They Leave…

Violet-green Swallow, a summer visitor to my yard.

“To all of you who, like me, have become bird watchers during these months of sheltering in place, I’ve got some bad news: They leave.”

The article in the Democrat & Chronicle, a Rochester NY newspaper, continued with author and new birder Jim Memmott complaining that he has “fed them, adored them, and photographed them endlessly” only to have his backyard birds migrate. As he explains, he’s dealing with abandonment issues.

I highly recommend the article—it made me smile as I identified with his disappointment over the disappearance of so many birds, at least for the winter.

The birds are leaving Colorado, too. On a recent birding outing to a nearby mountain lake, I realized that there was a reason for the quiet stillness—many birds had headed south to their winter homes. No Soras or Virginia Rails, no American White Pelicans. I especially missed the swallows that had spent their summer soaring over the water nabbing midges, mosquitos, and other snacks. A few stragglers—Wilson’s (below, left) and Yellow-rumped Warblers—were stuffing themselves on insects as they worked their way southward. Another week and they’ll be gone too.

I’ve long wondered exactly what triggers the instinct to migrate. Ornithologists still don’t know all the answers, but it’s currently believed to be a combination of factors. Day length surely plays one part, first telling the birds to lay on some extra weight to sustain the rigors of prolonged flight, then sending them off on their journey.

Genetics matter too, and likely define why some birds, such as Rufous Hummingbirds, migrate in July or August, as soon as they’re done nesting, while others, such as many warblers, wait until now, in mid-autumn. Even migratory birds confined, indoors where temperature and day length are constant, get antsy each spring and fall, constantly fluttering to one side of the cage.

Rufous Hummingbird

Cooling temperatures matter, too, although the low of 21 we had on September 8 should have sent every bird packing.

And while birds migrate to take advantage of season food resources, It’s more than just the availability of food. Leaving feeders up doesn’t cause birds to stick around when they should be on the move. Rather, providing readily available calories helps fuel their migration.

When we think of migration, we tend to picture birds such as Swainson’s Hawk (below, left), which we see here in Colorado during the warm months, dining on grasshoppers and small mammals. The hawks head for the pampas of Argentina when the northern hemisphere chills, in search for an endless summer. The Arctic Tern takes it a step farther, flying from pole to pole on a year-long rotation. It’s hard to imagine that the birds I saw in Alaska one June would be hanging out around Antarctica come January!

But not all birds fly so far. The Mountain Bluebirds (above, right)we enjoy in Colorado over the summer merely move a few hundred miles to New Mexico, where there is an abundance of juniper berries to tide them over the winter.

It’s hard to tell that some species migrate. American Robins and Canada Geese, to name two, are present in Colorado all year long. However, the birds we see during the summer aren’t the same individuals we find in winter. Instead, the entire population shifts back and forth. Montana’s summer geese winter in Colorado, while those that were here in July are found in New Mexico come December.

Canada Geese

Not all migratory routes run north and south. In my recent post about Haystack Rock, I mentioned that we missed seeing the Tufted Puffins that nest there by a mere three days. They’re gone by mid-August, returning to the open ocean and not returning to shore until the following May. These birds don’t go north or south so much as back and forth—to land for nesting, then out to sea to feed the rest of the time. The Marbled Murrelet spends so much time at sea that no one could figure out where they laid their eggs. The location of their nesting sites baffled scientists for decades until it was finally discovered (in 1974) that they breed on shore, high in the canopy of old-growth redwood forests.

Dark-eyed Juncos (below, left) are an example of a species that migrates vertically. The juncos move to higher elevations for the summer, then reappear in my backyard come late fall. When you think about it, there’s not much difference between the arctic tundra and the tundra that exists above the tree line farther south. Prairie Falcons (below, right top) and American Dippers (below, right bottom) are two more examples. In all, 116 North American bird species migrate via a change elevation rather than latitude.

I’m always sad to see our summer visitors depart, but winter brings a new group of species to enjoy. Rough-legged Hawks arrive from their breeding grounds in the Arctic. So do a number of ducks: Redheads, American Wigeons, Green-winged Teals, Northern Shovelers, Gadwalls, and Common Mergansers. Some Ross’s and Snow Geese stop here for the season, while others continue farther south. And then there are the unpredictable birds who generally winter north of our state, but may show up in some years, such as the Snowy Owl (below, left) and Common Redpoll (below, right).

Just as I tired of the unchanging weather while growing up in Southern California, we could become jaded always seeing the same bird species month after month. Migration ensures that I appreciate each and every species as they come and go. Don’t feel too abandoned, Mr. Memmott. They’ll be back.

The answer to last week’s quiz is Red-winged Blackbird (female).

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