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COPYRIGHT 2005 Wilson Ornithological Society
ABSTRACT.--We document the first cases of cattle behaving as avian predators, removing nestlings and eggs from three active ground nests in continuously grazed pastures in southwestern Wisconsin, 2000-2001. Cows removed three of four Savannah Sparrow (Passerculus sandwichensis) eggs from one nest (the fourth egg was damaged), all four Eastern Meadowlark (Sturnella magna) nestlings from another, and all three Savannah Sparrow nestlings from a third. We found only two of three missing eggs (intact) and one of seven missing nestlings (dead) near two of the nests. Cows may have eaten the egg and nestlings we were unable to account for; alternatively, the egg and nestlings may have been scavenged by predators or removed from the area by the adult birds. Without videotape documentation, we would have attributed nest failure to traditional predators and cattle would not have been implicated. We may be underestimating the impact of cattle on ground nests by not considering cattle as potential predators. Received 10 May 2004, accepted 6 December 2004.
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Over the last 30 years, grassland birds have declined more rapidly and consistently than any other avian guild in the Midwest (Vickery and Herkert 2001). One possible cause is the loss and fragmentation of native and secondary grasslands (Sample et al. 2003). Herkert et al. (1996) found a significant correlation between the decline of grassland birds in the Midwest and the conversion of hay and pasture acreage to row crops and other unsuitable habitat. Since the conversion of land from native prairie to agriculture during European settlement, secondary grasslands, such as pastureland, have become critical components of grassland passerine conservation (Herkert 1991, Herkert et al. 1996, Sample and Mossman 1997).
Nest predation is a major factor in the nesting failure of most passerine species (Lack 1968, Ricklefs 1969, Martin 1988). This may be a particular problem in grassland ecosystems where generalist predators, such as raccoons (Procyon lotor) and skunks (Mephitis spp.), have responded positively to human disturbance and landscape fragmentation (Sargeant et al. 1993, Warner 1994). In actively grazed pastures, ground-nesting grassland birds face additional risks from cattle. In southwestern Wisconsin, Temple et al. (1999) thought that many of the nest losses incurred by grassland birds in grazed pastures were a result of cattle trampling and nest desertion after cattle had grazed down the vegetation surrounding the nest.
In previous literature on cattle disturbance to bird nests, authors have used sign to interpret the occurrence of cattle disturbance, mainly at artificial nests and under rotational grazing regimes (Paine et al. 1996, 1997). Under a rotational grazing regime at the University of Wisconsin's Lancaster Agricultural Research Station in southwestern Wisconsin, Paine et al. (1996) documented cattle disturbance resulting in nest failure at simulated ground nests in which Ring-necked Pheasant (Phasianus colchicus) eggs had been placed. Ninety-four percent of failed nests were the result of cattle damage. Nest disturbance included nest contents being trampled, kicked out, crushed by the animal's muzzle, or covered with a manure pile. The mean percentage of nests (n = 15) having [greater than or equal to] 1 egg trampled by a bovine hoof was 63% for the 1-day treatment, 52% for the 4-day treatment, and 41% for the 7-day treatment.
In a refinement of their 1996 study, Paine et al. (1997) documented cattle sniffing, licking, and occasionally picking up contents of simulated ground nests (clay...
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