2010 NORTHEASTERN NATURALIST 17(4):639–646 A Loose Colony of Rusty Blackbirds Nesting in Northern Maine Luke L. Powell1,2,*, Thomas P. Hodgman3, William E. Glanz4, James D. Osenton5, and David M. Ellis5 Abstract - Euphagus carolinus (Rusty Blackbird) has suffered a steep population decline over the past 40 years, yet we still understand little of the basic biology of the species, particularly its social organization. During the spring of 2007, we located a loose colony of Rusty Blackbirds breeding in Piscataquis County, ME. The core colony consisted of six nests within 6.9 ha. These nests were located within a 70-ha clearcut dominated by regenerating Picea rubens (Red Spruce), P. mariana (Black Spruce), and Abies balsamea (Balsam Fir). Within 1500 m of the core colony, we located two “satellite” nests in young forests regenerating from heavy partial harvests. We observed mobbing behavior by multiple individuals from different pairs, suggesting that coloniality in this species may be an antipredator strategy. Introduction The steep and range-wide decline of Euphagus carolinus (Statius Muller) (Rusty Blackbird) has been documented now for over a decade (≈ 90% since 1966; Greenberg and Droege 1999; Greenberg et al., in press; Niven et al. 2004). Yet, there remains surprisingly few studies of the breeding biology of the species. Most of the available information is from anecdotal accounts across North America’s boreal forest, where the species breeds in wetlands variously described as swampy woodlands, fens, bogs, muskegs, damp alder swales, and Castor canadensis (Kuhl.) (Beaver)-modified wetlands (Avery 1995, Ellison 1990, Erskine 1992, Kennard 1920, Laughlin and Kibbe 1985, Peterson 1988, Richards 1995). In northern and western Maine, Rusty Blackbirds reach the southeastern limit of their breeding range (T.P. Hodgman, unpubl. data). Breeding adults nest in dense patches of small conifers (Avery 1995; Matsuoka et al., in press; Powell et al., in press[a]) and feed by wading in or near shallow water in search of aquatic invertebrates (Ellison 1990, Martin et al. 1951). While most accounts describe the species as a solitary breeder (Avery 1995, Flood 1978), observations in Newfoundland (Peters and Burleigh 1951), Labrador (Todd 1963), and Alaska (Gabrielson and Lincoln 1959) suggest that pairs can congregate into small breeding colonies. Orians (1985) described Rusty Blackbirds as “loosely colonial”; 1School of Biology and Ecology, University of Maine, Orono, ME 04469. 2Current address - School of Renewable Natural Resources, Louisiana State University, Baton Rouge, LA, 70803. 3Maine Department of Inland Fisheries and Wildlife, Bangor, ME 04401. 4School of Biology and Ecology, University of Maine, Orono, ME 04469. 5Department of Wildlife Ecology, University of Maine, Orono, ME 04469. *Corresponding author - LPowel9@LSU.edu. 640 Northeastern Naturalist Vol. 17, No. 4 however, active nests have not been found closer than 400 m of one another in New England (Avery 1995, Kennard 1920). Increased nesting density can reduce nest predation for other colonial marsh-nesting blackbirds (Picman et al. 1988, Ritschel 1985, Yasukawa et al. 1992); thus, understanding colonies and colony formation could be useful in the conservation of declining Rusty Blackbirds. Here we provide the first reported “loose colony” of Rusty Blackbirds in New England and speculate on the environmental conditions that may contribute to colony formation. Methods Forests in northern Maine are managed for timber harvests consisting mostly of partial cuts (>95% of harvests) along with a much lesser amount of clearcuts (less than 5%; Maine Forest Service 1999, McWilliams et al. 2005). Large stands were harvested during and following a massive outbreak of Choristoneura fumiferana (Clemens) (Spruce Budworm) in the late 1970s and are now regenerating into densely stocked stands of young conifers. We traveled hundreds of kilometers of forest roads in Maine and Vermont in search of nesting pairs of Rusty Blackbirds from 10 May–25 June in 2006, 2007, and 2008. This effort was part of a larger study of the distribution and breeding ecology of the species(see Powell 2008). In total, we surveyed for Rusty Blackbirds at 561 wetlands within the breeding range of the species and located 43 nests over the three years (see Powell et al., in press a). Upon finding a wetland occupied by Rusty Blackbirds, we searched for nests based on the recommendations of Martin and Geupel (1993). Using binoculars and scanning these wetlands for adult Rusty Blackbirds, we followed them back to their nests. Males vocalizing with their mouths shut were often preparing to deliver food to young or an incubating female (L.L. Powell, pers. observ.; Hoffman and Hoffman 1982; Matsuoka et al., in press). After hatching, nests became easier to locate, as both parents regularly returned to the nests to provision their young with food. As part of a concurrent study of home range (Powell et al., in press [b]), we captured, banded, and radio-tagged eight members of this colony. Also for concurrent studies, we visited the colony multiple times to estimate detectability and site fidelity (Powell 2008; Powell et al., in press [a]). We used Hawth’s Tools for ArcGIS 9.2 (Beyer 2004, ESRI 2006) to estimate distances between nests and to calculate the minimum convex polygon (MCP) encompassing nests. We used a digital copy of the National Wetlands Inventory (Cowardin et al. 1979) to characterize wetland cover. Results On 26 May 2007, we located several pairs of Rusty Blackbirds in a regenerating 13-year-old, 70-ha clearcut in Township 6, Range 15 (i.e., T6 R15 WELS) of Piscataquis County, ME (Fig. 1). A well-maintained dirt road bisected this even-aged stand, which was dominated by densely regenerating 2010 L.L. Powell, T.P. Hodgman, W.E. Glanz, J.D. Osenton, and D.M. Ellis 641 Picea rubens Sarg. (Red Spruce), P. mariana (P. Mill.) B.S.P. (Black Spruce), and Abies balsamea L. (Balsam Fir), and perforated by an occasional mature Pinus strobus L. (White Pine; approx. 2 trees per ha). This stand was part of a habitat mosaic that included several open patches of wet Sphagnum spp. and one 0.5-ha patch of scrub-shrub wetland (Cowardin et al. 1979). We found six nests in the regenerating conifers surrounding the scrub-shrub wetland, hereafter referred to as the “core colony” (Fig. 1). This wetland was shallow (water primarily less than 10 cm deep), included sedges (Carex spp.) and other graminoids, and was surrounded by Alnus incana L. (Speckled Alder). We also found two “satellite” nests situated 869 and 1481 m from the core colony (Fig. 1). The former was constructed 95 m from a 1.3-ha forested wetland dominated by standing dead Thuja occidentalis L. (Northern White Cedar); the latter was located 32 m from a small unconsolidated bottom wetland (less than 0.2 ha) surrounded by sedges and both regenerating Figure 1. Eight Rusty Blackbird nests forming a “loose colony” in northern Maine, 2007. The six nests in the bottom center represent the “core colony”, and the two distant nests in the northeast corner represent “satellite nests”. Wetlands classification follows the National Wetland Inventory (Cowardin et al. 1979), and white space represents forested upland. 642 Northeastern Naturalist Vol. 17, No. 4 and mature spruce and Balsam Fir. These satellite nests were constructed east and northeast of the core colony on hills that were partially harvested within the past 13 years and were regenerating to Rubus sp. (raspberry). The six nests in the core colony were located within a MCP of 6.9 ha, and all eight nests were located within a MCP of 36.9 ha. Nests in the core colony were 283 m ± 33 SE apart on average (range = 67−531). All eight nests were 761 m ± 112 SE apart on average (range = 67−1736). In 2007, we captured and color-banded 8 individuals: 6 in the core colony and 2 at the closest satellite nest (see Powell 2008). We observed pairs from both core colony and satellite nests foraging at the wetlands adjacent to their respective nests as well as in nearby wet depressions along roadsides formed by the removal of tree stumps. There were three occasions on which we observed males in the core colony aggressively chasing each other. We subsequently revisited the area on 27 May and 17 June 2008, but did not observe any Rusty Blackbirds in the area where the core colony was located in 2007. We did, however, find four adult Rusty Blackbirds in 2008 breeding adjacent to each of the satellite wetlands occupied in 2007, although none of these adults were color banded. Discussion In 2007, we found six active Rusty Blackbird nests clustered around a single 0.5-ha wetland, providing the first evidence of colonial nesting by this species in New England. Though Rusty Blackbirds usually nest solitarily (Avery 1995), there are reports of colonies in Newfoundland (Peters and Burleigh 1951), Labrador (Todd 1963), and Alaska (Gabrielson and Lincoln 1959). The two previous studies of Rusty Blackbirds in New England (Kennard [1920]: 16 nests, Ellison [1990]: 6 nests), however, report no evidence of coloniality, with Kennard (1920) specifying that he never saw more than one pair in a given area per season. Colonial nesting in New England is indeed rare; even with 561 wetlands surveyed and 43 Rusty Blackbird nests found over three breeding seasons (Powell 2008; Powell et al., in press [a]), we only located a single colony in 2007, and it did not return to the site in 2008. Based on observations at only one colony, we can merely speculate on the reasons for colony formation. Lack (1968) and Simpson et al. (1987) suggested that protection from predators is the primary reason that birds breed colonially, and our observations of Rusty Blackbirds appear to support this. For instance, on two occasions at the northern Maine colony, individuals from several pairs (as many as five males at a time) cooperatively mobbed our field crew near active nests. Similarly, Rusty Blackbirds from multiple breeding pairs have mobbed field crews that were checking nests at a site in New England (C.M. Fisher, Sterling College, Craftsbury Common, VT, pers. comm.) and several sites in boreal and coastal Alaska (Matsuoka et al., in press). Cooperative defense among colonial Rusty Blackbirds may deter potential predators from nests and fledglings more effectively (Greenberg et al., in press)—and with less risk to the individual. Such cooperative defense 2010 L.L. Powell, T.P. Hodgman, W.E. Glanz, J.D. Osenton, and D.M. Ellis 643 has been found in colonies of Xanthocephalus xanthocephalus (Bonaparte) (Yellow-headed Blackbirds; Picman et al. 2002), and likely deters potential predators from Agelaius phoeniceus (L.) (Red-winged Blackbird) nests (Picman et al. 1988). Powell (2008) found that daily nest survival of the birds in this colony was 0.950 ± 0.025 SE (22.4% success, n = 7), while daily noncolonial nest survival was considerably greater at 0.986 ± 0.007 SE (66.2% success, n = 25). However, timber management history around wetlands had a much greater influence on nest survival than did social structure. In other words, nests in this colony likely failed not because of the presence of the colony itself, but because the colony was located in a regenerating clear-cut that attracted nest predators (Powell et al., in press [a]). Multiple colonies under various management regimes must be studied to disentangle the effects of timber management and sociality on productivity. As an alternative to the hypothesis of defense against nest predators, Ellison (1990) cited Horn’s (1968) resource-based model for coloniality in the congeneric E. cyanocephalus (Wagler) (Brewer’s Blackbird), and speculated that colonial nesting may benefit Rusty Blackbirds when food is patchily distributed or ephemeral. Under such circumstances, individuals presumably would follow others to find food. Rusty Blackbirds that were part of this colony had home ranges that were 3 times larger than those of pairs that nested solitarily (Powell et al., in press [b]), which the authors speculate may be due to adults following one other to feed on unpredictable emergences of aquatic insects. Although this hypothesis appears logical and the general area surrounding the colony was a mosaic of shallow wetlands and upland, we collected no food-availability or foraging data with which to test it. Future studies of social organization in this species should evaluate whether individuals follow each other to ephemeral food sources (e.g., Ephemeroptera spp. [mayfly] hatches at nearby wetlands). Though Orians (1985) generally considered Rusty Blackbirds “loosely colonial” on their breeding grounds, the social organization in New England appears variable (Powell 2008). The colony formation of the species may be influenced by habitat availability or structure (Avery 1995), as variation in social structure tend to be adaptations to environmental conditions (Beckoff et al. 1984, Lott 1984, West-Eberhard 1989). Here, further research is needed to evaluate which environmental factors influence colony formation and if colonial nesting affects nest success or functions later to increase juvenile survival. Newfoundland may be a particularly well-suited location for this research, as Rusty Blackbirds are still relatively common in some areas (M. Elderkin, Nova Scotia Department of Natural Resources, Halifax, NS, Canada, pers. comm.), the species reportedly nests colonially there (Peters and Burleigh 1951, Todd 1963), and clearcutting is still common (Taylor and Krawchuk 2006). We may never be certain what caused such steep population declines in Rusty Blackbird populations, but by continuing to study the behavior and social organization of the species, we will be better equipped to make meaningful management decisions that improve the chance for recovery of the species. 644 Northeastern Naturalist Vol. 17, No. 4 Acknowledgments The Maine Warden Service, Pittston Farms, foresters with Seven Islands Land Co., and the good people at Russell Pond Bear Hunting Camp all provided critical logistical support. We thank Ryan Jones and Caitlin Holmberg for their tireless work as technicians during the 2007 field season. We thank Jana-Maria Hartmann, Jason D. Luscier, and Steve M. Matsuoka for providing constructive criticisms on earlier drafts of the manuscript. We performed this study in association with the Rusty Blackbird Working Group and received funding from the Maine Outdoor Heritage Fund, the Maine Endangered and Nongame Wildlife Fund (i.e., Loon License Plate), and the Maine Department of Inland Fisheries and Wildlife through Federal Aid in Wildlife Restoration. Literature Cited Avery, M.L. 1995. Rusty Blackbird (Euphagus carolinus). Pp. 1–16, In F.B. Gill and A. Poole (Eds.). Birds of North America, No. 200, Vol. 200. Academy of Natural Sciences, Philadelphia, and American Ornithologists' Union, Washington, DC. Beckoff, M., T.J. Daniels, and J.L. Gittleman. 1984. Life-history patterns and the comparative social ecology of carnivores. Annual review of ecology and systematics 15:191−232. Beyer, H.L. 2004. Hawth’s Analysis Tools for ArcGIS. Available online at http:// www.spatialecology.com/htools. Accessed 4 March 2009. Cowardin, L.M., V. Carter, F.C. Golet, and E.T. LaRoe. 1979. Classification of the Wetlands and Deepwater Habitats of the United States. US Fish and Wildlife Service, Washington DC. Ellison, W.G. 1990. The status and habitat of the Rusty Blackbird in Caledonia and Essex counties. Vermont Fish and Widlife Department, Woodstock, VT. Erskine, A.J. 1992. Atlas of Breeding Birds of the Maritime Provices. Nova Scotia Museum, Halifax, NS, Canada. ESRI. 2006. ArcGIS, version 9.2. Environmental Systems Research Institute, Redlands, CA. Flood, N. 1978. Rusty Blackbirds. Pp. 476−477, In M.D. Cadman, P.F.J. Eagles, and F.M. Helleiner (Eds.). Atlas of the Breeding Birds of Ontario. University of Waterloo Press, Waterloo, ON, Canada. Gabrielson, I.N., and F.C. Lincoln. 1959. The Birds of Alaska. The Stackpole Co., Harrisburg, PA. Greenberg, R., and S. Droege. 1999. On the decline of the Rusty Blackbird and the use of ornithological literature to document long-term population trends. Conservation Biology 13:553−559. Greenberg, R., D.W. Demarest, S.M. Matsuoka, C. Mettke-Hofmann, M.L. Avery, P.J. Blancher, D.C. Evers, P.B. Hamel, K.A. Hobson, J. Luscier, D.K. Niven, L.L. Powell, and D. Shaw. In press. Understanding declines in Rusty Blackbirds. Studies in Avian Biology. Hoffman, K., and M. Hoffman. 1982. Minnesota's first Rusty Blackbird nest. Loon 54:141−143. Horn, H.S. 1968. The adaptive significance of colonial nesting in the Brewer's Blackbird (Euphagus cyanocephalus). Ecology 49:682−694. Kennard, F.H. 1920. Notes on the breeding habits of the Rusty Blackbird in northern New England. Auk 37:412−422. 2010 L.L. Powell, T.P. Hodgman, W.E. Glanz, J.D. Osenton, and D.M. Ellis 645 Lack, D. 1968. Ecological Adaptations for Breeding in Birds. Methuen and Co., London, UK. Laughlin, S.B., and D.P. Kibbe. 1985. The Atlas of Breeding Birds of Vermont. University Press of New England, Hanover, NH. Lott, D.F. 1984. Intraspecific variation in the social systems of wild vertebrates. Behaviour 88:266−325. Maine Forest Service. 1999. State of the forest and recommendations for forest sustainability standards. Available online at http://www.state.me.us/doc/mfs/ sofjun12.PDF. Accessed 10 March 2000. Martin, A.C., H.S. Zim, and A.L. Nelson. 1951. American Wildlife and Plants. McGraw-Hill, New York, NY. Martin, T.E., and G.R. Geupel. 1993. Nest-monitoring plots: Methods for locating nests and monitoring nest success. Journal of Field Ornithology 64:507−519. Matsuoka, S.M., D. Shaw, P.H. Sinclair, J.A. Johnson, R.M. Corcoran, N.C. Dau, P.M. Meyers, and N.A. Rojek. In press. Nesting ecology of Rusty Blackbirds in Alaska, with reference to nest records from Canada. Condor. McWilliams, W.H., B.J. Butler, L.E. Caldwell, D.M. Griffith, M.L. Hoppus, K.M. Lausten, A.J. Lister, T.W. Lister, J.W. Meltzer, R.S. Morin, S.A. Sader, L.B. Steward, J.R. Steinman, J.A. Westfall, D.A. Williams, A. Whitman, and C.W. Woodall. 2005. The forests of Maine: 2003. Resource Bulletin NE-164. US Department of Agriculture, Forest Service, Northeastern Research Station, Newton Square, PA. Niven, D.K., J.R. Sauer, G.S. Butcher, and W.A. Link 2004. Christmas Bird Count provides insights into population change in land birds that breed in the boreal forest. American Birds 58:10−20. Orians, G.H. 1985. Blackbirds of the Americas. University of Washington Press, Seattle, WA. Peters, H.S., and T.D. Burleigh. 1951. The Birds of Newfoundland. Houghton Mifflin Co., Boston, MA. Peterson, J.M.C. 1988. Rusty Blackbird, Euphagus carolinus. In R.F. Andrle, and J.R. Carroll, (Eds.). The Atlas of Breeding Birds in New York State. Cornell University Press, Ithaca, NY. Picman, J., M. Leonard, and A. Horn. 1988. Antipredation role of clumped nesting by marsh-nesting Red-winged Blackbirds. Behavioral Ecology and Sociobiology 22:9–15. Picman, J., S. Pribil, and A. Isabelle. 2002. Antipredation value of colonial nesting in Yellow-headed Blackbirds. Auk 119:461−472. Powell, L.L. 2008. Habitat occupancy, status, and reproductive ecology of Rusty Blackbirds in New England. M.Sc. Thesis. University of Maine, Orono, ME. Powell, L.L., T.P. Hodgman, W.E. Glanz, J.D. Osenton, and C.M. Fisher. In press [a]. Nest-site selection and nest survival of Rusty Blackbirds in New England: Does timber management adjacent to wetlands create ecological traps? Condor. Powell, L.L., T.P. Hodgman, and W.E. Glanz. In press [b]. Using Rusty Blackbird home ranges to evaluate the potential utility of non-harvest buffers around wetlands. Condor. Richards, T. 1995. Rusty Blackbird. Euphagus carolinus. Pp. 344−345, In C.R. Foss (Ed.). The Atlas of Breeding Birds of New Hampshire. Arcadia Publishing, Dover, NH. 646 Northeastern Naturalist Vol. 17, No. 4 Ritschel, S.E. 1985. Breeding ecology of the Red-winged Blackbird (Agelaius phoeniceus): Tests of models of polygyny. Ph.D. Thesis. University of California, Davis, CA. Simpson, K., J.N.M. Smith, and J.P. Kelsail. 1987. Correlates and consequences of coloniality in Great Blue Heron colonies. Canadian Journal of Zoology 65:572−577. Taylor, P.D., and M.A. Krawchuk. 2006. Scale and sensitivity of songbird occurrence to landscape structure in a harvested Boreal forest. Avian Conservation and Ecology 1: Art. 5. Available online at http://www.ace-eco.org/issues/archive. php/vol1iss1. Todd, W.E.C. 1963. Birds of the Labrador Peninsula and Adjacent Area. University of Toronto Press, Toronto, ON. West-Eberhard, M.J. 1989. Phenotypic plasticity and the origins of diveristy. Annual review of ecology and systematics 80:249−278. Yasukawa, K., R.A. Boley, J.L. McClure, and J. Zanocco. 1992. Nest dispersion in the Red-winged Blackbird. Condor 94:775–777.