For a couple of hours on May 19, 2017, I drove the blacktop Tour Route through fields at Middle Creek Wildlife Management Area in southeastern Pennsylvania, as I have most years in the recent past, to see what small, nesting birds were visible to most anyone in vehicles along that route from the middle of May to the end of June. Those attractive birds are most visible when perched on roadside bird boxes, plants, wires and signs. They are in order of abundance at Middle Creek, tree swallows, red-winged blackbirds, eastern bluebirds and eastern kingbirds.
Tree swallows, as a species, raise young in cavities in open areas with some trees, usually near water. The fields and a lake at Middle Creek attract these swallows to that area and the many bluebird boxes erected along the rural roadsides, boxes they took over, offer nesting places for them. I have often seen a few pairs of tree swallows joining forces to unrelentingly harass a lone pair of eastern bluebirds, forcing the latter species to abandon bird boxes.
Tree swallows seemed formally attired and are entertaining to watch in mid-air. Adult males are metallic blue on top and white below, while females and young are bluish-gray above and white underneath. And groups of them are interesting to see perched on bluebird boxes and roadside wires, and sweeping low over fields and water after flying insects they catch in their beaks and feed to their young in cavities.
Red-winged blackbirds have long been adapted to nesting in cattail marshes and fields of tall grass. The striking males are black with red shoulder patches and females are chocolate-brown with darker streaking. Each male sways on top of cattails and tall grasses to sing his "konk-ga-reeee" songs to establish territory and attract a mate for nesting. Each female makes a cradle of grass that she attaches to a clump of grasses. Red-wings consume a variety of invertebrates they pick off plants in their territories.
Though some pairs of beautiful bluebirds are hassled and driven away by gangs of tree swallows after nesting boxes, other pairs of these blue and rusty thrush relatives hatch youngsters in bluebird houses in the fields at Middle Creek, as elsewhere. Bluebirds perch on roadside poles, wires and signs and drop to the ground to grab and eat invertebrates. Each bluebird pair rears up to three broods of babies in hollows during spring and summer.
I was surprised by the numbers of eastern kingbirds I saw that day at Middle Creek, though this species has been increasing in numbers locally in recent years. Kingbirds are members of the flycatcher family, a family of small birds that catch flying insects in mid-air. Gray above and white below, with white on the end of their dark tails, eastern kingbirds seem to be in formal dress, as are tree swallows. And while many of their flycatcher relatives nest in woodlands, kingbirds prefer open country with a few, scattered trees.
Kingbirds perch on twigs, wires and fences and watch for passing insects. When prey is spotted close by, kingbirds flutter out on shallow wing beats, which is interesting to see, grab their victims in their beaks and zip back to their perches to eat their prey and watch for more. Kingbirds place their twig and grass cradles on the twigs of trees in fields and feed their young some of the flying insects they catch on the wing.
I was happy to see a few each of yellow warblers and common yellowthroat warblers in dense patches of shrubbery in the fields, especially those of blooming blackberry canes. The lovely males of both kinds sang their territorial songs from the tops of that vegetation, giving me hope they will nest there, a place they had not raised young in recent years when the blackberries and other shrubs were not yet there. Plant succession causes wildlife to shift living and nesting areas to find habitats they are adapted to. For example, while these warblers, hopefully, found new nesting spots in what had been grass fields, grassland birds had to move to another nesting location of tall grasses.
Which brings me to bobolinks, which are small, grassland blackbirds. I saw two dapper male bobolinks singing while in flight and when perched on tall grasses, but not the score or more of male bobolinks establishing nesting territories in that same large field a few years ago. With the influx of blackberry canes and other shrubbery in that field, brought in by seeds in bird droppings, bobolinks have been discouraged of nesting in it. Kingbirds, yellow warblers and common yellowthroats favor that field the way it is now, but not the bobolinks. As plant communities change in composition, many species of wildlife often move about to find the habitat they are adapted to. Grasslands being dispossessed by deciduous thickets and woods are a major example of plant succession. So only a few bobolinks remain in that field that once held several pairs of them and their young of the year. Tree swallow, red-wing and bluebird populations have held steady at Middle Creek because nothing major has changed in their niches, but kingbird populations have risen in farmland, partly because of that species' adapting to farmland conditions. Yellow and common yellowthroat warblers are moving into new shrubby habitats, but bobolinks are losing nesting grounds because they haven't adapted to changing field conditions to their benefit. Those small, striking blackbirds can only flourish in large fields of tall grasses.
No comments:
Post a Comment