forest swamp into scrubby marshes
that are no longer very suitable for Prothonotaries. At the other
extreme, severe droughts dry up swamp forests.
In the U.S., habitat loss and degradation are of great concern,
especially in the southeastern states that support the “core”
breeding population of Prothonotaries. 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.. Over 6% of the forested swampland in the U.S. was drained
and/or converted to other uses in the last decade alone, and most
of this loss occurred in the southeastern states. Loss of breeding
habitat in the U.S. has probably been responsible for the elimination
of about 20% of the North American Prothonotary Warbler population
since 1966.
While loss of habitat on the breeding grounds is undoubtedly contributing
to the Prothonotary Warbler’s declining population, loss of
wintering habitat — especially mangrove forest — in
Latin America is perhaps even a greater problem. It is estimated
that as much as 30% of the species’ wintering habitat has
been destroyed since 1966, and the rate of loss has been accelerating
alarmingly in the last two decades.
Mangrove forest, which provides winter habitat to the bulk 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.
Mangrove ecosystems are also under pressure from pesticide contamination
(including DDT) and oil pollution. Ultimately, without efforts to
save this critical habitat, the future of the Prothonotary Warbler
(and numerous mangrove-dependent species of fish and wildlife) is
worrying.
Meanwhile, back on the breeding grounds, the chief competitors
that the Prothonotary Warbler faces for nest sites are Tree Swallows
and House Wrens. Numbers of both of these species are normally quite
small in large blocks of undisturbed forest. However, their populations
quickly increase in response to forest fragmentation and in response
to logging or natural events that open up the tree canopy cover.
In places where these competitors are common, they usurp many Prothonotary
nests, and can have a very serious and long-term impact on local
populations. “Vandalism” caused by House Wrens destroys
many Prothonotary nests and eggs.
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, populations of
which have increased dramatically in southern Ontario in recent
decades.
When you put all these things together, you can see that the Prothonotary
Warbler faces an uphill battle.
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What the Recovery Team is Doing
The Prothonotary Warbler Recovery Team is a multi-agency group,
with representatives from non-government organizations, private
stakeholders,and federal and provincial governments. Established
in 1997, one of its first tasks was to prepare a recovery plan.
The goals of the plan are to ensure that the Prothonotary Warbler
does not become extirpated in Canada, and to increase the population
to at least 25 mated pairs.
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; 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 raccoons.
The program consists of over 200 nest boxes that have been erected
in suitable habitat in most of the historic breeding locations in
southwestern Ontario, and in a few other promising locations. Early
results from the program are encouraging — the birds are readily
accepting the boxes. Moreover, because the nest boxes afford protection
against predators and cowbird parasitism, they are fledging more
young than birds nesting in natural cavity situations.
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A male
Prothonotary Warbler at one of the recovery team’s nest
boxes / J. McCracken |
While we have learned a lot about the problems faced by Prothonotary
Warblers, there are still some key questions that need to be answered.
The recovery team 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.
The recovery plan also addresses broader issues related to habitat
protection and forest management practices in Canada, the U.S. and
Latin America. Providing information to the general public, landowners,
land managers, and policy makers are other activities that the recovery
team is increasingly involved in.
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What You Can Do
- The Prothonotary Warbler is understandably sought after by birders
and wildlife photographers. While the Prothonotary is relatively
tame and tolerates moderate amounts of human company, it is sensitive
to human disturbance around its nest site. Remember that the Prothonotary
is an endangered species in Canada, so please enjoy it from a
distance. Try to stay at least 15 metres 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. Also, refrain from broadcasting song recordings to try to
lure the bird into the open.
- Decayed tree stubs that are home to Prothonotaries can be so
rotten and fragile that they can easily topple over if you brush
against them.
- You can help the Recovery Team by offering to build predator
guards and/or nest boxes. The nest box program follows specific
guidelines, so be sure to contact the Team before considering
installing boxes on your own.
- 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!
- Consider making a monetary donation to directly support the
work of the Recovery Team.
- Remember that the prawn aquaculture industry is being increasingly
implicated in the destruction of mangrove forests, and that this
endangered habitat provides a critical winter home for Prothonotaries.
Continue to enjoy eating shrimp, but try to avoid those raised
by aquaculture operations that destroy mangrove forests.
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Information for Landowners
- 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
plants and animals, several of which are of conservation concern.
By not draining swamps, you also maintain your local water table,
which has dropped dramatically in many areas in recent years.
Landowners may even wish to reflood previously drained swamp forest,
but be sure to consult with your neighbors and local municipality
first.
- In order to protect Prothonotaries, swamps need to be protected
from logging. Logging opens up the tree canopy, which attracts
nest site competitors and cowbirds. The extra light penetration
also kills mosses, robbing the Prothonotary of essential nesting
material. It also results in the proliferation of shrubs and marshy
vegetation, which close-in the pools of open water that Prothonotaries
require.
- It is important to retain all standing dead trees for nest sites,
so even fuel-wood cuts in Prothonotary Warbler swamps need to
be avoided.
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About Ontario's Endangered Species
Act
In 1999, the Prothonotary Warbler was designated as
an endangered species under Ontario’s Endangered
Species Act. This Act provides legal protection to the bird,
its nest and eggs, and its nesting habitat in Ontario. The habitats
of endangered species in Ontario are classified as “Conservation
Lands” for which landowners may apply for an exemption from
municipal property taxes.
Landowners whose properties contain Prothonotary Warbler
habitat are eligible to apply to participate in Ontario’s
Conservation Land Tax Incentive Program (CLTIP). This program offers
100% tax relief to landowners for the portion of their property
that is considered to be endangered species habitat. Under the Provincial
Policy Statement, the CLTIP also offers tax relief to owners of
provincially significant wetlands, which could provide protection
of Prothonotary Warbler habitat at a broader scale. Contact your
local District Office of the Ontario Ministry of Natural Resources
for details.
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More Information . . .
For more information about the Prothonotary
Warbler or the activities of the recovery team, contact:
- Bird Studies Canada
P.O. Box 160, Port Rowan, Ontario N0E 1M0
Tel: 519-586-3531 or
Toll free at 1-888-448-2473;
Email: generalinfo@bsc-eoc.org;
Web site: www.bsc-eoc.org
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- Ontario Ministry of Natural Resources
P.O. Box 1168, Chatham, Ontario N7M 5L8
Tel: 519-354-4108
- Canadian Wildlife Service - Ontario Region
49 Camelot Drive, Nepean, Ontario K1A 0H3
Tel: 613-952-2417
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ACKNOWLEDGMENTS: This pamphlet
and the work of the Prothonotary Warbler Recovery Team have been
supported by the following sponsors and partners: Bird Studies Canada,
Canadian Wildlife Service, Endangered Species Recovery Fund, McBride
Foundation, Millennium Partnership Program, Mountain Equipment Co-op,
Natural Heritage Information Centre, Ontario Ministry of Natural
Resources, Ontario Parks, Shell Environmental Fund, and World Wildlife
Fund Canada.
© 2001 Bird Studies Canada
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