Date of this Version
Nesbitt, S.A., P.S. Kubilis, and S.T. Schwikert. Response of Florida sandhill cranes to nest inspection. In Chavez-Ramirez, F, ed. 2005. Proceedings of the Ninth North American Crane Workshop, Jan 17-20, 2003. Sacramento, California: North American Crane Working Group. Pp. 241-246.
We observed the response of nesting Florida sandhill cranes (Grus canadensis pratensis) to 27 instances of nest inspection. The disturbed bird flew from the area 81% and walked 19% of the time. The median distance moved was 330 meters (range 28 to 480 meters). The median length of time the nest was left unattended following inspection was 50 min (range: 10 to 166 min). The median length of time that observers stayed at the nest was 16 min (range: 5 to 48 min). Ten of the nests inspected (40%) eventually failed to produce young. Statistical analysis was focused on the direction and strength of association between various predictors and 4 disturbance-related outcomes; flying vs. walking, distance moved, time-off-nest, and nest fate. A limited sample size precluded the use of more than 2 predictors simultaneously in any of the statistical models. We found that the farther into incubation the nest was (nest age) the greater the likelihood the incubating bird would fly from the nest (r2=0.28, P= 0.064). Greater time-in nest area was associated with a longer time-off-nest (r2=0.29, P= 0.008). Greater time-in nest area and longer time-off-nest were both univariantely associated with a greater probability of nest failure (r2=0.36, P=0.018 and r2=0.40, P=0.008 respectively). Four variables (time-in-area, time-off-nest, age of nest, whether the disturbed crane or its mate returned to the nest) considered in pair wise combinations were all significantly associated with probability of nest failure (r2 range: 0.46 to 0.72). Longer time-in-area and whether the disturbed bird was the returning bird had the strongest overall association with likely nest failure (r2=0.72, P=0.010). Although the nest failure rate of 44% in the experimental nests was greater than the failure rate of 26% for a concurrently collected sample of control nests, the 2 rates were not significantly different (P=0.353). Based on these results we would recommend that crane nests be inspected in 12-13 min or less. If possible, nest inspections should occur later rather than earlier in the incubation period, carried out in a manner that increases the likelihood that the disturbed bird will walk rather than fly from the nest area, and timed to increase the chance that the non-disturbed bird will be the returning bird.