Feather replacement or parental care? Migratory birds desert their offspring to molt

When parental care and the annual molt overlap in time, a migratory songbird often chooses single-parent desertion

Date:  April 19, 2018

Source:  American Ornithological Society Publications Office

A new study shows that when feather replacement and parental care overlap in time, migratory songbirds make a striking trade-off; they desert their offspring, leaving their mates to provide all remaining parental care.

This radical solution to conflict between parental care and the annual molt provides "a nice illustration of the complex lives that migratory songbirds lead," says Ron Mumme, the study's author and Professor of Biology at Allegheny College in northwestern Pennsylvania. "They have to negotiate conflicting demands and make difficult trade-offs and compromises, just like we do."

Migratory songbirds that breed in North America confront serious issues with time management. After spending a relatively leisurely winter and early spring luxuriating in warm tropical climates, they migrate north for a brief but highly eventful summer in North America, during which they must complete three energetically demanding and time-consuming tasks: (1) they must build nests, lay eggs, and provide for their offspring until the young reach independence, (2) they must completely replace all the feathers in their plumage as part of the annual molt, and (3) they must prepare for the fall southward migration by eating prodigiously and storing the body fat that will fuel their long-distance flights.

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Flying without wings: Losing feathers has a detrimental effect on migrating birds

Birds that moult at the wrong time of the year could be disadvantaged, according to a study by scientists at Lund University, Sweden. Birds depend on a full set of feathers for maximum efficiency when flying long distances, but the study shows that moulting has a detrimental effect on their flight performance.

The researchers trained a jackdaw to fly in a wind tunnel and measured different types of drag experienced by the bird. "We expected the bird not to be able to glide at the lowest speeds that it could glide at before moult and our results confirmed this", says Marco Klein Heerenbrink, who is involved in the research.

The results imply the bird could not fully compensate for the missing feathers during moult. This suggests that if a migratory bird departs prematurely before it has fully moulted, it is likely it will need more energy to make the journey and may need more stopovers too.

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Birds' scruffy feathers are only temporary

Some of the birds in your backyard may look unkempt if not downright scraggly, as though their clothes have worn out.

Birds, of course, are clothed in feathers, and feathers do wear out. The gorgeous, eye-catching plumage you saw in spring and for most of summer has begun to fade and look tattered from being bleached by sunlight, scraped against tree limbs and scarred by dust and gravel.

Think of the wear and tear on the feathers of a bird such as a western scrub-jay, which must continuously slip in and out of a nest placed deep within a tough-barked Hill Country shrub. Or a downy woodpecker in Southeast Texas that makes untold trips to a nest inside a tree hole excavated just underneath a vertically leaning limb.

Continued:  http://www.chron.com/life/article/Birds-scruffy-feathers-are-only-temporary-3865885.php