Crane social structure is based in the family.
The fundamental unit of crane social structure is a "nuclear family" - two parents and one or two colts. The adults have a working partnership. Both help make the nest, incubate the eggs, and educate their young.
Young colts migrate south in the family unit, over-winter with their parents, and are commonly seen with parents at spring staging areas like along the Platte River in Nebraska. Colts become independent as they complete their first full migration. In the seven times that Millie and Roy migrated south with their colt in the fall, the colt was absent on their return next spring.
Pair bonds endure for decades.
Cranes establish pair bonds in their second or third years1 and the two individuals remain together throughout the year. Unison calling, purring, dancing, and perhaps pheromones, nourish the tight pair bond. Usually the pair bond persists as long as both cranes survive, which can be 20-30 years.
When one partner dies, the behavior of the surviving spouse is consistent with an underlying emotion of bird grief.
If nesting attempts are runsuccessful, divorce may follow. Dr. Bernhard Wessling used sonograms of crane calls to identify individual call signatures that distinguish particular European cranes in a marshland near Hamburg, Germany. Except for one case of divorce, the pairs stayed together and tended to nest in the same territories from 1997 through 2004. In Florida ssandhill cranes, finding a new partner is common after divorce or death of one of the pair1.
Are cranes neighborly?
Site and mate fidelity are legendary among cranes. On the basis of photographs, body language, unison calls, and behavior, Millie and Roy are the same cranes we have watched since 1995.
We often hear Millie and Roy unison calling and being answered by other cranes in the valley, probably from ponds that are a few kilometers from each other. If Roy and Millie's calls are not reciprocated, Roy may fly off, apparently to investigate. We suspect that these conversations might be more than territorial defense. The Goldsteam crane community may have social structure. The crane calls we hear in Goldstream Valley suggest a similar cluster of territories but we lack enough data to know if the neighborhood is stable from year to year.=========
SA Nesbitt, MJ Folk, ST Schwikert, & JA Schmidt, 2001. Aspects of reproduction and pair bonds in Florida sandhill cranes. Proceedings North American Crane Workshop 8:31-35.
• 2 - First week
• 3 - Incubation
• 4 - Roy's ice dancing
• 5 - Pi hatches
• 6 - Pi dances
• 7 - Dodging Danger
• 8 - Dragonflies
• 9 - Fitness for flight
• 10 - Swim with Dad
• 11 - Dance and fly
• 12 - August flight school
• 13 - Foraging and intruders
• 14 - Pi explores his world
• 15- -Time to migrate