This video may look like it’s about dancing cranes and clearly that is what these two cranes are doing, and this is a great demonstration of that behavior, but my purpose in showing it is to talk about something else. Look at the two birds, particularly the second one and notice the difference, notice what’s missing – his black primary feathers and less obvious also the white secondary feathers. This bird has molted all of his flight feathers and while he can jump and dance he cannot fly without those feathers.
Cranes, like all birds, periodically molt their feathers; in other words they shed or lose their old feathers and replace them with new ones. Although birds spend a lot of time preening and maintaining their feathers eventually they get worn out and have to be replaced. Different species have evolved with different strategies on how this occurs and even within the crane family there are differences. Some birds like the whooping crane lose all their flight feathers at one time and are rendered flightless until the new feathers have grown in, while other birds only replace a few feathers at a time and thus always retain the ability to fly. If you’re a bird one of your best defenses against a predator is the ability to fly away so losing all your flight feathers and being ‘stuck’ on the ground seems like a bad idea, and truly it is a dangerous time for a bird, but there are many species that undergo this synchronous molt of all their flight feathers. Within the crane family 10 of the 15 species (Whooping Crane, Blue Crane, Wattled Crane, Red-Crowned Crane, Siberian Crane, White-Naped Crane, Hooded Crane, Sarus Crane, Black-Necked Crane, and Eurasian Crane) undergo this synchronous molt and the remaining 5 species (Sandhill Crane, Black-Crowned Crane, Gray-Crowned Crane, Demoiselle Crane, and Brolga Crane) undergo an annual partial molt and therefore always retain the ability to fly.
A lot of what we know about molting in cranes, and whooping cranes in particular, is from observations of birds in captivity and also from observations of birds from reintroduced populations, as the wild whooping cranes are generally only observed from the air in the very remote Wood-Buffalo National Park. Whooping cranes typically become very shy and secretive when they are molting and unlike the bird in the video they often don’t even open their wings, seemingly not wanting to ‘show’ the missing feathers. Whooping cranes typically undergo their first molt at age 2 or 3 and then every second or third year after that and it takes ~6 weeks for the new feathers to grow in so the cranes must pick a safe location to remain in during this very vulnerable time.
This spring we were a bit surprised to see a number of our 2 year-old birds moving around, leaving their usual locations, and in fact at one point 8 of them came back to the White Lake (WLWCA) marsh, to the refuge where they were originally released. While a great location for the cranes it is harder for us to monitor them out there so we rely more on the data from the birds’ GPS transmitters. Unfortunately some of the transmitters starting missing transmissions which can be a cause for concern so I decided to take a boat out into the refuge to try and get a look at them. Luckily many of the birds that were in the refuge also have a VHF transmitter so I could actually track them in addition to searching in the location of their last known GPS point.
On 10 June, Wayne Sweeney, administrative manager of WLWCA, and I went out in an airboat in search of these cranes. Wayne is an excellent airboat operator and having worked at WLWCA for years, knows the area very well so we headed out to the general area and stopped periodically to listen to the signals and fine tune the direction of our search. The birds were divided in several groups and we first searched for and found a pair that flew off away from us. Next we searched for what I was expecting to be a group of 4 birds but when Wayne first spotted them there were only 3 and as he pointed them out to me we saw that they were running away from us even though we were still quite far from them. It took me a second to process what I saw – they were running away as opposed to flying away from us and as they continued running toward taller, thicker vegetation I got a quick glimpse of them through my binoculars as they opened their wings while running and I was able to confirm what the running first indicated – these birds were molting, they had no flight feathers, only an inch or two of new blood feathers growing in. Not wanting to disturb those birds any further we moved on to search for the other bird that had previously been with those 3. As we tracked her signal and got closer we finally got a quick glimpse of her running away into taller vegetation; we didn’t see her open her wings but her behavior indicated she was also molting.
So now knowing we had 4 birds molting I spent a good deal of time over the next week and a half tracking and checking on the other 2011 birds trying to confirm their status and found an additional group of 3 that were molting. They had moved to a larger, more remote rice field from where they normally spent their time which alone wouldn’t have been confirmation of them molting but luckily I was able to catch quick glimpses of each of them stretching or flapping their wings and see that they too were growing in new feathers. That brought the total of molting birds up to 7 and through observations of the remaining 5 2011 birds I was able to confirm that they were not molting.
This was a dangerous and vulnerable time for the birds but they had moved to good, safe locations, yet I couldn’t help but remain a bit uneasy over the next few weeks and made sure to check on the birds each week to see how they were doing. Based on the GPS data from the transmitters and from when I first confirmed that the birds had molted I had an estimate of when I thought they should be flying again and was happy and relieved when that day finally came. It was also very interesting to see that shortly after the birds could fly again they all moved back to the locations they normally stayed at, the ones they had been at prior to molting.
Having gained data on molting this year I’ll know better when to look for it next year and I expect the 5 two-year olds who didn’t molt this year will likely molt in addition to some of the 2012 birds who will be 2 next year.
I was never able to get a photo of any of our molting birds showing their wings with the missing feathers or the new ones growing in so I was glad when my friend and colleague, Eva Szyszkoski, sent me this video that had been taken by an ICF intern, Henrietta, of a pair of whooping cranes in WI and I am grateful to them for letting us use and post the video.
Update written by Sara Zimorski