Summer began right on schedule a few weeks ago, but no sooner did it arrive than it started to fade. The first day of summer has the longest stretch of daylight of the year. Already days are getting shorter. It's difficult to notice at first, but by late July, shorter days will be obvious.
Photoperiod, the amount of sunlight in a day, is nature's most accurate timepiece, and virtually all plants and animals use it. Migratory birds return in April and May. Butterfly milkweed flowers in June, and my trumpetcreeper just started to bloom. In nature, timing is everything.
Impressive example: If you head to the east coast this month, you'll notice an even more impressive example of natural timing. Believe it or not, the southbound shorebird migration is underway.
By the end of the first week of July, flocks of shorebirds can be seen flying south along New Jersey beaches. And they aren't local birds. They're southbound sandpipers that nested in northern Canada. Yes, it's July, and migration is underway. Arctic summers are brief, and shorebirds waste little time after arriving on the nesting grounds in May.
Many shorebirds migrate long distances. They nest in the arctic and winter in the southern hemisphere. When they move north in the spring, they usually pass through New Jersey in early May. Their timing is critical. In May, horseshoe crabs move from deeper water to the beaches of the Delaware Bay. Here they lay thousands of eggs in the sand in an ancient ritual that insures the survival of the species. .
Shorebirds, by the tens and hundreds of thousands, time their passage to take advantage of the super-abundant food. For a week or more, they swarm the bay's beaches and gorge on the freshly laid caviar. .
Predictable get-together: This predictable get-together of shorebirds is one of the planet's most spectacular natural events. One year my travels took me to south Jersey in mid-May, so I spent a morning at a small community called Reed's Beach. Rarely have I ever seen so many birds in one place at one time. .
From a distance, the beach itself seemed to writhe with life. Through binoculars, the source of the movement became obvious. Shorebirds, mostly ruddy turnstones and red knots, foraged for crab eggs. The numbers were beyond counting. If someone had told me there were a million shorebirds on the bay that day, I could not have argued. It ranks as one of my most memorable birding experiences.
When they are fat and ready to breed, the shorebirds continue the journey north. They arrive on the nesting grounds just as the last snow and ice thaws. .
Most shorebirds lay clutches of three or four eggs in a scrape of a nest similar to the killdeer, a locally common shorebird that often nests in lawns and gravel driveways. And they rely on cryptically marked plumage to protect them from Arctic predators. Incubation lasts three to four weeks. This lengthy incubation period insures that embryos have enough time to develop into down-covered precocial chicks, which can leave the nest within hours of hatching. Under attentive parental care, young shorebirds grow rapidly. Some species can fly in as little as three weeks.
Essential adaptation: Rapid growth and development is an essential adaptation to arctic life. Winter can strike early; August snowstorms are not unusual. Fortunately, the environment also provides the means for rapid growth and early migration.
Summer days in the arctic are long. The sun shines for 20 hours or more. That means a young arctic killdeer, for example, can forage for at least six hours more each day than their mid-Atlantic counterparts. As a result, arctic birds grow faster and fledge sooner. That's why arctic shorebirds can head south in July.
Because the environment compels arctic shorebirds to complete their nesting cycle quickly, they are among the best examples to make the point that migratory birds are not northern birds that go south for the winter. Instead, they spend most of the year in Latin America and come north only to nest. Even hummingbirds, warblers, and tanagers spend only about four months of the year in temperate North America.
And they do it all without watches or calendars.