Preventing Bird Divorce: Mates Take Different Flights, Arrive Together
A shorebird named the black-tailed godwit presents a puzzle to biologists: “arrival synchrony” (leave it to scientists to give big names to simple concepts). The males and females of this bird mate for life, but like some humans, live apart for months at a time. This presents two puzzles: how do they stay apart without getting divorced, and how do they arrive together for the summer fling when they take different routes to the destination? Some birds migrate together; others stagger their take-off and landing. But the faithful black-tailed godwits winter in different areas averaging 955 km apart, yet somehow find a way synchronize their migrations to arrive within 3 days of one another. This remarkable synchronization shows that “The mechanisms required to achieve this synchrony and prevent ‘divorce’ illustrate the complexity of migratory systems,” write four UK biologists publishing in Nature:1
Long-lived migratory birds generally show high degrees of mate fidelity, and divorce is often followed by a decrease in reproductive success. Synchrony in timing of arrival on the breeding grounds is thought to be crucial for retaining a mate from the previous year and avoiding a costly divorce….
How is this degree of synchrony maintained between pairs when they winter so far apart and the environmental conditions for migration are likely to differ locally? It is possible that pairs of birds may winter in areas of similar quality (despite their geographic separation) and so be in a similar condition to arrive at specific times in spring; or they may share some genetic or physiological determinant of timing of migration; or they may independently synchronize their arrival to the optimal time for each specific breeding location (for example, to exploit peaks in resource abundance). As individuals often use a series of passage sites during spring migration, they may refine these timings as they approach their breeding grounds. Identifying which of these mechanisms is operating is likely to be key to understanding how synchrony is achieved and divorce avoided in migratory species.
Thus they leave it an unsolved puzzle, and offer no explanation for how the chicks learn this by their first anniversary, or what form the “genetic or physiological determinant” might take that could explain another wonder of nature.
1Gunnarsson et al., “Pair bonds: Arrival synchrony in migratory birds,” Brief communications, Nature 431, 646 (07 October 2004); doi:10.1038/431646a.
Humans can learn some things from birds. Does absence make the heart grow fonder, or does absence make the heart go wander? Somehow these godwits are able to maintain remote relationships and stay faithful (although “faithful” has no moral meaning to a bird). (Notice that divorce is costly to birds, too, even without lawyers.) More amazing is how they can synchronize their arrivals without a long-distance phone call and Priceline.com. Do they plan ahead and communicate their schedules with loving chirps? How can they even find one another after landing, among all the other couples, when they all look alike? There are still lots of puzzles out there for naturalists. Just don’t bore us with another evolutionary just-so story. This bird apparently was given some kind of God wit.