In what is probably the most awww-inducing story of the week, researchers have confirmed that whooping cranes mate for life, often starting their relationship as childhood sweethearts. Courting begins early and the couple spends a whole year (if not more) building a friendship before breeding, according to a new study published in the December issue of Animal Behaviour.
The fact that cranes – like many birds – form long-term monogamous partnerships is not in itself breaking news, but the formation of these couplings has been under-studied and many researchers have (wrongly) assumed relationships develop shortly before first breeding. This appears to be the first time ecologists have examined the entire life history of a migratory population of whooping cranes and analyzed the relationship between couples before breeding begins.
Claire Teitelbaum, a PhD student from the University of Georgia in Athens, Greece, and co-workers followed a group of whooping cranes that had been reintroduced into the eastern United States back in 2001, fitting each bird with a unique leg band and a transmitter. In total, there were 89 individuals who, over the course of the study, forged 58 partnerships.
The majority of these partnerships (62 percent) began associating a year or more before breeding together. And while courting usually lasted between 11 and 12 months, there were 16 cases (28 percent) where it lasted two years or more. There was at least one report of a pair who spent a long 4.5 years getting to know one another before breeding.
Another interesting observation – 60 percent of couples began associating before at least one of the pair had reached sexual maturity, which happens when a bird is around three years old. This seems to suggest that there is some social advantage to finding a mate earlier rather than later. Previous research has shown that survival rates are higher among paired up birds and that an early-life match can help cranes achieve a more dominant status.
But these couplings are not entirely without a hitch. In fact, much like human relationships, they can end in divorce. The researchers noted seven separations during the study. In four cases, both individuals were able to find another partner. In the remaining three, only the females entered a second relationship. There were also 13 examples of a widowed-bird forming another partnership.
We'll have to wait and see how common this behavior is across the bird population as a whole but it does show that whooping cranes pick their partners very, very carefully. And it's probably just as well because they spend over 70 percent of their time together.