Date of this Version
PROCEEDINGS OF THE NORTH AMERICAN CRANE WORKSHOP 14:67-80
Damage to corn in the spring caused by greater sandhill cranes (Grus canadensis tabida) has increased concurrent with growth of the Eastern Population of cranes. Our study was designed to: 1) describe foraging rates and food acquisition behavior where damage was likely and 2) estimate damage in cornfields treated and untreated with a taste deterrent: 9,10-anthraquinone (AQ; Avipel®). Our 6,251.6-ha study area was located near Briggsville, Wisconsin, and we sampled 415 ± 13.2 individuals/ survey (x ± SE), of which 36 ± 1.7% used cornfields. During 10-30 May 2009, 121 observation bouts of 33 marked cranes that foraged in 20 cornfields were collected. Observation bouts averaged 21 ± 1.32 minutes of which 10.2 ± 0.75 minutes consisted of active foraging by cranes. Individuals swallowed an average of 6.08 ± 0.68 items/active minute. Only 10.4% of 6,445 items consumed were identified and 9.7% of items were corn kernels (93% of identified items). Ingestion rates for all foods in fields treated with AQ (6.44 items/min) and non-treated fields (6.21 items/min) did not differ (t = −0.15, P = 0.88), but corn kernels consumed in non-treated fields were ingested at more than 3 times the rate measured from treated fields (F = 3.84, P = 0.05). Jab/probe ratios did not differ between treated and untreated fields (F = 0.12, P = 0.72), so foraging behaviors were similar even though different foods were consumed. We estimated that all sandhill cranes in this study area consumed 71,245 kernels/ day (478 kernels/crane/day) and, over the period that planted corn was potentially vulnerable, consumed a maximum of >2.9 million kernels or 41.0 ha of planted corn (3.8% of all corn planted in the study area). Crane damage could be widely scattered, and thus insignificant, or it could be locally severe as non-territorial individuals congregate in 1 field and concentrate damage, making the distribution of severe damage unpredictable. Though effective at alleviating crane damage, treating planted corn must either be applied uniformly or applied based on previous experience with crane foraging patterns and planting phenology in relationship to other fields.