I am sometimes asked where I get ideas for weekly columns. Usually, the inspiration comes from a backyard bird or a morning walk, or when the neighbor’s dog finds a ruffed grouse nest, grabs an egg and carries it home miraculously unbroken, so that it can be rescued and taken to a wildlife rehab incubator. You know, simple stuff like that.
The incident happened last week, about the same time I was having my own adventure with a ground-nesting bird. I was leading a birding group in Baxter State Park, when suddenly a small bird flashed out of the weeds merely three feet away from me. I immediately knew that it had come off a nest. The dark-eyed junco had chosen a spot unbelievably close to traffic.
It’s a constant worry of mine. There are many ground-nesting birds in Maine, and I fret that if I lead a dozen pairs of feet tromping off a trail, someone will stomp a nest. I know, because I’ve come so close to doing it myself. I remember missing one white-throated sparrow nest by inches, seconds after warning my group to watch out for nests.
Hermit thrushes are the worst. I recall one thrush nesting in the middle of a Jeep trail, midway between the tire ruts. Several other nests were so close to the side of the trail that they might as well not have bothered trying to hide it.
If ground nesting is so perilous, why do many birds do it? Naturally, the short answer is because it works. If it didn’t, any bird following that strategy would have gone extinct eons ago.
It’s not like tree nesting is all that safe. Wind and weather take a toll. Tree nests are harder to conceal from predators. If a chick falls out of the nest, it’s a long way down. Whereas if a chick falls out of a ground nest, it’s a half-inch drop.
In many cases, there are practical reasons for ground nesting. Game birds generally produce a lot of large eggs and incubate for a long time. Upon hatching, the youngsters must be precocious enough to skedaddle right away.
The pilfered egg in the ruffed grouse nest was one of eight. It’s nearly impossible to build a tree nest large and stable enough to accommodate such a brood. Also, game birds are too clumsy to build a nest in treetops.
Large birds can build tree nests. Raptors, herons and egrets do it. However, they raise smaller broods.
Colonial seabirds are ground nesters on islands. What choice do they have? No trees. In fact, there aren’t many materials for building a nest. Common terns just scrape a little and lay their eggs on bare rock. Peregrine falcons do likewise, barely bothering to scrape before laying eggs on the ledge of a precipice.
One might think that web-footed birds can’t stand on tree branches well enough to build aerial nests. Most gull species nest on the ground. But the dainty Bonaparte’s gull nests in trees around remote lakes all over Canada.
Most shorebirds are ground nesters. In many cases, they are subarctic breeders nesting in treeless tundra. One exception is the solitary sandpiper, which is regularly seen on its spring and fall migrations through Maine. They are tree nesters, reusing old songbird nests.
Here in Maine, killdeer nest rather conspicuously on the ground in Bangor parks, golf courses and similar grassy areas. Spotted sandpipers are ground nesters along the edge of streams and offshore islands.
But why do some small songbirds nest on the ground, when they could just as easily choose trees? It’s likely that ground nests provide more camouflage, concealing their chicks deeper in vegetation. Nashville and Wilson’s warblers are ground nesters in Maine. Ovenbirds are champions, building a leaf-covered nest that looks like a Dutch oven. Grassland birds invariably nest deep inside unmowed fields. Maine’s vesper sparrows nest under lowbush blueberries.
Meanwhile, tree-nesting birds face the threat of raids from crows, jays and red squirrels. Hell hath no fury like a robin trying to drive off a hungry squirrel.
As for the grouse, the dog and the wayward egg, the story has a happy ending, mostly. The pilfered egg proved to be unbroken, but unviable. However, the ruffed grouse is fortunate that her nest was found by a frisky pooch, and not a raccoon, skunk, fox, opossum or snake. All these predators would have devoured the entire clutch without a second thought. Evolution and Mother Nature reward the birds that are best at hiding their ground nests.