The Strange Case of Blue Jay Migration

Blue Jays have been a major presence in Eliza Howell Park during the last month, the time of their fall migration. Each year I anticipate their acorn harvesting frenzy (see “Blue Jays Harvesting Acorns,” August 27, 2018) and this year they again worked the oak trees in great numbers.

Note: All bird photos by Margaret Weber

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Their month-long period of intense activity in Detroit is exciting to observe, but I am increasingly aware of their unusual – and not fully understood – migration behavior.

Most birds that migrate through our area in the fall leave all or much of their breeding ground for the winter. Blue Jays, by contrast, are found in the very same areas all year round. It is interesting to compare the following two range maps. The first is White-throated Sparrow, also moving through here in September, and the second is Blue Jay. (These maps are taken from the Cornell Laboratory of Ornithology website.)

White-throated Sparrow range

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White-throated Sparrows leave almost their entire breeding area in the fall.

Blue Jay range

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Blue Jays are found throughout winter in the very same areas in which they breed. A few scatter to the west, but the entire breeding area remains occupied.

Such a range map usually suggests that a species is non-migratory. Blue Jays, however, migrate and do so in great numbers. Every fall the raptor counters at the two locations by Lake Erie (Detroit River Hawk Watch at Lake Erie MetroPark and Holiday Beach Conservation Area in Amherstburg, Ontario) count Blue Jays as well as raptors. As of October 10 this year, Holiday Beach watchers had reported over 350,000 Blue Jays moving through since early September. And the migration wasn’t fully over yet.

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This is what is known (and/or thought likely) about Blue Jay migration, based on my review of some of the published research:

  • The species is partially migratory; only some migrate
  • Most that migrate go only a few hundred miles south in the fall
  • It is estimated that fewer than half migrate
  • Those that migrate (and those that don’t) include both young birds and older birds
  • Individual birds might migrate one year and not the next and then migrate again in the following year
  • The migration number in a particular year is suspected to be related to food sources

The jay numbers will soon decline in Eliza Howell as the migrants move on. But I do not know whether individual birds like this one, seen in an oak tree in September, will stay for the winter.

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I do not know whether this one, nesting here in June, will be around in the coming winter

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I had assumed, if I thought about it much at all in the past, that the same birds (the non-migrants) were present in summer and winter and the migrants all passed through. Now I doubt that.

One of my other questions, not addressed in the limited research I have reviewed, is whether some of the individual jays harvesting acorns in the park leave/migrate before the winter and do not ever go back to eat the acorns they hid. Is acorn harvesting possibly community and not just individual food-gathering?

The Blue Jay is a common bird, so it is tempting not to give it a second thought. But I rarely see jays these days without thinking about what I do not know about them.

Four Months Here, then Gone Again

Among the birds that breed in Eliza Howell Park and “winter” in or near Central America, I selected four and reviewed my records on first sighting and last sighting in the park each year from 2010 to 2018 (9 years). The dates indicate clearly that they are only short-term residents here, coming to breed, and longer-term residents elsewhere.

Note: All photos by Margaret Weber

Baltimore Oriole

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I do not get to the park every day and, of course, I miss some birds when I am present. Nevertheless, the record is quite consistent. Based on this experience, I expect to see the first Baltimore Orioles of the year the first week of May and will probably not see them after the first week of September.

Baltimore Oriole 2010 – 2018

First seen:     5/6    5/8   5/2   5/5   5/6   5/6   5/7    5/1    5/4

Last seen:     9/3   8/25  9/5  8/22  9/7   9/7  9/11   9/4   9/3

By the end of May, I start finding Baltimore Oriole nests every year in the large trees, often near the road, and find a total of five in a typical year.

Barn Swallow  

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Barn Swallows also nest in the park every year, at least one pair under a shelter and several under the Fenkell Avenue bridge over the Rouge River.

Barn Swallow   2010 – 2018

Fist seen:   4/24  4/23  4/19  5/1   4/17   4/26   4/22  4/29  4/25

Last seen:   9/2  8/28   8/24  8/22  8/24  8/23  8/20    9/9   8/31

Blue-gray Gnatcatcher

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The Blue-gray Gnatcatcher arrival date (more exact, first sighting date) is spread over a three week period, not as consistent as with the Baltimore Oriole. The last-sighting date covers a shorter range of time. By the end of the second week of September, they have started their trip back to Central America (some to Florida) for a longer stay.

A couple pairs of gnatcatchers always nest in Eliza Howell and I have been successful most years in locating a nest to point out to participants in the June Detroit Audubon breeding bird field trip.

Blue-gray Gnatcatcher 2010 – 2018

First seen: 5/3  4/28  4/19  5/1  4/23  4/11  5/1  4/20  4/28

Last seen:  9/6  9/14   9/9   9/2   9/7   9/7   9/11   9/4   9/5

Ruby-throated Hummingbird

male ruby throated protrait

There are always a small number of Ruby-throated Hummingbirds that spend four month at Eliza Howell, but I have found an actual nest only once over these years. I am quite sure they nest here every year, however, based on the behavior of adults and on the slight increase in numbers by late summer. They spend the non-breeding months in Central America.

Ruby-throated Hummingbird 2010 – 2018

First seen: 5/12  5/8   5/10  5/14  5/10   5/15  5/13  5/11  5/4

Last seen:  9/6   9/5    9/9    9/14  9/14  9/13   9/16   9/9   9/22

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These four species are not the only birds that nest in the park and leave after breeding season, but these records may be sufficient for now.

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There are several points to be made based on the above records.

  1. Birds that migrate are amazingly consistent from year to year. It is often possible to predict when (within a week or so) a particular species will show up again.
  2. If someone wants to see any of these four species in October, don’t come to Eliza Howell.
  3. This information, along with the annual fly-through of the warblers, helps to explain why many bird watchers in this part of the country go a little crazy as May approaches. By then, it will have been a long time that some favorites have been gone.