A Survey of Rusty Blackbird Populations in Northeastern Vermont

Research into habitat, distribution and breeding biology

A Senior Applied Research Project by Caleb Fisher

SterlingCollege, 2007

Life History and Status of the Rusty Blackbird

The Rusty Blackbird, Euphagus carolinus, is the northernmost breeder of the Icteridae, or North American blackbirds. This species, dependent on forested wetlands in both the breeding and non-breeding seasons, winters in the southeastern United States and breeds in boreal areas of North America. Unlike most other Icterids, whose populations remain healthy, the Rusty Blackbird has experienced massive population declines in the past century. While many theories exist for the causes of decline, there is an evident lack of both data and monitoring programs to support any of these theories and to provide a fully accurate assessment of their current population. The lack of attention given to Rusty Blackbirds has caused their decline to be largely overlooked by bird researchers, conservationists and the general public (Greenberg and Droege, 1999).

Physiological Characteristics

Rusty Blackbirds, named after their non-breeding plumage, are recognized in the fall and winter by overall black plumage and rusty brown coloring on the crown, nape, back and tertial edges of the males with a lighter brown over the eyes, cheeks, throat and breast (Avery, 1995). Females are similar in appearance but have lighter, buff-brown edgings on their eyes, cheeks, throat, sides and breast, as well as a pale buff line above the eyes. In the breeding season, males are uniformly black with a blue-green to green gloss while females are slate gray, darker above, with a blue-green gloss. Immature birds are overall more brown appearance and have brown irises until the fall. All mature Rusty Blackbirds have a yellow iris and a bill that is shorter than the head. The two species most easily confused with Rusty Blackbirds are the Brewer’s Blackbird (Euphagus cyanocephulus) and the Common Grackle (Quiscalus quiscula) (Avery, 1995).

Taxonomy

Rusty Blackbirds belong to the Passeriformes order and the Icteridae, or the New World blackbird, family. This family contains 94 species and is thought to have evolved from a finch-like ancestor in tropical South America (Orians, 1985). The closest relative of the Rusty Blackbird is the Brewer’s Blackbird (Euphagus cyanocephalus) with Euphagus appearing most closely allied with the grackles (Quiscalus) (Irwin, 1994, Hannah, 2004). Rusty Blackbirds are divided into two subspecies: Euphagus carolinus carolinus, distributed over most of the species range and the darker E. c. nigrans, breeding in Nova Scotia, Newfoundland, MagdelanIsland and eastern New Brunswick (Avery, 1995, Hannah, 2004).

Distribution

Rusty Blackbirds, as with all members of the Icteridae, are a New World species. As the most northern member of the group, they breed across the entire North American boreal forest from the west coast of Alaska to the east coast of Canada and Newfoundland. They breed as far north as the tree line and south through central British Columbia, Alberta, Saskatchewan and Manitoba, to southern Ontario and the northern Great Lakes, southern Quebec and northern New York and New England (Avery, 1995). Historically, they were most abundant in the eastern boreal forest (Greenberg and Droege, 1999). Their primary wintering range is the southeastern United States, from eastern Texas, Oklahoma, Kansas and Nebraska, east to the Atlantic and Gulf coasts, south to central Florida and north to southern Massachusetts. Their peak abundance stretches in a belt from central Oklahoma to central North Carolina. (Avery, 1995, Hannah, 2005).

Migration

Annual northern migrations take place from March to May and southern migrations from September to

November. They migrate diurnally and most often in flocks. These can be mixed species flocks with other blackbirds, but often they are single-species (Avery, 1995). Flocks containing thousands of individuals were often recorded in the early 20th century (Greenberg and Droege, 1999).

Habitat

The Rusty Blackbird’s dependence on forested wetlands makes them one of the most specialized of the North American blackbirds (Avery, 1995, Greenberg and Droege, 1999). In the breeding season, they are found in wet coniferous and mixed forests, frequently in fens, bogs, alder-willow thickets, beaver ponds, muskeg and the edges of lakes and streams. During migration they are common in open woodland, pasture, cultivated fields and wetland edges (Avery, 1995, Hannah, 2005). In the winter, they are dependent on wet woodlands, swamps and pond edges and usually are not associated in large numbers with the enormous, mixed species roosts of other blackbirds wintering in the southeast U.S. (Avery, 1995, Dolbeer, Woronecki, Stickley, White, 1978).

Breeding

Rusty Blackbirds are loosely colonial, often migrating in large flocks, but nesting in isolated, monogamous pairs (Avery, 1995). Breeding densities are low throughout their range (Hannah, 2004) and nests have never been recorded closer than 0.4 miles (Avery, 1995). In Vermont, nest-building is known to begin in late April, with clutches starting in the first or second week of May (Ellison, 1990). Usually 4-6 eggs are laid (Hannah, 2004) and are incubated solely by the female. Incubation lasts for about 14 days and chick development is rapid (Avery, 1995), with records of flight 13 days post-hatch. Fledglings have been recorded as early as the 12th of June in Vermont (Ellison, 1990). One brood is raised per breeding season; however they will attempt nests and clutches several times if initial attempts are unsuccessful (Avery, 1995).

The large, bulky nests are constructed solely by the female (Avery, 1995). The outer frame is made of twigs, dried grasses and Usnea lichen (Avery, 1995, Nichols, 1985, Peterson, 1988) and lined inside with 5-10 cm thick walls of wet, rotting vegetation. This is then lined with plant fibers and dried grasses with the innermost layer made of fine green grasses. Completed nests are typically 14-20 cm across and 8-9 cm deep. Nests are almost always located near water and are .5-6m above the ground. Surrounding vegetation is dense and nests are often located against tree trunks or among thick layers of small branches. The nests are most often placed in a spruce, fir, tamarack, willow or alder (Avery, 1995). In Vermont, spruce and balsam fir are most common, but Speckled Alder (Alnus rugosa), Willow (Salix spp.) and Sweet Gale (Myrica gale) are also used (Nichols, 1985). Although nesting sites are returned to, nests are not reused in subsequent years, but may be used by other species like the Solitary Sandpiper (Tringa solitaria) (Avery, 1995, Granlund, 1991).

Diet

Rusty Blackbirds are opportunistic feeders throughout the year; however, during the breeding season they are much more dependent on aquatic invertebrates and other high-nutrient animal foods (Avery, 1995, Hannah, 2004). Their most common foods include insects and larvae, grain crops, seeds, snails and crustaceans as well as fruits, fish and salamanders. They have also been known to prey on other bird species during times of harsh weather and food shortage (Avery, 1995, Hannah, 2004). They are most commonly seen foraging on the ground, especially near wetland edges, and in agricultural fields during migration (Avery, 1995). Their long-narrow bill is well-adapted for an insectivorous diet, allowing them to loosen soil, dig through debris and wade and plunge their heads into water after aquatic invertebrates (Avery, 1995, Orians, 1985).

Vocalization

Both male and female Rusty Blackbirds sing while on their breeding grounds (Avery, 1995). The male has two songs that are often described as resembling a rusty hinge; paraphrased as “kush-a-lee” and “ksh-lay”,and also produce a loud “chack” note (Peterson, 2002). Females sing while on the nest in response to the males, but their calls have not been described (Avery, 1995).

Current Status

Often described as abundant in the past, Rusty Blackbird populations appear to be in a major decline that has been occurring for at least the past century. While no monitoring programs exist for Rusty Blackbirds specifically, surveys like the Quebec Checklist Program, the Christmas Bird Count and the Breeding Bird Survey, as well as various sources of ornithological literature indicate an approximate decline of 90% in the past three decades and steady declines over the past century (Droege and Greenberg, 1999). The most significant declines have occurred in the eastern boreal forest and the Maritime Provinces of Canada (Hannah, 2004).

While many blackbird species have benefited from the expansion of agricultural and urban areas, Rusty Blackbird populations have suffered due to their dependence on wooded wetlands and aquatic invertebrates (Greenberg and Droege, 1999). It is estimated that 75% of the once nearly contiguous bottomland forests of the lower MississippiValley have been converted to agriculture, with the remaining patches of forests being highly fragmented (Loesch and Twedt, 1999). While this seems the most likely cause for declines, there is evidence suggesting that changes in breeding habitat may also be contributing. Species such as the Horned Grebe (Podiceps auritus) and Lesser Yellowlegs (Tringa flavipes), who also breed in boreal-type wetlands, are showing similar declines (Hannah, 2004). Also, the rate of habitat loss has not kept up with the rate of declines and population densities are falling in protected habitats as well (Droege and Greenberg, 1999).

There are other hypotheses for factors that may at least have contributed to Rusty Blackbird declines. Acidification of wetlands due to acid rain has been shown to affect calcium bearing mollusk and insect species (Schindler, 1988). Calcium is essential for bone and eggshell formation and a decrease in these important food sources may affect populations. Blackbird control programs in agricultural areas of the southeastern United States, involving chemical spraying of the immense, multi-species roosts wintering there, is a source of Rusty Blackbird mortality (Greenberg and Droege, 1999). However, in a study done in the 1970’s documenting species mortality in these roosts, Rusty Blackbirds represented less than one percent of the total number of birds killed (Dolbeer, Stickley, White and Woronecki, 1978). The other roosting species have shown much less, if any, decline (Greenberg and Droege, 1999). Competition from other bird species on breeding grounds, primarily the Red-Winged Blackbird and the Common Grackle, may also be contributing to reduced Rusty Blackbird numbers (Erskine, 1992, Avery, 1995). These birds are more aggressive and competitive and have shown dominant behavior over Rusty Blackbirds (Ellison, 1990, Hannah, 2004). Due to the opening of forests, Grackles and Red-Wings have gained access to wetland habitat that they historically would not have inhabited (Wilcove and Whitcomb, 1983, Erskine, 1992, Avery 1995). Parasitism by the Brown-Headed Cowbird is typically not a concern because Rusty Blackbirds tend to breed north of their range and in different habitat types (Avery, 1995).

What is known about Rusty Blackbirds is they are in a decline that, according to surveys and literature, is among the most significant of any North American species. Unfortunately, without any monitoring programs it is difficult to notice long-term population changes and understand the true reasons for their occurrence. Rusty Blackbird populations are listed as “demonstratably secure” in the United States

National Heritage Status Rank, Canada National Heritage Status Rank and Global Heritage Status Rank, they are not included on the National Audubon Society’s Blue List and are listed on the American Bird Conservancy’s Green List as “moderately abundant, declining and with a high degree of threat” (Hannah, 2004). There is no management of the species anywhere within its range (Avery, 1995, Greenberg and Droege, 1997, Hannah, 2004). Their remote breeding habitats, low population densities, broad distribution and relatively discreet habits do not bring them into the forefront of most research and conservation efforts. However, with Audubon’s Christmas Bird Count and the USGS Breeding Bird Survey both showing yearly declines between 5 and 10 percent and similar population trend lines showing a drastic population crash over the past forty years (Niven and Sauer, 2004), it is evident that Rusty Blackbirds need more attention than they are currently receiving. Substantial research is needed on their life history, breeding biology and population status (Greenberg and Droege, 1999). Without sufficient data that is current, concrete and accurate, the Rusty Blackbird is not likely to receive the conservation measures it may deserve.

Rusty Blackbird ResearchProposal

Question

Through the collection of information on Rusty Blackbird breeding biology and distribution in northeastern Vermont, what can be inferred about the causes of the current decline of this species and how can these results contribute to future conservation efforts?

Objective

This project aims to assess the distribution and abundance of Rusty Blackbirds in northeastern Vermont and add to the limited records of breeding biology information for this species. The following questions will be addressed to establish this data:

  • Where and how are populations of Rusty Blackbirds distributed in northeastern

Vermont?

  • What is the breeding status of these populations?
  • How successful are breeding attempts in northeastern Vermont?
  • What types of wetlands are preferred by breeding Rusty Blackbirds in northeastern

Vermont?

  • What does the collection of vegetation and water quality data around nest locations

tell about breeding habitat preference?

  • What can be inferred about the Rusty Blackbird’s food preferences, home range,

behavior and interaction with other species through observation in the field?

Vermont Summary

Very little is known about Rusty Blackbird breeding biology. Until 2006 there had only been two studies done on the species in their breeding grounds. The first of these studies occurred in 1920 and measured re-nesting attempts after nest destruction. The only other study, done by Walter Ellison, occurred in Vermont in 1990. This study surveyed Rusty Blackbird locations found during the Vermont Breeding Bird Atlas and has contributed the majority of breeding observations of the species.

Last year marked the beginning of a concerted effort to gather field information on Rusty Blackbirds. This year, 2007, will host the most extensive studies to date and build a framework of information for future study. Breeding ground research in 2007 will occur in the northeastern United States, Alaska and Alberta, Canada.

The Vermont Breeding Bird Atlases provide an overall sense of the distribution of Rusty Blackbirds in Vermont. The first atlas, conducted from 1979 to 1983, found Rusty Blackbirds at 46 locations with 14 cases of confirmed breeding. The second atlas project began in 2003 and will be completed this year. So far, there have been 26 sightings with 13 cases of confirmed breeding.

The atlases indicate two centers of Rusty Blackbird population in the state; in the southern Green Mountains and in the highlands of the NortheastKingdom. Only 8 sites, 4 with confirmed breeding, have recorded Rusty Blackbirds in both atlases. While their disappearance is occurring in both regions, the south appears more severe as most new occurrences are in the northeast portion of the state.

Conducting Surveys

This project is focused on Orleans, Caledonia and Essex counties located in northeastern Vermont. Data from the Vermont Breeding Bird Atlas is indicating this to be the primary breeding range of Rusty Blackbirds in Vermont. In 2007, field surveys in the northeastern U.S. will be taking place in Maine, New Hampshire, Vermont and New York. There is effort to standardize the research methods being used for all northeastern surveys. This project will follow protocols created by the Maine Department of Inland Fisheries and Wildlife (see Appendix A). All surveys will take place between May 10th and June 18th, 2007.

A typical survey will involve accessing a point that provides an unobstructed view of as much of the wetland as possible. A five minute period of passive observation will be conducted from this point, followed by a recording of all available information for the data sheet. A broadcast of Rusty Blackbird calls and a three minute observation period will follow. A large wetland may require two surveys. One datasheet will still be used for these wetlands and the coordinates of both broadcast sites will be recorded. If there is no response then the survey is over upon completion of the data sheet. Rusty Blackbird response to the callback necessitates as much observation of the individual as possible, with the recording of all notable behaviors and determination of breeding status.

Site Selection

Survey sites need to be selected randomly so as to gain a better sense of Rusty Blackbird distribution and preference of wetland type. The project area will be divided using 7.5 minute USGS topographic maps. Two wetlands will be randomly selected for every map that is more than 50% within the project area. One site will be selected for maps less than 50% in the project area.