Infrequent Cowbird Parasitism on Common Grackles Revisited: New Records from the Northern Great Plains

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June 2001

INFREQUENT COWBIRD PARASITISM ON COMMON GRACKLES REVISITED: NEW RECORDS FROM THE NORTHERN GREAT PLAINS

Brian D. Peer Lawrence Univ., Appleton, WI

H. Jeffrey Homan USDA/National Wildlife Research Center/Great Plains Field Station

Spencer G. Sealy Univ. of Manitoba, Winnipeg, MB, Canada

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Peer, Brian D.; Homan, H. Jeffrey; and Sealy, Spencer G., "INFREQUENT COWBIRD PARASITISM ON COMMON GRACKLES REVISITED: NEW RECORDS FROM THE NORTHERN GREAT PLAINS" (2001). USDA National Wildlife Research Center - Staff Publications. 535. https://digitalcommons.unl.edu/icwdm_usdanwrc/535

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INFREQUENT COWBIRD PARASITISM ON COMMON GRACKLES REVISITED: NEW RECORDS FROM THE NORTHERN GREAT PLAINS

BRIAN D. PEER,1,4 H. JEFFREY HOMAN,2 AND SPENCER G. SEALY3

ABSTRACT.ÐWe report nine new records of Brown-headed Cowbird (Molothrus ater) parasitism on the Common Grackle (Quiscalus quiscula): six from Benson County, North Dakota, and three from Delta Marsh, Manitoba. These observations represent 30% of the total number of records of parasitism on this host. Parasitism frequencies were 0.8% of 727 nests in North Dakota, and 4.0% of 75 nests in Manitoba. The data from Manitoba, combined with previous data from this location (Neudorf and Sealy 1994), yields a parasitism frequency of 3.4% of 119 nests examined. These parasitism frequencies are the highest recorded for the Common Grackle. Received 2 June 2000, accepted 2 February 2001.

Survival of obligate avian brood parasites suitable hosts. Peer and Bollinger found that demands that they lay their eggs in nests of 20% of cross-fostered cowbird nestlings hosts that are capable of successfully rearing ¯edged from grackle nests. Two noteworthy the parasite's young. Host selection by the ®ndings from their study were that grackles parasitic Brown-headed Cowbird (Molothrus responded more aggressively to cowbird mod- ater), however, is often enigmatic. Frequen- els than to control models, suggesting some cies of cowbird parasitism vary geographical- recognition of cowbirds as a threat, and that ly for appropriate hosts (Robinson et al. 1995, grackles demonstrated a low level of egg ejec- Peer et al. 2000), and hosts that are unsuitable tion behavior (see also Rothstein 1975, Sealy because their nests are inaccessible or they are et al. 1998). Peer and Bollinger (1997a) ar- incapable of rearing brood parasites some- gued that cowbirds avoid grackles as potential times are parasitized more often than suitable hosts because historically grackles may have hosts (Rothstein 1976, Ortega and Cruz 1991, rejected most cowbird eggs from their nests. Kozlovic et al. 1996, Peer and Bollinger In the absence of parasitism, Common Grack- 1997a). les may have lost the advantages of rejection Among the rarely parasitized but suitable behavior and increased the risk of ejecting cowbird hosts is the Common Grackle (Quis- their own eggs due to their highly variable calus quiscula). The Common Grackle previ- appearance within clutches (Peer and Bollin- ously has been reported parasitized by the ger 1997a, Peer 1998). In support of this, Peer Brown-headed Cowbird only 21 times, despite (1998) found that Common Grackles demon- ranging widely across North America in the strated the lowest level of egg rejection among cowbird's range (Peer and Bollinger 1997b; the rarely, if ever, parasitized members of see also Fleischer 1986). Friedmann et al. Quiscalus, and the highest level of intraclutch (1977) commented on the curious lack of variation in egg appearance. Here we report cowbird parasitism on Common Grackles, nine new records of parasitism on the Com- which prompted the experiments by Peer and mon Grackle from the northern Great Plains Bollinger (1997a) that demonstrated that de- and review this grackle's status as a host of spite their large size, Common Grackles are the Brown-headed Cowbird. METHODS 1 Dept. of Biology, Lawrence Univ., Appleton, WI Common Grackle nests were observed from 1989 to 54912. 1990 in Benson County, North Dakota (48Њ 00Ј N, 99Њ 2 USDA/National Wildlife Research Center/Great 20Ј W), and from 1992 to 1995 at Delta Marsh, Man- Plains Field Station, 2110 Miriam Circle, Suite B, Bis- itoba (50Њ 11Ј N, 98Њ 19Ј W). Benson County is typi- marck, ND 58501. ®ed by croplands interspersed with numerous wetlands 3 Dept. of Zoology, Univ. of Manitoba, Winnipeg, and shelterbelts. Most grackle nests in Benson County MB R3T 2N2, Canada. were located in shelterbelts and were observed only 4 Corresponding author; E-mail: brian.d.peer@ once as part of a study of nest-site selection (Homan lawrence.edu et al. 1996). The Delta Marsh study area is located on 90 Peer et al. • COWBIRD PARASITISM ON COMMON GRACKLES 91 the southern end of Lake Manitoba (see MacKenzie 1982 for details). Grackle nests were found at the edge TABLE 1. Known records of Brown-headed of the marsh and in and along ditches south of the Cowbird parasitism on Common Grackles. forested dune ridge. Nests were typically placed in cat- Parasitism tails (Typha spp.) and phragmites (Phragmites com- events (total number munis), though some were in willows (Salix spp.). Un- Location of nests) References like the North Dakota portion of our study, the focus Illinois 4 (?) Friedmann (1963) of the Manitoba study was on cowbird parasitism. Iowa 1 (46) Lowther (1991) Nests were monitored daily through at least clutch Kansas 1 (23) Fleischer (1986) completion for evidence of cowbird parasitism. Most Manitoba 1 (44) Neudorf and Sealy (1994) 3 (75) This study nests (77%) in Manitoba were also experimentally par- Maryland 1 (?) Friedmann et al. (1977) asitized with model cowbird eggs. All potential habitat Minnesota 2 (?) Friedmann and Kiff (1985) at both the Benson County and Delta Marsh sites was Nebraska 1 (?) Friedmann et al. (1977) New York 2 (?) Friedmann et al. (1977) searched thoroughly for grackle nests. Nests in North North Dakota 1 (?) Friedmann (1963) Dakota were checked only for the presence of cowbird 6 (727) This study 1 eggs, not nestlings; thus nests that contained only nes- Ontario 4 (2091) Peck and James (1987) Saskatchewan 2 (?) Friedmann and Kiff (1985) tlings were excluded from the data set. We de®ned a Texas 1 (?) Friedmann (1963) grackle colony as Նthree nests within 10 m of one Total 30 another (Peer and Bollinger 1997a). 1 Friedmann et al. (1977) reported a parasitized nest in Ontario from the Ontario Nest Record Program. We assume this record is among those reported by Peck and James (1987), hence, we did not include Friedmann's RESULTS AND DISCUSSION reference to this record in this list. Six parasitism events were recorded at 727 nests (0.82%) in North Dakota. One nest third parasitized nest was found on 22 May found on 6 June 1989 contained two grackle 1995 containing ®ve host eggs and one cow- eggs and one cowbird egg. Five parasitized bird egg. The cowbird egg was subsequently nests were found in 1990. On 29 and 31 May, depredated. All of the parasitized nests in each of two nests held three host eggs and one Manitoba were in colonies; thus eight of the cowbird egg, and also on 31 May, a second nine parasitized nests from our study were lo- nest contained three host eggs and two cow- cated in colonies. The data from Manitoba, bird eggs. Two more nests were found within combined with previous data from this site the same colony on 7 June: one with one host (Neudorf and Sealy 1994), yields a parasitism egg and a cowbird egg, and the other with one frequency of 3.4% on 119 nests. Experimental host egg and two cowbird eggs. Five of the addition of cowbird eggs to grackle nests in six parasitized nests were located in colonies. Manitoba may have affected natural cowbird There was no signi®cant difference in the par- behavior. Similar to the ®ndings of Ortega and asitism frequency for the two years (1/161 coworkers (1994), nests that were experimen- nests in 1989, 5/566 in 1990; Fisher exact test, tally parasitized were naturally parasitized less P Ͼ 0.99). We may have underestimated the frequently than unmanipulated nests. There- parasitism frequency in North Dakota because fore our experiments may have made cow- no attempt was made to detect cowbird nest- birds less inclined to parasitize these nests. lings, and these nests were observed only Nevertheless, these data still represent the once, so cowbird eggs may have been rejected highest parasitism frequencies reported for by grackles before nests were observed or this host. nests may have been parasitized later. Al- The nine new cases of cowbird parasitism though possible, it probably did not in¯uence represent 30% of the total parasitism events our results signi®cantly because grackles re- recorded for the Common Grackle. In addition ject cowbird eggs infrequently (12±17%; to those listed in Peer and Bollinger's review Rothstein 1975, Peer and Bollinger 1997a). (1997b), and one from Fleischer (1986), these In Manitoba, three of 17 unmanipulated bring the total number of records of parasitism nests were parasitized, compared with 0 of 58 to 30 (Table 1). Despite the relatively large manipulated nests (Fisher exact test, P ϭ number of parasitized nests, the parasitism 0.01). Two nests found in the same colony on frequencies were still low, 3.4% at Delta 24 and 25 May 1992 each contained one cow- Marsh being the highest. The low frequency bird egg and one host egg. Both cowbird eggs of parasitism is also evident from the follow- were removed for other experiments. The ing data sets: 0 of 1795 nests (Friedmann et 92 THE WILSON BULLETIN • Vol. 113, No. 1, March 2001 al. 1977), 0 of 371 nests (Goertz 1977), 4 of ACKNOWLEDGMENTS 2091 nests (Peck and James 1987), and 0 of The North Dakota data were collected with the sup- 401 nests (Peer and Bollinger 1997a). Hence, port of the USDA, NWRC, Ft. Collins, CO, and the the Common Grackle is a very rare host of Department of Zoology, North Dakota State Univer- the cowbird, perhaps the least frequently used sity, Fargo, ND. P. N. HeÂbert, J. C. Lorenzana, C. M. of all suitable hosts. McLaren, and D. L. Neudorf provided ®eld assistance Common Grackles are among the earliest at Delta Marsh. The University of Manitoba Field Sta- tion provided living accommodations at Delta Marsh, nesting passerines in North America, with the and funding for this portion of the study was provided peak of clutch initiation occurring in mid- to by a Natural Sciences and Engineering Research late April in the Midwest (Peer and Bollinger Council of Canada grant to SGS. 1997a, b). Peer and Bollinger (1997a) found that 89% of grackle nests in Illinois were be- LITERATURE CITED yond the point of successful parasitism when FLEISCHER, R. C. 1986. Brood parasitism by Brown- cowbirds began laying, which suggests that headed Cowbirds in a simple host community in the mismatch of grackle and cowbird breeding eastern Kansas. Kansas Ornithol. Soc. Bull. 37: seasons may contribute to the low levels of 21±29. FRIEDMANN, H. 1963. Host relations of the parasitic parasitism there. However, Peer and Bollinger cowbirds. U.S. Natl. Mus. Bull. No. 233. (1997a) noted that despite this, more grackle FRIEDMANN,H.AND L. F. KIFF. 1985. The parasitic nests were available for parasitism than all cowbirds and their hosts. West. Found. Vert. Zool. other host species in the community except 2:225±304. one, indicating that grackle nests were avoid- FRIEDMANN, H., L. F. KIFF, AND S. I. ROTHSTEIN. 1977. A further contribution to knowledge of the host ed. In Manitoba, grackles arrive in late March relations of the parasitic cowbirds. Smithson. Con- through April, and although the ®rst clutches trib. Zool. No. 235. are initiated in early May, most laying occurs GOERTZ, J. W. 1977. Additional records of Brown- during the latter half of May (SGS, pers. obs.). headed Cowbird nest parasitism in Louisiana. Auk Cowbirds begin arriving about the end of the 94:386±389. ®rst week of May and begin laying shortly HOMAN, H. J., G. M. LINZ,W.J.BLEIER, AND R. B. CARLSON. 1996. Colony-site and nest-site use by thereafter (SGS, pers. obs.). Thus, the more Common Grackles in North Dakota. Wilson Bull. closely aligned breeding seasons of the two 108:104±114. species may contribute to the higher parasit- KOZLOVIC, D. R., R. W. KNAPTON, AND J. C. BARLOW. ism frequencies recorded in the northern Great 1996. Unsuitability of the House Finch as a host Plains. of the Brown-headed Cowbird. Condor 98:253± Cowbirds may parasitize Common Grack- 258. LOWTHER, P. E. 1991. Catalog of Brown-headed Cow- les early in the cowbird's laying season in bird hosts from IowaÐan update. Iowa Bird Life Manitoba because few alternate hosts nest that 61:33±39. early. Indeed, a grackle nest parasitized on 15 MACKENZIE, D. I. 1982. The dune-ridge forest, Delta May 1991 was the earliest record of parasit- Marsh, Manitoba: overstory vegetation and soil ism recorded on any species at Delta Marsh patterns. Can. Field-Nat. 96:61±68. NEUDORF,D.L.AND S. G. SEALY. 1994. Sunrise nest in nearly 30 yr of observations (Neudorf and attentiveness in cowbird hosts. Condor 96:162± Sealy 1994; SGS, pers. obs.). Most known ob- 169. servations of parasitism on the Common ORTEGA, C. P. 1998. Cowbirds and other brood para- Grackle (77%) are from the Great Plains (Ta- sites. Univ. of Arizona Press, Tucson. ble 1) and perhaps not coincidentally cowbird ORTEGA,C.P.AND A. CRUZ. 1991. A comparative population densities are highest there (Price et study of cowbird parasitism in Yellow-headed Blackbirds and Red-winged Blackbirds. Auk 108: al. 1995, Ortega 1998). Greater densities of 16±24. cowbirds in the northern Great Plains may ORTEGA, C. P., J. C. ORTEGA, AND A. CRUZ. 1994. Use lead to higher frequencies of parasitism on of arti®cial Brown-headed Cowbird eggs as a po- rarely used hosts such as the Common Grack- tential management tool in deterring parasitism. J. le. In addition to the more closely matched Wildl. Manage. 58:488±492. PECK,G.K.AND R. D. JAMES. 1987. Breeding birds of breeding seasons of cowbirds and grackles, Ontario: Nidiology and distribution. Vol. 2: pas- this may explain the relatively high frequen- serines. Royal Ontario Museum, Toronto, Ontario, cies of parasitism we observed for this host. Canada. Peer et al. • COWBIRD PARASITISM ON COMMON GRACKLES 93

PEER, B. D. 1998. An experimental investigation of ROBINSON, S. K., S. I. ROTHSTEIN,M.C.BRITTINGHAM, egg rejection behavior in the grackles (Quiscalus). L. J. PETIT, AND J. A. GRZYBOWSKI. 1995. Ecology Ph.D. thesis, Univ. of Manitoba, Winnipeg. and behavior of cowbirds and their impact on host PEER,B.D.AND E. K. BOLLINGER. 1997a. Explanations populations. Pp. 428±460 in Ecology and man- for the infrequent cowbird parasitism on Common agement of neotropical birds (T. E. Martin and D. Grackles. Condor 99:151±161. M. Finch, Eds.). Oxford Univ. Press, New York. PEER,B.D.AND E. K. BOLLINGER. 1997b. Common ROTHSTEIN, S. I. 1975. An experimental and teleonom- Grackle (Quiscalus quiscula). In The birds of ic investigation of avian brood parasitism. Condor North America, no. 271 (A. Poole and F. Gill, 77:250±271. ROTHSTEIN, S. I. 1976. Cowbird parasitism of the Ce- Eds.). The Academy of Natural Sciences, Phila- dar Waxwing and its evolutionary implications. delphia, Pennsylvania; the American Ornitholo- Auk 93:498±509. gists' Union, Washington, D.C. SEALY, S. G., D. L. NEUDORF,K.A.HOBSON, AND S. PEER, B. D., S. K. ROBINSON, AND J. R. HERKERT. 2000. A. GILL. 1998. Nest defense by potential hosts of Egg rejection by cowbird hosts in grasslands. Auk the Brown-headed Cowbird; methodological ap- 117:892±901. proaches, bene®ts of defense, and coevolution. Pp. PRICE, J., S. DROEGE, AND A. PRICE. 1995. The summer 194±211 in Parasitic birds and their hosts: studies atlas of North American birds. Academic Press, in coevolution (S. I. Rothstein and S. K. Robin- New York. son, Eds.). Oxford Univ. Press, New York.