It is estimated that it takes between 80 to 100 days for a Whooping crane to grow large and strong enough to fly. It seems surprising that a term like ‘estimated’ would be used for a species so widely researched… not to mention an evaluation that allows almost a month of latitude. Still it is a hard question to answer when the determining factors are as diverse as weather, geography, vegetation, physiology and nutrition.
Anyone who has watched our camera knows there is a substantial difference in the size of our chicks and it is not always governed by gender or age. Some birds are just smaller or slower to develop than others. In the wild, nutrition may play a role in that development but our birds get a balanced diet that is not dependent on the abundance of natural food or how good they are at foraging. The better their nutrition, the faster they can develop the muscles needed to fly. Proper and adequate nutrition can also ensure strong and flawless feathers.
Weather could also affect their progress from egg to airborne. Wings, whether they are made of feathers, fabric or fiberglass must all pass through the air in order to generate lift. When you are faced into the wind, some of that air is already moving over your wings even before you start adding your won energy to the process. That means it takes less effort to take off into the wind.
If you have watched the crew trying to encourage the chicks to fly by running up and down the runway, it is obvious that they prefer to go into the wind. That is one of the first, and most important, flying lessons learned by birds – and pilots. Breezy conditions, especially in the morning, inspire young birds to spread their immature wings and run/flap into the wind. That exercise helps to develop muscles and balance well before they are ready to lift off.
Vegetation and geography can also factor into how soon they fledge. Whooping cranes generally take a few steps to get airborne. Mature cranes can lift off vertically when needed but that takes strength and experience. Fledglings start by running, which evolves into elongated steps and then short hops as the load is progressively transferred from their feet to their feathers. For young cranes, their early takeoff runs may be as long as fifty feet. That kind of open environment might be hard to find in tall, marsh vegetation or open water.
That’s the primary reason we keep the old runway cut. It allows the birds to get a running start and even while they are too young to actually leave the ground, it develops their muscles and teaches balance.
There is a phase of flight called ground effect that has to do with induced drag and the proximity to the surface but it simple terms, it means that it is easier to fly within a few feet of the ground than it is at higher altitudes. You may have noticed the birds flying the length of the runway at a few feet up and stopping at the far end. Most wild birds don’t have the advantage of an open flat runway unless their parents led them to feed in a harvested agriculture field. Keeping the runway cut, gives the costume reared chicks an early start at flying.
The other problem in determining how long it takes Whooping cranes to learn to fly is figuring out when they have it mastered. You could say they are flying when they are a foot or two off the runway but that does not mean they could fly across the marsh with their parents to feed. In the past, we suggested the flock was fledged when we recorded the youngest bird making a full circuit around the pen area. Using those criteria, we estimated (there’s that word again) that the birds we raised over 15 years, fledged at an average age of 94 days on August 12th. This year’s cohort fledged on July 30th at an average of 91 days. Admittedly, that’s a broad evaluation so let’s leave it between 80 and a hundred days.