Late laying by a Brown-headed cowbird, in an american goldfinch nest Spencer G. Sealy Saskatchewan5,6, the low frequency first goldfinch egg was laid.4 Department of Biological Sciences of parasitism on American Goldfinch The span of laying dates over the University of Manitoba is typical of most other localities cowbird’s breeding season has not Winnipeg, MB R3T 2N2 where nests of this species have been determined in Saskatchewan, [email protected] been studied.1,2,7 Of 33 goldfinch but at Delta Marsh, Manitoba, most nests reported from Saskatchewan cowbirds cease laying by the time Infrequent parasitism on the to the Prairie Nest Records Scheme their primary hosts (Yellow Warbler American Goldfinch (Spinus tristis) (PNRS), three (9.1%) were parasitized [Setophaga petechia], Red-winged by the Brown-headed Cowbird by cowbirds whose eggs were first Blackbird [Agelaius phoeniceus], and (Molothrus ater) has usually been recorded on 19 July 1967 at Yellow Song Sparrow [Melospiza melodia]) explained by the potential host’s late- Creek (PNRS card #25114); on have ceased laying, in late June or nesting schedule.1,2 At parasitized 27 June 1969 at Lady Lake (PNRS during the first few days of July.11-13 goldfinch nests, cowbird chicks #25123); and on 18 June 1974 at This was confirmed by superimposing generally do not survive the nestling Hagen (PNRS #25128). As these cowbird laying dates on clutch- period due to incompatibility of the nests were not inspected daily, initiation dates of the Yellow Warbler, diet of the host (regurgitated seeds) exact laying dates of goldfinches or based initially on data collected from and parasite (insects).3,4 The breeding cowbirds were not determined. Fates 1974 to 1976.11 The last warbler seasons of these species overlap of the single cowbird eggs in these clutch was initiated on 2 July 1974 only to a small extent, such that by nests were: (1) buried under a new (last cowbird egg laid 2 July), on 7 the time the last cowbird eggs are nest lining (Hagen); (2) disappeared July 1975 (9 July, in 3-egg clutch), laid, goldfinches have only begun at least nine days into incubation and on 6 July 1976 (23 June 1976). to initiate clutches. The relationship (Lady Lake); and goldfinch and Data collected on Yellow Warblers between the two species in this cowbird nestlings disappeared eight between 1994 and 1998 revealed rather short period of overlap has days after hatching, apparently last cowbird eggs were laid on 28 or been studied most extensively in depredated (Yellow Creek). 29 June in four of the years, but on 9 southern Ontario.2,4 Of 802 goldfinch To this total, from field notes July in 1994.12 nests, 47 (5.7%) were parasitized, made at the time of the original Exceptionally late cowbird but only 13 eggs hatched, and no observations, I report cowbird laying dates were recorded at Delta cowbirds fledged. The author stated, parasitism on a goldfinch nest Marsh, at nests of two species: Least “…although the cowbird gained located near Prongua, Saskatchewan Flycatcher (Empidonax minimus) on little advantage from the association, (52°74’ N,108°55’ W), about 17 km 12 July 1980 and Cedar Waxwing its parasitism largely offset the south of Battleford. On 10 July 1980, (Bombycilla cedrorum) on 13 advantages of early nesting by the a nest about 2 m high in a Trembling July 1996. Even later, a cowbird adult goldfinches. The goldfinch has Aspen (Populus tremuloides) fledgling being fed by a Common not developed any apparent defense contained four goldfinch eggs plus Yellowthroat (Geothlyis trichas) on against cowbird parasitism, but those one cowbird egg. Two days later, 20 August 199213 probably hatched individuals that nested in man- the nest contained a fifth and final no earlier than 15 July. These made habitats were largely free of goldfinch egg, assuming the cowbird observations revealed some adult its influence.”2 In this note, I report did not remove a goldfinch egg female cowbirds remained through cowbird parasitism on an American around the time of parasitism2,9, the middle of July after most other Goldfinch nest near Battleford, as six-egg goldfinch clutches have adults and juveniles have left the Saskatchewan. The late date of been recorded in Saskatchewan.8,10 area14,15, apparently having migrated. laying is confirmed by comparison The cowbird’s egg probably was laid None of the ~1,100 cowbirds with cowbird laying dates recorded on 6 or 7 July 1980, as goldfinch banded at Delta Marsh16 was at Delta Marsh, Manitoba. nests are normally parasitized the encountered during southward Listed as a cowbird host in morning before or on the day the migration or on the wintering

36 BLUE JAY Summer 2020 volume 78.2 ground, but an adult male banded the host relations of the parasitic cowbirds. at Muscow, Saskatchewan, on Smithsonian Contributions to Zoology, Number 235. 13 June 1929, and found dead Poetry in New Mexico about two weeks 4. Middleton ALA (1991) Failure of Brown- later, provides anecdotal support headed Cowbird parasitism of the American Goldfinch. Journal of Field Ornithology for early departure and long- 62:200-203. Cloudy With distance southward migration from Sunny Breaks 5. Friedmann H (1963) Host relations of the Saskatchewan.6 parasitic cowbirds. United Sates National Female cowbirds at the northern Museum Bulletin, Number 233. Four or five Ravens edge of their range that remain at 6. Sealy SG (2019) Brown-headed Cowbird. blacken before a flock the breeding sites well into July have Pages 636-638 in Birds of Saskatchewan fewer opportunities for parasitism (Smith AR, Houston CS, Roy JF, editors). of Snow Geese streaming as most individuals of the primary Nature Saskatchewan, Regina. home from the south. 11,12 host species have ceased laying , 7. Peck GK, James RD (1987) Breeding leaving available nests of mostly birds of Ontario: Nidiology and distribution, Reflecting the sunlight poor hosts. Factors that influence Volume 2: Passerines. Royal Ontario they are silver and blue decisions of cowbirds leading up to Museum, Toronto. termination of laying and southward 8. Kratzig GP, Houston CS (2019) American in their barking flight migration are important avenues for Goldfinch. Pages 663-665 in Birds of upon brooding grey skies. further study. Saskatchewan (Smith AR, Houston CS, Roy JF, editors). Nature Saskatchewan, Regina. Acknowlegements 9. Sealy SG (1992) Removal of Yellow I am indebted to Glenn C. Sutter, Warbler eggs in association with cowbird parasitism. Condor 94:40-54. Royal Saskatchewan Museum, George Grassick for providing data for American 10. Hooper DF (1992) Birds of East-Central Box 205 Goldfinch nests contained in the Saskatchewan, Kelvington to Kelsey Trail. Lumsden, SK Saskatchewan Natural History Society Special files of the PNRS. A big thank you S0G 3C0 Publication, Number 18. to the individuals who took time to [email protected] submit nest cards to the PNRS, thus 11. Goossen JP (1978) Breeding biology and reproductive success of the Yellow Warbler contributing to an important source on the Delta Beach Ridge, Manitoba. M.Sc. of information. Paul Goossen’s and thesis, University of Manitoba, Winnipeg. Bonnie Woolfenden’s inspections of 12. Woolfenden BE, McLaren CM, Sealy SG, nests provided data on the seasonal Gibbs HL (2004) Community-level patterns pattern of cowbird parasitism on the of parasitism: Use of three common host primary host species at Delta Marsh, species by a brood parasitic bird, the Brown- in the 1970s and 1990s, respectively. headed Cowbird. Écoscience 11:238-248. Gloria Biermann Pohajdak and Glen 13. Sealy SG (2016) Additional observations McMaster discovered the parasitized of putative host species feeding only nests of Least Flycatcher and Cedar cowbird fledglings. Blue Jay 74(3):28-31. Waxwing, respectively. I thank an 14. Woolfenden BE, Gibbs HL, Sealy SG anonymous reviewer for constructive (2001) Demography of Brown-headed comments on the manuscript. Cowbirds at Delta Marsh, Manitoba. Auk 118:156-166. 1. Friedmann H, Kiff LF (1985) The parasitic cowbirds and their hosts. Proceedings of the 15. Holland GE, Taylor P (2003) Brown- Western Foundation of Vertebrate Zoology headed Cowbird. Pages 382-383 in The 2:226-302. Birds of Manitoba, Manitoba Naturalists Society, Winnipeg. 2. Middleton ALA (1977) Effect of cowbird parasitism on American Goldfinch nesting. 16. Sealy SG (2019) Report on birds banded Auk 94:304-307. in the dune-ridge forest, Delta Marsh, Manitoba, 1973-1988. Blue Jay 77(1):42-47. 3. Friedmann H, Kiff LF, Rothstein SI (1977) A further contribution to knowledge of

Summer 2020 volume 78.2 BLUE JAY 37