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One of the earlier arriving neotropical migrants every spring, even palm warblers were piling up locally in big numbers waiting for warmer weather and the emergence of insects. Keith Corliss

Flight Lines: Migrant birds savor warmth, too

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Early last week the dam finally, thankfully, broke. The endless cold of a protracted spring gave way to warming on a level we have all been eagerly anticipating for well, months actually.

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Cyclists, joggers, dog-walkers; everyone got out. Lawn mowers were humming, cars were being washed, lawn cleanup was happening in earnest. All those chores put off until the “weather gets nice” were suddenly being tackled. It is astounding what warm spring weather will stimulate in activity among the local populace. Equally amazing is the fact that virtually all organisms are reacting in similar fashion.

For a couple of weeks leading up to about last Tuesday, things were looking and feeling quite slow in terms of spring progress. Sure, we’d had a smattering of decent days but not enough to make things really pop. Trees which typically flower early were reluctantly slow to do so. Other late trees were barely showing signs of swollen buds.

It wasn’t just us either. To the east, similar weather had been occurring. On a recent trip to the Upper Peninsula of Michigan, a local resident relayed an illustrative story to me. His wife, he said, keeps a daily account of natural happenings around their place. In other words, she tracks the phenology of the local area (phenology is the science of the timing of natural events such as bird migration). According to him, his wife claimed that spring peepers (a very early and loud northern frog species) had been late emerging this year by six weeks.

For all of nature this is nothing new, of course. Each organism is well equipped to withstand a little give and take with climate, especially here in the northern hemisphere. Still, songbird migration is a bit of a gamble despite the fact it’s largely based on thousands of years of genetic imprinting and precedence. To arrive as early as possible on nesting grounds affords the obvious advantage of getting to choose the optimum nesting location. Get there too late and all the good spots might be taken. Arrive too early and the obvious risk is starvation due to cold weather.

In broad generic terms, those species which feed on plant growth and seeds will show up earlier, able to glean whatever tidbits become exposed by melting snow. Those birds that rely upon invertebrates (spiders, insects, worms) arrive somewhat later. It’s these insectivores that showed signs of struggling leading up to last week. The argument that the migration timing of the bug eaters comes with more risk is an easy one to make.

For many days several warbler species (a family of largely insectivorous neotropical migrants) could be seen on the ground grubbing for whatever the birds could find among the scant greenery. Keep in mind these are birds more at home high up in the tree canopy. They even peppered asphalt roads and parking lots in search of some morsel that might hold a calorie or two to sustain them.

A piece of open water near town was crazy with swallows about 10 days ago. There were easily 2,000 birds representing all the expected swallow species for this area; all were making continual passes low over the water. This was another case of very hungry bug-eating birds hanging on in anticipation of warmer temperatures which, in turn, would stimulate insect emergence.

Last Tuesday, though, was different. It was sunny, it was nearly windless, and it was warm. Species which were absent the day before had arrived in the dark (the vast majority of songbirds are night migrants). Flocks of songbirds were everywhere in the trees – warblers here, vireos there, thrushes behind every snag. A chorus of singing was heard –northern parula, Chestnut-sided warbler, Connecticut warbler; a palpable energy pulsed in the air. For nearly the first time this calendar year, there was likely enough food for everything to be fed to full.

These migrants won’t stay of course. To the birds, we represent merely a pit stop--albeit a critical one – on the way to summer nesting grounds. Without the fat reserves gotten here with the consumption of caterpillars and other emerging morsels, the odds of a successful journey and subsequent nesting attempt greatly diminish. While we may relish the chance to comfortably wear shorts once again, it’s interesting to note that there are other organisms not only welcoming the warming but that their very existence depends upon it.

Corliss is a West Fargo resident, avid birder, and ND Game and Fish volunteer instructor. He serves as a corporate pilot for Forum Communications. kcorliss@forumcomm.com.

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