The Hidden Migration

​As we enter June, birds from here all the way to the Arctic are starting to nest or are already raising young. Migration, a phenomenon that starts in February with raptors and waterfowl, ends in early June with the last of the landbirds and shorebirds heading north through the mid-continent. 

​For many, now is a transition time of changing from migrant birds to those breeding, and even switching to non-avian interests such as butterflies or dragonflies. For others, it is a time to reflect on the past few months of excitement and dream of the great southward migration of fall.

​But there is a unique migration that is ramping up in late May and will be gone by mid-June. It is a migration that goes unrecognized by most, even though it is so obvious around them. A migration that is part of the life cycle of many species of bird and is of evolutionary significance to their survival. While exhibited by many species, maybe the best example of this migration in the mid-continent region of North America is that taken on by a bird thought to be extinct as little as 75 years ago but is one of today’s most recognized birds: the Giant Canada Goose, the Canada Goose subspecies of temperate North America.

​This unseen, or at least unrecognized, migration by this common species is the Molt Migration of non-breeding individuals. Most people that have been out and about over the last couple of weeks may have noticed the flocks of geese that seem to have materialized out of thin air. We have seen the pairs defiantly raising broods since late April, so where have these new flocks come from and why did they become suddenly abundant? 

A flock of molt migrant geese heading to the fields to feed as they stage in the Lake Erie Marsh Region in preparation for heading to more northern destinations.

​These are the two-year-olds (birds hatched last calendar year) with a few failed breeders mixed in. The Giant Canada Goose does not breed until three years old in most cases. In an evolutionary sense, these individuals could become a burden on the breeders of their species and compete for food resources against growing youngsters. So, it is in the best interest of the species, or in this case the subspecies, for these individuals to leave the breeding grounds and travel elsewhere for the important “summer molt” period. That is what these flocks of geese represent. This “cohort” of the population is staging in preparation to migrate north to molt. So they will disappear and we Midwesterners will be back to just pairs and rapidly growing goslings passing through their own ugly duckling stage. 

​The end points of this molt migration are as traditional as the more known spring and fall grand migrations taken on by a host of species. Just as a Bald Eagle, Pectoral Sandpiper, Common Loon, Blackpoll Warbler, Song Sparrow, hen Northern Pintail, or Interior Canada Goose return to their breeding grounds, these molt migrant Giants repeatedly return to their population’s ancestral molting grounds (Teaser: notice I said hen Pintail; some cool things go on with ducks that are very different than geese and play a major role with speciation and sub-speciation, but that’s a story for another time).

Auxiliary markers such as neck collars have been utilized to obtain resightings of birds without having to capture them again. This Ohio Giant Canada Goose is wearing a white neck collar that was useful in gathering movement data of Ohio-hatched birds.

​From band recoveries and, even more importantly, from additional auxiliary markers such as neck collars and radio transmitters, we have determined some of these traditional molt destinations. It can be very specific and fascinating. For Ohio, Giant Canadas raised in the central portion of the state (influenced by the Killdeer Plains Wildlife Area population) have the west shore of James Bay as the dominant summer molt destination. To the Ohio Giant population, it is immaterial that this happens to be the breeding grounds for the Southern James Bay population of the Interior Canada Goose. To the Interior, it’s potentially a different story, especially if habitat loss reaches the subarctic and competition becomes a problem.

Molt migrant Canada Geese from midwestern states were encountered throughout the James Bay lowlands during banding operations of the Interior Canada Goose populations that breed in this subarctic region.

​Northeast Ohio Giants head to the… northeast, causing some of Toronto’s headaches of fouled beaches and the like. Mercer County-influenced populations from western Ohio seem to home into the western shore of Hudson Bay and into Manitoba Province. The Lake Erie Marsh region population of Magee and Ottawa NWR is a bit of a mystery as no large concentration has been discovered, but perhaps they cover the landscape of northern portions of Ontario. Michigan studies indicated a movement from breeding grounds in Michigan to the Ungava Peninsula of Quebec where James and Hudson Bays link. Regardless, come October and November, these molt migrants will return to their home breeding areas to begin the next phase of their lives.

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​If nature isn’t fascinating enough, the Giant Canada Goose is just one example of a myriad of stories on how birds and all wildlife cope with survival both day-to-day and through generations. This is just scratching the surface of “Molt Migration” as it represents the strategy by delayed breeding species. Another form of “Molt Migration” occurs in species where the male takes little part in raising the young (ducks, for example). After breeding with the female, behavior and hormones slowly change in the male, often triggering a molt migration to a far-off land to go through the drastic molt that ducks endure each summer where they become flightless for a period as new flight feathers grow. Again, through molt migration, they cease to be a burden on the female and growing youngsters. Examples in northwest Ohio are the large flocks of male Mallards that migrate in late summer to the Lake Erie Marsh Region annually to molt. Another example is large flocks of Northern Pintail males that move to the shores of James Bay to molt, a long way from the prairies where they breed.

​SO, now when you see those flocks of Canada Geese in late May, think and dream about what far-off lands they will soon be heading to to retire last year’s coat of feathers. Birds are so fascinating in so many ways!