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For most Purple Martin pairs, migration means parting ways

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Purple Martin at Daniel Webster Wildlife Sanctuary, Marshfield, Massachusetts, by Christopher Ciccone.

Despite the many insights into bird migration gained in recent years, one simple question has gone unanswered: Do paired birds associate more closely on migration than non-paired birds?

Scientists suspect that when pair members fly south separately, or when they spend the winter in separate locations that are ecologically dissimilar, divorce is likely. But, in fact, little is known about what happens when mated pairs make their migrations.

To address this, Bridget Stutchbury, of York University, and colleagues from the University of Manitoba and the Purple Martin Conservation Association attached light-level geolocators to Purple Martins at breeding sites in North America between 2007 and 2014. Then, after the birds returned, the researchers compared data from members of mated pairs with information from randomly selected nonpaired males and females.

See reader photos of Purple Martin.

Martins typically make one or two prolonged stopovers in the Yucatan Peninsula or Central America during their annual fall migrations between eastern North America and the northwestern Amazon. Stutchbury and her team documented when the martins migrated, when and where they made stopovers, and where they spent the winter.

In 6 of 12 instances in which both pair members showed up the following year, males and females started their autumn migration within four days of each other, but the pair members rarely occupied nearby stopover sites, and they were separated by an average of 560 km, about 350 miles, upon arrival at the winter grounds, in Brazil. Members of only one of the 12 pairs arrived at their winter roosts within five days of each other. What’s more, in 10 of the 12 cases, males not only departed from Brazil before their former mates but also arrived at their breeding sites, on average, 13 days earlier.

“The strong mismatch in spring migration schedules of formerly paired birds documented here, with arrival of former pairs separated by almost two weeks, may make re-pairing unlikely even when both pair members survive migration,” Stutchbury concluded.

Read the abstract

Bridget J. M. Stutchbury, Kevin C. Fraser, Cassandra Silverio, Patrick Kramer, Bob Aeppli, Nanette Mickle, Myrna Pearman, Anne Savage, and James Mejeur (2016) Tracking Mated Pairs in a Long-Distance Migratory Songbird: Migration Schedules Are Not Synchronized within Pairs, Animal Behaviour, 114: 63-68. Abstract.

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