Songbird student pilots delay departure and make frequent stopovers during first migration

Aug 20, 2014
A close-up of a wood thrush. Credit: Kevin Fraser

Juvenile songbirds on spring migration travel from overwintering sites in the tropics to breeding destinations thousands of kilometres away with no prior experience to guide them. Now, a new study out of York University has tracked these "student pilots" on their first long-haul flight and found significant differences between the timing of juvenile migration and that of experienced adults.

"Juveniles departed later from their overwinter sites in Belize and Costa Rica relative to , and they became progressively later as they moved northwards because they stopped for more days," says York U researcher Emily McKinnon, the study's lead author. "By the time they arrived at they were almost 2 weeks behind the adults, and overall their migration took 50 per cent longer in terms of days spent traveling."

The study, published today in PLOS ONE, tracked juvenile wood thrushes from Belize and Costa Rica all the way up into the US and Canada. The birds were fitted with tiny geolocator "backpacks" to track their route, and researchers found that even though the juvenile birds took 50 per cent longer to reach their destination, they travelled a similar migration path as their adult counterparts, including the dangerous open-water crossing of the Gulf of Mexico – a non-stop flight covering 1000km.

To find out why the young birds were departing at a later time than the adult wood thrushes, researchers compared the health of young birds and adults in late winter in Belize before they departed on migration.

A wood thrush caught during Belize fieldwork. Credit: Kevin Fraser

"We found no age-related differences in the condition of the birds, although had shorter wings, which could lead to less efficient flight," says study co-author Kevin Fraser. "We think the big differences we found in spring migration timing might be a result of an age-related genetic program. If you are an inexperienced young bird, it could actually be better to arrive later at breeding sites if you can't compete with the adults for territories. Juvenile birds' late migration could have evolved to help them avoid the worst of the competition for breeding sites in early spring and arrive after the dust has settled and the adults have claimed the best territories. Why risk arriving early if you can't compete with the adults anyway?"

The researchers say these findings are the first step towards understanding the "black box" of juvenile songbird migration, and point to the dangers that are inherent in a songbird's first migratory flight.

A wood thrush with a geolocator caught during Belize fieldwork. Credit: Kevin Fraser

"Our findings illuminate a little studied part of the life cycle of migratory birds – the development of spring migration behaviour – that has never been examined in the wild before," says McKinnon. "The 50 per cent longer migration duration for juveniles, combined with a greater number of stopover sites, puts this age class at higher risk of mortality. Since the wood thrush is a threatened species in Canada, and declining throughout its range, a good step in conserving this species would be to identify and protect spring migration stopover sites."

Explore further: Researchers use bird 'backpacks' to put wood thrushes migration on the map

Related Stories

Study provides insights into birds' migration routes

Jul 21, 2014

By tracking hybrids between songbird species, investigators have found that migration routes are under genetic control and could be preventing interbreeding. The research, which is published in Ecology Le ...

Environmental conditions may impact bird migration

May 14, 2014

Wind conditions during spring migration may be a predictor of apparent annual survival and the timing of breeding in yellow warblers, according to results published May 14, 2014, in the open access journal PLOS ONE by Ann ...

Recommended for you

Do you have the time? Flies sure do

10 hours ago

Flies might be smarter than you think. According to research reported in the Cell Press journal Current Biology on May 28, fruit flies know what time of day it is. What's more, the insects can learn to con ...

Barking characterizes dogs as voice characterizes people

13 hours ago

An international group of researchers has conducted a study on canine behavior showing that gender, age, context and individual recognition can be identified with a high percentage of success through statistical ...

Bird beaks feeling the heat of climate change, say scientists

15 hours ago

While the human population grapples with ways to counter the effects of climate change, Deakin University research has discovered that birds might have been working on their own solution for the past 145 years – grow bigger ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.