Female Bobolink near nest in a hayfield in the Carden Alvar, 6 July 2016. Photo by Alice Pintaric

American depredation of Bobolink and Eastern Meadowlark nests: An unusual predator of two threatened grassland Alice Pintaric

The Bobolink (Dolichonyx oryzivorus ) and Eastern Meadowlark ( Sturnella magna ) are Threatened in Canada (COSEWIC 2010, 2011), their population trends cor - responding with the steep and constant decline of the grassland guild in North America (Brennan and Kuvlesky 2005). These ground-nesting species rely heavily on agricultural land in Ontario, such as hayfields, to provide nesting habitat during the breeding season (Cadman et al. 2007). Unless nests are situated in habitats of high agricultural intensity such as mowed hayfields or pastures with high livestock densi - ties, predation is the leading cause of nest mortality for most ground-nesting birds (e.g., Dion et al. 2000, Winter et al. 2004, Kerns et al. 2010, Perlut and Strong

Volume 35 Number 2 115 The American Bittern ( lentiginosus ), a secretive bird typically associated with wetlands, sometimes nests in grasslands and hayfields (Svedarsky 1992, Dechant et al. 2002, Lor and Malecki 2006). Its breeding season often overlaps with that of Bobolink and East - ern Meadowlark (COSEWIC 2010, 2011). The American Bittern has been recorded as a carnivore, insectivore, crust - acivore and piscivore water ambusher Figure 1. American Bittern nest found on 1 June with small , amphibians, crayfish, 2015 in a hayfield where Bobolink and Eastern aquatic , small mammals and some Meadowlark nests were being monitored in the birds included in its diet (DeGraaf et al. Carden Alvar. Photo by Alice Pintaric 1985, McBride 1993, Austin and Slivin - ski 2000, Lowther et al. 2009, Baschuk et 2011). Other factors such as distances to al. 2012). I report here a previously habitat edges, vegetation structure and unrecorded type of interaction between height can also affect rates of nest loss American Bittern, and Bobolink and (Dion et al. 2000, Kerns et al. 2010). The Eastern Meadowlark. recorded nest predators of ground-nest - ing grassland birds are typically mam - Observations mals, including ground squirrels These observations were recorded while (Ididomys spp.), raccoons ( Procyon lotor ), conducting a study in an Important Bird weasels ( Mus tela spp.), canids such as Area, the Carden Alvar, near Kirkfield, foxes and coyotes ( Vulpes or Canis spp.), Ontario which is a region characterized by striped skunks ( Mephitis mephitis ), limestone bedrock with shallow soil domestic cats ( Felis catus ), cows ( Bos tau - (Wildlife Preservation Canada et al. rus ) and white-tailed deer ( Odocoileus 2008). The study involved determining virginianus ). Other occasional predators the reproductive success of Bobolink and include snakes, and birds such as Brown- Eastern Meadowlark in hayfields and pas - headed Cowbirds ( Molothrus ater ), tures from 2015-2016. On 1 June 2015, Northern Harriers ( Circus cyaneus ), while searching for Bobolink nests in a Buteo spp. and if mowing occurs, Ring- hayfield site (H4), I discovered an Amer - billed Gulls ( Larus dela warensis ), Ameri - ican Bittern nest containing five eggs (Fig - can Crows ( Corvus bra ch y rhynchos ) and ure 1). The nest was later depredated by Com mon Ravens ( Cor vus corax ) (Dion an unknown predator. During the same et al. 2000, Renfrew and Ribic 2003, Per - breeding season, a field technician and I lut et al. 2006, Ribic et al. 2012). frequently observed what we assumed to be a second pair of American in a marshland bordering another hayfield site (H2) (4 kms away from H4) as both

116 Ontario Birds August 2017 pairs were commonly active during morning point counts. The following year, 2016, my field technicians and I continued the study searching for Bobolink and Eastern Meadowlark nests at the same sites. Once again, we observed two pairs of Ameri - can Bittern which we assumed to be the same individuals that had been seen the preceding year as American Bitterns have relatively high site fidelity (Lor 2007). Two Bobolink nests (H4-1 and H4-2 both containing five eggs found on 2 June 2016) were being monitored in the H4 hayfield in the same area where a pair of American Bitterns was usually spotted. On 17 June 2016, while doing normal nest checks, we noticed prominent trails in the hayfields which led us to an Amer - ican Bittern which we flushed. When we went to monitor H4-1 and H4-2, the trails arrived at these points and much of Figure 2. Eastern Meadowlark nest H2-M1 found on the grass was flattened around the nests. 12 June 2016, presumably depredated by an Ameri - We interpreted the flattened grass as evi - can Bittern. All four eggs had large puncture holes. dence of the American Bittern(s) poten - Figure 3. American Bittern found in front of tially searching for the Bobolink nests or the depredated Eastern Meadowlark nest H2-M1 landing in that location. H4-1 only con - (Figure 2) at a hayfield in the Carden Alvar. tained one nestling and one egg, Photos by Alice Pintaric although it had five offspring on 12 June 2016 during the previous nest check. Eastern Meadowlark nest, H2-M1, Similarly, H4-2 was left with three which was found on 31 May 2016 with nestlings and one egg although it con - four eggs. During our regular nest mon - tained three nestlings and two eggs on 12 itoring on 12 June 2016, we arrived at June 2016. The next subsequent nest H2-M1 to find all four eggs punctured monitoring day, 19 June 2016, we once with the contents removed (Figure 2) again saw signs of the tracks left by the and an American Bittern feather in front American Bittern(s) and both nests were of the nest (Figure 3). This was the only empty. nest of 47 depredated nests in the study At the other hayfield site (H2), where which was found with large puncture the second pair of American Bitterns had holes in the eggs. All other nests had the commonly been observed in the border - contents removed or offspring crushed ing wetland, we were monitoring an due to cattle trampling. Typically, nest

Volume 35 Number 2 117 contents are removed by predators with understanding of predator species is little to no disturbance to the nest. Mice, valuable. Studies that have directly iden - weasels and avian predators will occa - tified the predators of Bobolink and sionally leave eggs at the nest with punc - Meadowlarks have been conducted in ture marks (Wilson et al. 1998, Pietz the United States (Pietz and Granfors and Granfors 2000, Renfrew and Ribic 2000, Renfrew and Ribic 2003, Ribic et 2003). al . 2012). Depending on the specific geography of the study, the range of Discussion potential predator species could be dif - American Bitterns are known as gener - ferent than in Ontario. Novel interac - alist ambush predators which forage in tions such as the ones recorded here wetlands (De Graaf et al. 1985). among the American Bittern, Bobolink Although American Bittern have previ - and Eastern Meadowlark are evidence ously been observed feeding on Sora that we still lack a thorough under - (Porzana carolina ) and sparrows standing of the dynamics of predation (McBride 1993, Austin and Slivinski on grassland breeding birds. The long- 2000), this is the first observation of an term protection of Bobolink and East - American Bittern possibly depredating ern Meadowlark is a priority for bird Bobolink or Eastern Meadowlark nests. conservation programs in Ontario That both of the prey species were (McCracken et al. 2013) but a better Threatened obligate grassland birds grasp of the drivers of productivity in makes the observation even more agricultural habitats is needed for effec - notable. This observation highlights the tive management. range of threats that grassland birds are currently facing. Apart from human Acknowledgements induced threats such as mowing, pasture Special thanks to my supervisor, Dr. Erica management and other forms of habitat Nol and The Couchiching Conservancy, loss, these Threatened species may be specifically Ron Reid, for the opportunity to depredated by a broader range of preda - study Bobolink and Eastern Meadowlark in tors than previously assumed. Peterjohn Carden. I would also like to thank all mem - (2003) summarized the population bers of the field crew: Ginny Moore, Ben trends of North American birds and LeClaire, Kathleen Manson and Elizabeth emphasized the need for further studies Moore. The Nature Conservancy of Canada on the interactions of predator popula - and a local rancher kindly granted access to work at these sites. Funding was provided by tions of nesting birds. Considering that Trent University and the Province of Ontario in a great number of grassland bird (Species at Risk Research Fund for Ontario). species, including Bobolink and Eastern Meadowlark, productivity can be sub - Literature Cited stantially reduced by predation (e.g., Austin, J.E. and M.V. Slivinski , 2000. Renfrew and Ribic 2003, Klug et al. American Bittern depredates Sora. Prairie 2010, Vickery et al. 2017), having an Naturalist 32:59-60.

118 Ontario Birds August 2017 Baschuk, M.S. , N. Koper, D.A. Wrubleski Kerns, C.K. , M.R. Ryan , R.K. Murphy , and G. Goldsborough . 2012. Effects of water F.R. Thompson and C.S. Rubin . 2010. depth, cover and food resources on habitat Factors affecting songbird nest survival in use of marsh birds and waterfowl in boreal northern mixed-grass prairie. Journal of wetlands of Manitoba, Canada. Waterbirds Wildlife Management 74:257–264. 35:44–55. Klug, P.E. , S.L. Jackrel and K.A. With . Brennan, L.A. and W.P. Kuvlesky . 2005. 2010. Linking snake habitat use to nest North American grassland birds: an unfolding predation risk in grassland birds: The dangers conservation crisis? Journal of Wildlife of shrub cover. Oecologia 162:803–813. Management 69:1–13. Lor, S.K. 2007. Habitat use and home range Cadman, M.D. , D.A. Sutherland , of American Bitterns ( Botaurus lentiginosus ) G.G. Beck , D. Lepage and A.R. Couturier . and monitoring of inconspicuous marsh birds 2007. Atlas of the Breeding Birds of Ontario, in northwest Minnesota. PhD Thesis. Univer - 2001-2005. Bird Studies Canada, Environ - sity of Missourri. Columbia, Missourri, USA. ment Canada, Ontario Field Ornithologists, 56–57. Ontario Ministry of Natural Resources, and Lor, S. and R.A. Malecki . 2006. Breeding Ontario Nature, Toronto, xxii + 706 pp. ecology and nesting habitat associations of COSEWIC . 2010. Assessment and status five marsh bird species in Western New York. report on the Bobolink Dolichonyx oryzivorus Waterbirds 29:427–436. in Canada. Committee on the Status of Lowther, P. , A.F. Poole , J.P. Gibbs , Endangered Wildlife in Canada, Ottawa. S. Melvin and F.A. Reid . 2009. American vi + 42 pp. Bittern ( Botaurus lentiginosus ), The Birds COSEWIC . 2011. Assessment and status of North America (P. G. Rodewald, Ed.). report on the Eastern Meadowlark ( Sturnella Ithaca: Cornell Lab of Ornithology; Retrieved magna ) in Canada. Committee on the Status from the Birds of North America. Accessed of Endangered Wildlife in Canada, Ottawa. April 2017. x + 40 pp. McBride, F. 1993. Hammonasset: The Dechant, J.A ., M.L. Sondreal , D.H. John - bittern and the sparrow. Connecticut Warbler son , L.D. Igl , C.M. Goldade , A.L. Zimmer - 13:56–57. man and B.R. Euliss . 2002. Effects of McCracken, J.D. , R.A. Reid , R.B. Renfrew , management practices on grassland birds : B. Frei , A.C. Jalava and A.R. Couturier . American Bittern. Jamestown, ND. 14 pp. 2013. Recovery Strategy for the Bobolink Dion, N. , K.A. Hobson and S. Lariviére . (Dolichonyx oryzivorus ) and Eastern Mead - 2000. Interactive effects of vegetation and owlark ( Sturnella magna ) in Ontario. Ontario predators on the success of natural and simu - Recovery Strategy Series. Ontario Ministry of lated nests of grassland songbirds. Condor Natural Resources, Peterborough, Ontario. 102:629–634. Perlut, N.G. and A.M. Strong . 2011. DeGraaf, R.M. , N.G. Tilghman and Grassland birds and rotational-grazing in S.H. Anderson . 1985. Foraging guilds of the northeast: Breeding ecology, survival North American birds. Environmental and management opportunities. Journal Management 9:493–536. of Wildlife Management 75:715–720.

Volume 35 Number 2 119 Perlut, N.G. , A.M. Strong , T.M. Donovan Vickery, P.D. , M.L. Hunter , J.V Wells , and N.J. Buckley . 2006. Grassland songbirds P.D. Vickery , M.L. Hunter , J.V Wells, H. Jr. in a dynamic management landscage: Behav - and J.V. Evidence . 2017. Evidence of inciden - ioural responses and management strategies. tal nest predation and its effects on nests of Ecological Society of America 16:2235–2247. threatened grassland birds. Oikos 63:281-288. Peterjohn, B.G. 2003. Agricultural land - Wildlife Preservation Canada, The Couch - scapes: Can they support healthy bird iching Conservancy and The Nature Conser - populations as well as farm products? vancy of Canada . 2008. Towards an integrat - Auk 120:14–19. ed Carden conservation strategy. Part 1: Pietz, P.J. and D.A. Granfors . 2000. Identify - Healthy ecosystems & species at risk. 1-42. ing predators and fates of grassland passerine Wilson, G.R. , M.C. Brittingham and nests using miniature video cameras. Journal L.J. Goodrich . 1998. How well do artificial of Wildlife Management 64:71–87. nests estimate success of real nest s? Condor Renfrew, R.B. and C.A Ribic . 2003. 100:357–364. Grassland passerine nest predators near Winter, M. , D.H. Johnson , J.A Shaffer and pasture edges identified on videotape. W.D. Svedarsky . 2004. Nesting biology of Auk 120:371–383. three grassland passerines in the northern tall - Ribic, C.A. , F.R. Thompson and P.J. Pietz . grass prairie. Wilson Bulletin 116:211–223. 2012. Video surveillance of nesting birds. University of California Press. 240 pp. Alice Pintaric Svedarsky, W.D. 1992. Observations on Trent University, 1600 West Bank Dr. nesting of the American Bittern in northwest Peterborough, Ontario K9J 0G2 Minnesota. Prairie Naturalist 24:241–250. E-mail: [email protected] The birds are calling! Festival of Hawks Sept. 9-10 & 16-17, 2017 Holiday Beach Conservation Area

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120 Ontario Birds August 2017