Dr. Mark Boyce, from the Faculty of Science, studied the policy of removing from Wood Buffalo National Park one of two whooping crane eggs laid and raising it in a "foster-parenting" program. Cranes usually rear a single chick and the other dies to siblicide or is killed by a predator, such as the wolf or fox. The egg-removal program was initiated years ago by Ernie Kuyt, an Edmonton-based scientist who reasoned that one egg could be taken and used for artificial propagation programs. The idea was so successful, says Boyce, that the whooping crane's numbers have skyrocketed to over 200 birds in the original population and two new populations have been established elsewhere.
But Parks Canada prefers that no future egg collections occur in Wood Buffalo National Park due to concerns that egg removals may reduce the productivity of the whooping crane population and that more generally, human intervention and disturbance should be minimized. Boyce's research found, however, that taking one egg away actually increases the probability of nest success. His paper--co-authored by Subhash Lele from the U of A's mathematical and statistical sciences department as well as Brian Johns from the Canadian Wildlife Service-- is published in the December issue of Biological Conservation.
The last remaining whooping crane population nests in Wood Buffalo National Park and winters at the Aransas National Wildlife Refuge in Texas. At one point the bird's numbers reached a low of 16 in 1942 but the population has since increased to more than 200 birds. Not only has the Wood Buffalo-Aransas population been enhanced by the egg removal program but removing the eggs has allowed the establishment of additional populations like those in Wisconsin and Florida, and a sizable captive flock. Taken together, the benefits to the conservation of the species have been very substantial, said Boyce.
"Luckily, at the moment the program is so successful that there is no reason to collect more eggs," said Boyce. "But for Parks Canada to intervene with a formal policy to prohibit future egg collecting is inappropriate and flies in the face of the data, as we present in our paper."
Boyce suggests several reasons why a chick might survive when an egg is removed from a nest. Sibling aggression has been so strong that some chicks have been observed pecking the later-born bird to death. Also, a pair of chicks is more likely to attract the attention of a predator and parents can be more attentive if they only have a single chick to protect.
Even though long-term fitness is almost the same whether one egg or two is laid, the risk of extinction for the Wood Buffalo-Aransas whooping crane population is lowest when eggs are removed, says Boyce. He recognizes the need to minimize human influence in national parks, but says priority should be given to ensure persistence of threatened and endangered species so that diversity is not lost permanently. "Surely we cannot appreciate benefits to ecological-process management if components of the ecosystem are missing," said Boyce.
This research was supported by the Natural Sciences and Engineering Research Council of Canada and the Alberta Conservation Association.