Studying molt in birds

Peter Pyle visited the Museum last week. Peter is considered one of the leading authorities on molt of North American birds. Molt is the process that birds go through to change and replace their feathers. It is essential to their survival and a major factor in their life cycles. There are multiple aspects to molt. Each year all birds go through one to several molts to replace feathers that if not molted would become too worn and broken down to be useful. Sometimes molt does not result in a change of appearance, but in many species molt is used to change the entire plumage coloration of a bird, like an adult male Indigo Bunting from its bright blue breeding plumage to a brown non-breeding plumage. This happens in the Fall; in the following Spring, the bird will go through another molt growing bright blue feathers for the next breeding season. Different species of birds have different patterns and complexities to their annual molts that have evolved to help them cope with the challenges they face annually. Breeding, migration, and non-breeding seasons have influenced the evolution of molt in birds in an amazing number of ways.

But there’s more, young birds start with downy feathers that they molt into a new set of feathers as they grow bigger. Many young birds take several years to mature and across this period they will have a number of different molts leading to distinctive non-adult plumages before finally molting into an adult plumage (and of course, they will continue molting this adult plumage annually throughout their lives).

This young male scale-backed antbird has some of the gray, black and white feathers of an adult, but he also has brown juvenile feathers as well.

How do we know all this?  Because researchers like Peter have spent thousands of hours in museum collections and in the field studying the molt patterns of individual birds so that they can understand the patterns in entire species.  Collections are essential places to study these patterns because there are series of specimens that have been collected throughout the year that can be directly compared to document patterns of molt. Peter's books ,Identification Guide to North American Birds, Parts 1 and 2, are the standard reference for describing molt patterns and aging many species of North American birds.  They are the bibles for researchers and bird banders studying the annual cycles,  movements, reproductive parameters and survival of North American birds.

So why was Peter working in our collection? This visit, he was gathering data for a project he is doing with a colleague Andy Engilis, Jr. (Curator of Museum of Wildlife and Fish Biology at the University of California, Davis) to document molt in birds of west-central Chile. This research is part of a National Science Foundation funded, long-term ecological project examining the abiotic and biotic factors that influence plant and vertebrate communities and will serve to launch a new era in avian research in Chile (the development of a means to interpret banding information to forward studies in Neotemperate bird migration and productivity studies). The Field Museum happens to have the best collection of Chilean birds in North America and one of the best in the world.  So Peter was able to study series of Chilean specimens in our collection of the species he is studying to learn about their molt patterns. If there were not Chilean specimens, he was often able to look at specimens we have of the study species from neighboring South American countries and get the information he sought on patterns and timing of molt that way. 

This is yet another example of how collections like ours provide important knowledge about the biology of birds. There is always something new to learn about molt, even in common birds like Indigo Buntings.  For instance, in 1986, using specimens from collections like ours, Sievert Rohwer, the long-time curator of birds at the Burke Museum of the University of Washington published a study in which he documented a previously unrecognized molt stage that Indigo Buntings go through annually.

While in Chicago, Peter also looked at specific specimens of ours for a number of other projects, including his work with his father on the Birds of Hawaii. Two of these specimens shed light on the historical importance of Field Museum collections. One was an 1836 specimen of Oahu ‘O’o (Moho apicalis), a species which went extinct, probably in the mid-1800s and a specimen that we received of White-fronted Goose which died after reaching the French Frigate Shoals (northwestern Hawaiian islands) in 1997. 

There is simply no end to the questions our collections can answer just about the subject of molt in birds.  After Peter left Chicago, he was going to do similar collection work at Harvard’s Museum of Comparative Zoology, Yale’s Peabody Museum, and the National Museum of Natural History (Smithsonian), where he will be able to look at different specimens there for his many projects. What is so important is that researchers like Peter can always come back again, when they can, with more questions and both old and new specimens and the data that make them so valuable will still be organized and waiting in the specimen cases of the Bird Division.