Every wildlife reintroduction depends on numbers. The more animals you can release into the wild, the better the odds are that some will survive to breed. That is especially true for long-lived, slow to reproduce species like Whooping cranes. Since we moved to White River Marsh in 2011 it has been challenging to build up this population for a number of reasons.
Stochastic resilience is a term researchers use to describe the ability of a population to overcome the random occurrences that, from time-to-time, put pressure on the survival of a species.
This past spring is an example of the environmental pressure that both Whooping cranes and Sandhills had to tolerate. Above freezing temperatures in March allowed many cranes to begin nesting but a prolonged and heavy snowfall in April caused the abandonment of at least some of those nests. After the snow we were back to seasonal weather and the cranes started the second round of nesting – just in time for record rains to raise water levels and flood many nests throughout central Wisconsin.
We are currently studying the reproductive success in Sandhill cranes in hopes of determining how suitable this environment is for the Whooping cranes we are working so hard to reintroduce. At the same time we are releasing a few parent-reared Whooping cranes but the odds are stacked much higher for the latter.
So far, we have located a dozen or so Sandhill nests and radio-tagged a handful of chicks. We know there were more nests out there that we couldn’t locate but eventually the resulting chicks will get bigger and their parents will lead them out into the open where we will have another opportunity to add them to this study.
By comparison, there are only four potential Whooping crane pairs in the area that might have bred this year. We hoped that 5-12 and 67-15 (F) would nest somewhere close to the pen site but they are hard to see and often appear together or flying when they are tracked. Normally during incubation, one would be on the nest while the other is off foraging in a field nearby. It is possible cranes 4-13 and 10-15 (F) are nesting in Germania Marsh west of White River, but again, they are too deep in the wetland to see. Both of those females are only three years old so successful breeding would be an anomaly.
Whooping cranes 10-11 and 27-14 (F) nested at the Grand River Marsh, which is part of the White River complex. Their first nest was flooded out by the high water but they are nesting again and we have our fingers crossed. She is four years old so her chances or better but they are normally five or six before they are successful at producing a chick.
Numbers 4-12 and 3-14 (F), known locally as the Royal Couple, nested deep in the marsh this year. So deep in fact, that we can’t get in there to check on them or even see them from our live camera perched thirty feet in the air. They were last seen together foraging near the Crane Camera on May 3, and thereafter, only one-at-a-time was spotted foraging up until May 31st. Since then, we haven’t seen either of them in their favorite foraging field.
We have aerial shots of the nest and Bev Paulan was able to confirm two eggs. Heather predicted they would hatch on or around May 30th and we know they were still incubating, or possibly brooding, on May 27th. But by May 31st, the nest was empty and they were nowhere to be seen.
It’s all very disappointing but to be expected. They are still young and need to learn by trial and error how to deal with predators, weather events and all the other threats that wildlife encounter daily.
All of these variables are considered when a population viability analysis (PVA) is done to predict whether a species will survive into the future. When there are lots of them around as in the case of Sandhills, the population can still grow, albeit slowly, went they endure a spring like this past one. But when the numbers are low like the four pairs of Whooping cranes around White River, a few losses make a big difference.
We must remember that this entire recovery effort started with only fifteen individuals and if nothing else, Whooping cranes are tenacious.