Sandhill crane colt survival and fledging success in northeastern Illinois: the role of age and significance of land cover in an urbanized landscape
The breeding and fledging success of Sandhill Cranes (Grus canadensis spp.) in urban landscapes has been largely unexplored by previous research. I evaluated survival and habitat use of young Greater Sandhill Cranes (G. c. tabida) in northeastern Illinois, where the Eastern Population of cranes and urban sprawl have concurrently increased for several decades. Using an information-theoretic approach to evaluate fates of 85 radio-marked young (i.e. 1 to 10 week old cranes; a.k.a. colts) revealed age was the most influential factor and the age-based probability of surviving to fledge (≈10 weeks old) was 32.44%. Birds hatched before the end of May hatched from nests in significantly larger wetland complexes and survived better than those hatching after May (35.55% and 10.34%, respectively). This was likely due to experienced breeders nesting early and in larger wetland habitats. Surprisingly, colt survival was positively correlated with urban development and declined with increases in grassland/savanna or agricultural land cover. I hypothesize that cranes acclimated to humans were buffered from predation by the human-avoidance behaviors and hunting habits of common colt predators in the region. However, while I did not observe competition within broods (i.e. sibling-strife) and neither the presence of nor size of siblings significantly affected survival, sibling fates were strongly correlated with each other and the mortality of one colt reduced the probability of the other fledging by 32.94%. Overall fledging success in northeastern Illinois appeared to be lower than previously reported throughout much of the literature on colt survival. It is therefore unlikely that birds hatched and fledged in northeastern Illinois are significantly contributing to the rapid growth of the Eastern Population observed in the region. Additional research is warranted to facilitate crane conservation efforts as cranes and urban sprawl continue to overlap.
Sandhill Crane, Colt Survival, Fledging Success, Urban
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign