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Recovery Strategy for the Prothonotary Warbler (Protonotaria citrea) in Canada [Proposed]

1. Background


1.1 Species Assessment Information from COSEWIC

Date of Assessment: May 2000


Common Name: Prothonotary Warbler


Scientific Name: Protonotaria citrea

COSEWIC Status: Endangered


Reason for Designation: This species is facing a significant range-wide decline primarily due to habitat loss and degradation. It has undergone a drastic decline in Ontario where it is estimated that there are currently only 13 pairs at two sites.


Canadian Occurrence: ON


COSEWIC Status History: Designated Special Concern in April 1984. Status re-examined and designated Endangered in April 1996. Status re-examined and confirmed in May 2000. Last assessment based on an existing status report.

1.2 Description

The Prothonotary Warbler is one of North America’s most dazzling songbirds. Males and females look alike, but males are decidedly more brightly coloured. Both have golden yellow heads and breasts, olive-green backs, and azure blue wings and tails. Prothonotary Warblers do not have wing bars, but white tail spots are quite prominent. Although rather large for a warbler, Prothonotary Warblers are small birds, weighing about 14 g and measuring about 14 cm in length. The male’s territorial song is a loud, ringing “tsweeet-tsweet-tsweet-tsweet,” uttered emphatically in groups of four to six.

1.3 Populations and Distribution

The continental population of the Prothonotary Warbler is estimated to consist of about 900 000 pairs[1] (Rich et al. 2004), over 99% of which reside in the United States. Globally and in the United States, the species is considered secure (NatureServe 2006), but has sub-national conservation ranks varying from critically imperilled to secure (Table 1). According to results from the Breeding Bird Survey (Sauer et al. 2005), the continental population has experienced a significant decline, averaging −1.5% annually during the period 1966–2004, or about 44% overall.

Less than 1% of the Prothonotary Warbler’s global population occurs in Canada. The Canadian population is ranked critically imperilled to imperilled (NatureServe 2006). Canada currently supports fewer than 20 pairs, down from an estimated 40+ pairs during the mid-1980s.

Table 1. Sub-national conservation ranks (S-ranks) in Canada and the United States for the Prothonotary Warbler (NatureServe 2006)
CountrySub-national conservation ranks
United StatesAlabama (S5B), Arizona (S1M), Arkansas (S4B), Colorado (SNA), Connecticut (SNA), Delaware (S4B), District of Columbia (S1B), Florida (SNRB), Georgia (S5), Illinois (S5), Indiana (S4B), Iowa (S3B,S3N), Kansas (S3B), Kentucky (S5B), Louisiana (S5B), Maryland (S4B), Massachusetts (S3), Michigan (S3), Minnesota (SNRB), Mississippi (S5B), Missouri (S4), Nebraska (S2), New Jersey (S4B), New Mexico (S4N), New York (S2), North Carolina (S5B), Ohio (S3), Oklahoma (S4B), Pennsylvania (S2S3B), Rhode Island (S1B,S1N), South Carolina (S3B), South Dakota (SNA), Tennessee (S4), Texas (S3B), Virginia (S4), West Virginia (S2B), Wisconsin (S3B)
CanadaOntario (S1S2B)

S1 – critically imperilled; S2 – imperilled; S1S2 – critically imperilled to imperilled; S2S3 – imperilled to vulnerable; S3 – vulnerable; S4 – apparently secure; S5 – secure; SNR – unranked; B – breeding population; N – non-breeding population; M – migrant/transient population; SNA – conservation status not applicable because the species is not a suitable target for conservation activities

The Prothonotary Warbler breeds throughout the eastern United States and north to southwestern Ontario (Figure 1). It is most abundant in the southeastern United States and up the Mississippi River. Its wintering range extends from southern Mexico through Central America and northern South America. Its centres of abundance are reported to include northern Venezuela, Colombia (Bent 1953; Lefebvre et al. 1992, 1994), and coastal Panama (Lefebvre and Poulin 1996). However, extensive quantitative surveys of wintering populations in different regions have not been conducted.

Breeding and wintering range of the Prothonotary Warbler

Figure 1. Breeding and wintering range of the Prothonotary Warbler

Being at the northern edge of its range in southwestern Ontario, the Prothonotary Warbler has been found primarily along and adjacent to the Lake Erie shoreline (e.g. Holiday Beach, Pelee Island, Point Pelee National Park, Wheatley Provincial Park, Rondeau Provincial Park, Long Point, and formerly Point Abino; Figure 2). Nesting has occurred regularly at one site along the Lake Ontario shoreline (Hamilton) and rarely at one site along the Lake Huron shoreline (Pinery Provincial Park). The Prothonotary Warbler also occasionally nests in some inland sites in southwestern Ontario. It formerly nested at Turkey Point, near London (at Lobo), and near Orwell and Copenhagen.

Current and historic breeding occurences of Prothonotary Warblers  in Canada

Figure 2. Current and historical breeding occurrences of Prothonotary Warblers in Canada

1.4 Description of the Species’ Needs

1.4.1 Biological needs, habitat needs, ecological role, and limiting factors

Prothonotary Warblers return to Ontario from wintering areas in the first week of May; females typically arrive about two weeks later than males, and older birds of both sexes usually precede younger birds. The entire adult population is usually on its nesting grounds by the first week in 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 Warbler is the only warbler in eastern North America that builds its nests in tree cavities. The species is a secondary cavity nester, meaning that it does not excavate its own cavities, but instead uses cavities that were created naturally or by primary cavity nesters. Most commonly, they occupy cavities that have been excavated by chickadees (Poecile sp.) and Downy Woodpeckers (Picoides pubescens). Males often build one or more incomplete “dummy” nests (Bent 1953; Petit 1989; Blem and Blem 1992). Dummy nests are non-functional nests whose quantity and quality are potentially important influences on pair formation (Petit 1999). The female often selects one of these dummy nests to complete, but may also build an entirely new nest on her own. Clutch size is usually about six eggs, but is often eight, and the female will lay only one egg per day. She alone incubates the eggs for approximately 12 days, while the male tends to her with food. Both parents feed the nestlings for about 10–12 days. On their first flight, fledglings risk drowning in water that is usually under the nest while attempting to make it to the closest shrub. Throughout the breeding season, adults and juveniles depend on a wide variety of insects and molluscs (snails); the bulk of food taken includes larvae of butterflies and moths, flies, beetles, spiders, and mayflies (Petit 1999). By mid-August, nearly all birds will have begun their migration south for the winter.

Availability of nesting sites is a known limiting factor for this species. The Prothonotary Warbler is not a serious competitor for cavity nest sites in Canada. Owing to its very small population size in Canada, this species does not likely fill any major ecological role here. More details of specific habitat elements are provided below.

Presence of standing or slowly flowing water – Typically, territories are almost entirely covered with standing water (e.g. permanent and semi-permanent pools of open water in swamp forests along the shore of, or inland from, the Great Lakes) or slowly flowing water (e.g. as found in wide, slow-moving, warm-water forested creeks draining into the Great Lakes). During the nesting season, optimal water depth near nests ranges from 0.5 to 1.5 m, and the surface area of water represents between 70% and 100% of the territory. Pools in these territories may be 1 ha or more in size, although sites containing smaller pools will also be occupied if several pools are in close proximity. Nests are nearly always situated over or within 5 m of standing water or in low-lying, easily flooded areas (Petit 1999). The most productive territories are inundated year-round, but the warbler will nest in seasonal sloughs that may dry up entirely by mid- or late summer. Water cover that is sustained from May through at least mid-June is important.

Swamp forest– In Ontario, Prothonotary Warblers occupy mature and semi-mature deciduous swamp forest and riparian floodplains. Tree cover is typically dominated by silver maple (Acer saccharinum), ash (Fraxinus spp.), yellow birch (Betula alleghaniensis), and willows (Salix sp.) (McCracken and Dobbyn 1997). The extent of canopy cover depends on water depth and duration of flooding, but ranges from 20% to 90%, averaging slightly more than 50%, and is usually extensive enough to limit the development of a herbaceous and shrubby plant understorey. Nest sites are usually shaded for at least part of the day (Blem and Blem 1991, 1992; Best and Fondrk 1995). The shrub layer of the swamp forest is usually poorly developed because of low light levels and deep water, although some shrubs or saplings are usually in the immediate vicinity of the nest. In more open, deep-water habitats, mature buttonbush (Cephalanthus occidentalis) often dominates. A shrub or sapling located within a few metres of a nest provides immediate refuge for fledglings.

Open swamps with extensive emergent herbaceous vegetation are generally avoided by Prothonotary Warblers. Occasional scattered patches of cattails (Typha sp.), common reed (Phragmites australis), grasses, and sedges will frequently occur in the territory, but are not usually dominant cover types, particularly early in the nesting season (May to mid-June). Emergent vegetation around nest sites is usually sparse (open water is generally a dominant feature).

Forest size – Little information is available about the effects of woodland size or forest fragmentation on Prothonotary Warblers. The Prothonotary Warbler was described as an area-sensitive species by Keller et al. (1993), Petit (1999), and Thompson et al. (1993), but not by Robbins et al. (1989) or Hodges and Krementz (1996). In riparian forests in the southeastern United States, populations of Prothonotary Warblers and other forest wetland birds can probably be conserved if a 100-m-wide corridor of suitable habitat is protected (Hodges and Krementz 1996), whereas Kilgo et al. (1998) found that the probability of occurrence for Prothonotary Warbler was greatest in forests that were at least 500 m wide. In Canada, nearly all known breeding sites occur within forest tracts that are at least 25 ha.

Dead or dying trees with cavities – As noted above, cavities chosen by Prothonotary Warblers are almost always directly above water. Several suitable cavities appear to be required in each territory, in order to accommodate both the functional nest plus one or more “dummy” nests. The number of cavities within 25 m of a nest ranges widely, from 1 to 10 (mean = 2.3) (McCracken and Dobbyn 1997). When tree cavities are used, they are small and shallow (a volume of about 1.0–1.5 litres) and located 0.5–2.5 m above the water.

Suitably designed artificial nest structures (e.g. wooden nest boxes) are readily accepted by the species and perhaps even preferred (e.g. Best and Fondrk 1995; McCracken and Wood 2005). Prothonotary Warblers have also occasionally been known to nest in such unusual situations as a coffee can, tin pail, glass jar, an old hornet’s nest, and a mailbox (Bent 1953).

Availability of nest material – Green mosses and dead leaves, as well as fine rootlets, lichens, and grasses, are used for building and lining both incomplete and functional nests. Habitats with plentiful moss are clearly favoured. Mosses are typically most abundant in swamps that have a long history of flooding, especially where canopy cover provides shade sufficient for moss growth. Moss is considered a limiting factor, but there is no information on whether a particular species of moss is favoured.

Post-fledging habitat – No published studies are available concerning the characteristics of the Prothonotary Warbler’s habitat needs once the young have left the nest. Nevertheless, there is evidence that fledged young range widely, often occupying the upper tree canopy within 300 m or more of the nest site for at least one month, regardless of the presence of standing water (J.D. McCracken, pers. obs.). Hence, once the young fledge, the species can and will occur anywhere within a forest tract, including dry upland portions. By and large, the species appears to become a bird of the upper canopy during this period, probably favouring trees that are at least 15 m in height (J.D. McCracken, pers. obs.).

Wintering habitat – The Prothonotary Warbler’s key wintering habitat is coastal mangrove forest in Central America and northern South America (Lefebvre et al. 1992, 1994; Petit et al. 1995; Lefebvre and Poulin 1996). It also winters in swamps and wet woodlands and occasionally in drier woodlands (including pine forest), mainly below an elevation of 1300 m (Bent 1953; Arendt 1992; Curson 1994). The habitat preferences (e.g. structure, species composition, spatial characteristics, stand age, moisture regimes) of wintering Prothonotary Warblers have not been quantitatively described, although black mangrove (Avicennia germinans) forest is a primary habitat type in Venezuela and Panama (Lefebvre et al. 1994; Lefebvre and Poulin 1996).

1.5 Threats

The following is a list and description of the known and perceived threats that the Prothonotary Warbler faces. Threats to the survival of the species* or its habitat** are presented in order of significance:

i) Loss/degradation of breeding habitat**

The decline of Prothonotary Warbler populations in the United States is attributable to losses in wetland habitat (Petit 1999). In the contiguous United States, only 10% of the original bottomland forest habitat remains (Dickson et al. 1995). In the southeastern United States, forested wetlands are being lost at a very high rate (Winger 1986; Hefner et al. 1994). Losses have been particularly high in coastal Louisiana and the Carolinas (U.S. Department of the Interior 1994), which are two of the Prothonotary Warbler’s core breeding regions. A similar pattern of habitat loss has occurred in the Prothonotary Warbler breeding range in Canada, where nearly all deciduous swamp forests have been drained to varying degrees or cut over. In southern Ontario, Snell (1987) estimated that wetlands had been reduced by about 1.5 million hectares (61%) from the time of European settlement to 1982. Between 1967 and 1982, wetlands in southern Ontario were reduced by about 39 000 ha, mostly due to agricultural activities (Snell 1987). Since 86% of the wetlands remaining in southern Ontario were forested swamps (Snell 1987), most of the loss is assumed to have involved this type of habitat. While there is no updated information on the extent of wetland loss in southern Ontario since the 1980s, sites continue to be drained (e.g. by ongoing activity of municipal drains).

In Canada, drainage of swamp forests, whether through ditching, agricultural tiling, municipal drains, or irrigation, depletes the water table and removes standing water. This is one of the most significant, widespread, and ongoing threats facing Prothonotary Warblers in this country.

Development activities can also contribute to the loss of habitat. One regularly occupied nesting site (Turkey Point) was destroyed when it was developed into a marina/trailer park (McCracken 1981). Because some jurisdictions in southern Ontario do not have tree-cutting bylaws, some forms of development are also likely to involve removal of large swaths of forest and infilling of swamps. For example, attempts were recently made to develop a large swamp forest in Essex County (“Marshfield Woods”), which was believed to support one or more Prothonotary Warblers, into a golf course (McCracken and Mackenzie 2003). In addition, residential/estate development adjacent to swamp forests is likely to artificially increase local populations of nest predators (e.g. raccoons [Procyon lotor]) and/or competitors (e.g. House Wrens [Troglodytes aedon]).

Logging disturbances that take place in important habitat create forest openings and edge habitat that can reduce the amount of open water cover in swamp forests through heightened evaporation. The increased light penetration can also result in rapid encroachment of invasive plants (e.g. common reed; European alder [Alnus glutinosa]). In addition, removal of standing dead timber (e.g. for firewood) results in loss of nesting cavities.

ii) Loss of wintering habitat**

Coastal mangrove forest in Latin America is highly threatened by deforestation for building supplies, charcoal production, and resort development (Terborgh 1989; Petit et al. 1995). Mangrove habitat is also under increasingly intense pressure from commercial shrimp farmers (e.g. Arendt 1992). Loss and degradation of wintering habitat are believed to have a strong effect on wintering Prothonotary Warblers (Lefebvre et al. 1994; McCracken 1998) and are likely contributing to the species’ decline continentally.

There is little information on the degree of year-to-year site fidelity to wintering sites, but what data exist (McNeil 1982; Faaborg and Arendt 1984; Lefebvre et al. 1994; Woodcock et al. 2004) suggest that the Prothonotary Warbler is quite site faithful. This attribute may increase the species’ sensitivity to habitat loss and disturbance (e.g. Holmes and Sherry 1992; Warkentin and Hernandez 1996).

iii) Threats that increase nest site competition and reduce breeding productivity*

Several alterations to habitat (e.g. loss or reduction of forest cover through logging, increased forest fragmentation) result in declines in breeding success of Prothonotary Warblers, due to increased levels of nest competitors, nest predators, and brood parasites.

In regions where it is common, the House Wren is the most serious (and damaging) competitor for cavity nest sites (Walkinshaw 1941, 1953; Bent 1953; Best and Fondrk 1995; Flaspohler 1996; Knutson and Klaas 1997). Wrens prefer forest edges and fragmented forests and are a major problem at several sites that are important to Prothonotary Warblers in Canada (McCracken and Wood 2005). Not only do wrens directly attack (“vandalize”) the eggs and young of Prothonotary Warblers, they also build many “dummy” nests, often filling every available cavity in their territory with sticks. This directly displaces nesting Prothonotary Warblers and indirectly reduces cavity availability, thereby further increasing competition for nest sites. Moreover, the sticks are liable to persist in the cavities for many years, effectively rendering them unsuitable for all other species but wrens. Lastly, House Wrens produce at least two broods per year, which means that their impacts extend throughout the duration of the Prothonotary Warbler’s nesting season.

In more open areas, Tree Swallows (Tachycineta bicolor) can also be serious competitors for nest sites (McCracken 1981; Best and Fondrk 1995). However, because Tree Swallows nest relatively early and are typically single-brooded, competition for nest sites begins to decline at the end of June, and they are not considered as serious a competitor as House Wrens. Moreover, unlike wrens, swallows do not aggressively destroy the eggs of competitors, nor do they usurp other cavities by building “dummy” nests.

Some protection from potential nest predators is probably conferred because Prothonotary Warbler nests are situated in cavities and are usually over open water (e.g. Nice 1957). Including artificial nest sites, nest predation rates reported in the literature are highly variable: 2.6–53.3% in Tennessee (Petit et al. 1987; Petit 1989, 1991; Petit and Petit 1996); 15.5% in Virginia (Blem and Blem 1992); 27.6% in Wisconsin (Flaspohler 1996); 41% in Tennessee/Michigan (Walkinshaw 1941); and 22% in Ontario (J.D. McCracken, unpubl. data).

Loss of Prothonotary Warbler young and eggs is attributed to snakes, raccoons, mice (Peromyscus spp.), weasels (Mustela spp.), and squirrels (e.g. Glaucomys spp.) (Walkinshaw 1938; Bent 1953; Guillory 1987; Petit 1989; Blem and Blem 1992; Flaspohler 1996; Petit and Petit 1996). Walkinshaw (1941) largely blamed House Wrens for the poor nesting success of Prothonotary Warblers in Michigan, noting that wrens were absent from the warbler’s breeding habitat in Tennessee, where Prothonotary Warbler nest success was much greater. Flaspohler (1996) and Knutson and Klaas (1997) likewise suspected that House Wrens played a major role in nest failure in their Wisconsin studies, again in regions where House Wrens were common. Wrens were also regarded as a problem in one Ohio study (Best and Fondrk 1995). In Canada, House Wrens figure prominently in the destruction of Prothonotary Warbler nests in sites that do not have extensive forest and canopy cover (McCracken 2004).

Predation of nests by raccoons in natural cavities (or in unprotected boxes that are affixed to trees rather than on slippery steel poles) also figures prominently, especially in human-modified landscapes. It is generally believed that birds (including Prothonotary Warblers) using nest boxes benefit from reduced rates of predation (e.g. Nilsson 1986; Moller 1989; Blem et al. 1999; Mitrus 2003; McCracken and Wood 2005) compared with birds using nests in natural cavities, because of protection afforded by overhanging rooftops, the controlled diameter of entrance holes, and the use of metal poles and protective guards.

Brood parasitism from Brown-headed Cowbirds (Molothrus ater) may limit population size and contribute to population declines by reducing the productivity of Prothonotary Warblers (McCracken 1981; Flaspohler 1996). Many Prothonotary Warbler breeding studies are based on artificial nest structures, which usually confer protection against parasitism (Walkinshaw 1991; Best and Fondrk 1995; Flaspohler 1996), because nest hole diameter is smaller than in natural situations. An exception was Twedt and Henne-Kerr (2001), who recorded a surprisingly high level of parasitism (45%) in their nest boxes, although they did not report nest hole diameter. In any case, for Prothonotary Warbler natural cavity nests, cowbird parasitism rates are surprisingly high: 21% in Tennessee (Petit 1989, 1991); 25.7% in Iowa (based upon data in Bent 1953); 26.9% in Wisconsin (Flaspohler 1996); and 27.1% in Ontario (Peck and James 1998). It is likely that land use patterns and regional forest fragmentation determine the regional abundance of cowbirds (Flaspohler 1996), perhaps explaining the extremely low incidence of parasitism (0.01%) found in Virginia (cited in Flaspohler 1996). Distance from the historical heartland of the cowbird’s range may also be a factor (Hoover and Brittingham 1993).

iv) Invasive forest insects**

Forest insect infestations have the potential to kill large numbers of trees. While this could benefit Prothonotary Warblers in the short term through the creation of more nesting habitat (in the form of dead stubs), the long-term impact is expected to be severe if the affected trees make up a large proportion of the canopy. Anything that significantly opens the tree canopy is likely to result in significant degradation in habitat quality, whether it is through encroachment of invasive plants or increased numbers of wrens and cowbirds.

The emerald ash borer (Agrilus planipennis) is of increasing concern in southern Ontario, since ash is a frequent subdominant tree in swamp forests here. In the slough forests at Rondeau Provincial Park, a recent study found that ash makes up 47% of the tree cover (McCracken et al. 2006). In addition to direct loss of tree cover by the insect itself, aggressive attempts to curb or contain the invasion of the emerald ash borer can result in the loss of substantial tree cover. For example, across Essex County, many of the ash have already succumbed to the insect, while there are programs planned or in place to remove ash from large areas of the Chatham-Kent region (S. Dobbyn, pers. obs.).

The Asian longhorned beetle (Anoplophora glabripennis) is also an emerging issue of great concern, depending upon its ability to spread beyond its present area of containment and its affinity for silver maple.

v) Invasive plants**

Two invasive species of plants -- the common reed and European black alder -- can significantly degrade Prothonotary Warbler breeding habitat, particularly when water levels are low or canopy cover is reduced.

Within the last decade at Rondeau Provincial Park, the common reed has expanded dramatically through many of the slough forests, especially in the larger and more open sloughs and in areas where canopy closure has been reduced (due to windthrow). Because the Prothonotary Warbler requires expanses of open water, this invasive emergent effectively fills in the open pools of water, rendering the site unsuitable.

Likewise, European black alder is a highly invasive shrub that can also significantly degrade Prothonotary Warbler nesting habitat in open swamp forest conditions. It is already abundant in at least one primary nesting location (Hahn Woods) and is a major problem at several sites undergoing restoration in Norfolk County.

vi) Catastrophic weather events*

The intensity and frequency of storms (including hurricanes) on both the wintering and breeding grounds are anticipated to increase as a result of climate change. Owing to the Prothonotary Warbler’s clumped and restricted distribution in Canada, disasters associated with catastrophic weather events along the north shore of Lake Erie pose a serious threat to this species. Ensuring that the population is spread out across a number of geographically separated breeding sites will buffer Canadian populations against local disasters.

vii) Toxic chemicals and other pollution*

On the Prothonotary Warbler’s breeding grounds in Canada, mosquito control programs (e.g. in response to West Nile virus) have the potential to impact Prothonotary Warblers, particularly if adulticides are used in occupied habitats, either through direct poisoning of the birds or through reduction in food supply.

Detrimental effects from insecticides are of greatest concern on the Latin American wintering grounds, where DDT is still used widely for malaria control (Arendt 1992). As well, various kinds of water pollution associated with shrimp aquaculture seriously jeopardize mangrove forest (Olson et al. 1996). A major oil spill could also seriously damage wintering habitat (Arendt 1992).

1.6 Actions Already Completed or Under Way

The following is a brief synopsis of recovery activities that have been undertaken on behalf of Prothonotary Warblers in Canada since 1997:

  • A multi-agency recovery team was created in 1997, and a draft recovery plan was produced in 1998. Most of the current recovery team members have been involved since the team’s inception.
  • A nest box program has been in operation in southwestern Ontario since 1998. The program now includes nearly 300 nest boxes distributed across nearly 20 sites. Side projects have tested various experimental nest box designs and configurations with regard to their effectiveness for dissuading occupancy by House Wrens.
  • Population and nest productivity surveys have been conducted annually since 1998.
  • A colour banding program (mostly focused on adults) has been conducted annually in Ontario since 1998 in order to study demographics and site fidelity.
  • Detailed quantitative habitat assessments were conducted at two of the most important breeding sites in 2005. Less detailed habitat assessments were conducted at all occupied sites in 1998.
  • A population viability analysis and a landscape-scale habitat modelling analysis have been conducted.
  • About 80 potential candidate sites have been assessed and scored for their restoration potential. Working with a number of partner agencies and organizations, a variety of habitat restoration activities have been conducted at about 10 of the most promising sites to date, with more in the planning stages.
  • The recovery team provided input to the Ontario Ministry of Natural Resources, leading to the designation of the species under Ontario’s Endangered Species Act.
  • Communications have been initiated with recovery practitioners at two sites in Ohio.
  • Field investigations (involving intensive banding and habitat assessments) have been conducted at several mangrove sites in Costa Rica for four full winters (December through March). Information related to winter site fidelity and demographics is being collected. In addition, a study was conducted on isotopes from a sample of tail feathers from the winter study sites to see whether the local wintering population originated from across the species’ breeding range or had a more restricted geographic origin.
  • A web page was launched by the recovery team in 1999, which led to the production of an information pamphlet on the species. Over 10 000 pamphlets have been distributed, and the web page is still one of the top-visited Internet pages for people looking for reference information on Prothonotary Warblers.
  • Detailed annual reports on all recovery activities have been produced for project partners since 1998.

1.7 Knowledge Gaps

In addition to information gaps related to the identification of critical habitat (Section 2.5), there is currently inadequate information available on:

  • effective techniques to control common reed and European black alder;
  • effective techniques to reduce impacts associated with House Wrens;
  • the potential impact of forest insect infestations (emerald ash borer and Asian longhorned beetle) on the quality of critical habitat;
  • the types and amounts of logging activities that Prothonotary Warblers may tolerate in their habitat before they abandon a site;
  • sources of the birds that immigrate into Ontario from the United States; and
  • wintering habitat needs in Latin America, including information on wintering site fidelity.