April 23, 2009

For the Birds – Common Grackle

Chances are good that Common Grackles have returned to your neighborhood by now. These large members of the blackbird family are one of the first of our migratory breeding birds to come back to Maine.

With a sleek, glossy black plumage and a yellow eye, the adult Common Grackle is a striking bird. The birds are about 12 inches long, including the long tail. It is not easy to tell males from females although the head of males, in favorable light, has a glossy purple head and breast. The female is usually slightly smaller than the male. In flight, grackles hold their tails in a V, like the keel of a boat.

Despite their sleek appearance, grackles will win no contests for the beauty of their songs. Both males and females sing the same harsh, squeaky song that some ornithologists interpret as “squ-eek”, “readle-eak” or “scuda-leek”. Some people think the song sounds like the opening of a gate with a rusty hinge. These birds also give a characteristic raspy “chack” call, often in flight.

Males sing more frequently than females and male song rates are highest early in the breeding season. Any individual sings a single song but there is a lot of variation among individuals. The songs therefore seem to be useful for individual identification.

Grackles are habitat generalists. Suburban areas, farmlands, swamps, and orchards are all suitable. Favoring more open habitats, grackles are typically not found in deep forests. Before European settlement and the clearing of forests, Common Grackles were uncommon birds in New England; now they are abundant. Aided by the planting of shelterbelts, Common Grackles have expanded their range westward across the Great Plains.

This species is highly gregarious; if you see one, you will probably see 10. Except for females incubating eggs, grackles roost together at night in noisy roosts, sometimes more than 100 birds in one roost.

Unlike some of our long-distance migrants, Common Grackles do not winter very far to the south of us. Some winter in southern New England with more wintering from Pennsylvania south.

Once the grackles return, keep an eye out for their courtship displays. The male will raise the feathers around his neck, drop his wings and sing his song for a prospective mate. This behavior is called the song spread.

Pairs form soon after the birds arrive. The female builds the nest, usually well above the ground in a conifer. The male guards the female throughout the nest construction process. Once the nest is complete, the female will perform a wing quivering display, a signal that she is ready to mate.

The male aggressively keeps other males away from his mate. A common threat display is sky pointing, when the male raises his bill vertically. This behavior is given by one male on the approach of another male. The display usually results in one of the males departing.

Common Grackles may nest alone but more often in colonies of ten or more pairs in tall trees, especially evergreens. Sometimes, nests are made in freshwater marshes, old building and even the lower parts of Osprey nests. The nest is made of twigs and grass stems. Most nests contain 5-6 eggs, which the female incubates for about 14 days before hatching. The newly hatched birds are ready for their first flight in 14-16 days. Unlike their dark parents, juveniles are dark brown with brown eyes.

Grackles have a broad diet, although insects are the most commonly captured prey. Grackles often search for food on the ground, walking slowly and deliberately. Occasionally, a bird may run and leap into the air to catch an insect. Grackles may probe in the ground for earthworms and will even take them from robins. Grackles will also search for food in trees. Besides insects, grackles are known to eat spiders, snakes, lizards and mice. The eggs and nestlings of other birds are not safe from grackles. Grackles are even reported to wade belly deep in freshwater for crayfishes, minnows, frogs and salamanders. Grackles will eat seeds including corn, acorns, and seeds of various weeds. In fact, Common Grackles are now a major agricultural pest, causing millions of dollars of damage to sprouting corn.

Some Common Grackles attain impressive ages. The oldest known Common Grackle was banded in Michigan and recaptured 20 years and 11 months later in Illinois! A Common Grackle in Minnesota lived to be at least 17 years old while a New Jersey bird lived to be at least 16 years and 1 month old. The average life span is likely much less than these extremes.

[Originally published on April 4, 2009]

For the Birds – Geo-locating and Bird Migration

Keeping track of bird migration is a time-honored practice of naturalists dating back over 200 years. All of us delight at the arrival of the first Red-winged Blackbirds, Hermit Thrushes, or Yellow Warbler in the spring.

Until recently, our understanding of the timing of bird migration was based on populations of birds rather than individuals. We have to be able to follow individual birds to truly understand migration speeds and routes.

Bird banding has contributed some useful information. However, the chance of a bird bander capturing a bird banded earlier in the migration is pretty slim. The chance of capturing a banded bird immediately after its arrival is slimmer yet.

Outfitting birds with radio-tags that emit unique frequencies provides a way to track individual birds. The range of most radio-tags is limited to a couple of miles so this technology is more useful for tracking the movements of resident birds.

More recently, satellite transmitters have been developed that allow ornithologists to monitor the position of birds from their computers. For instance, researchers used satellite transmitters to track the migration of Short-tailed Albatrosses across the Pacific Ocean (http://www.wfu.edu/biology/albatross/shorttail/shorttail.htm).

Although radio and satellite transmitters have been miniaturized, they are still too large to place on most songbirds. A new technology, called geo-locating, promises to provide new insight into the pace and direction of small bird migration.

The geo-locaters were engineered by members of the British Antarctic Survey for use on larger birds and later miniaturized for use with songbirds. The songbird geo-locators are light (0.05 ounce). The device is essentially a small computer chip with a built-in clock and a short stalk. The geo-locator tracks light levels so that sunrise and sunset are recorded for each day. Knowing sunrise, sunset and day length allows the researchers to precisely determine the position of the bird every day. Essentially, the length of the day allows the latitude to be determined and the time of sunrise and sunset allows the longitude to be determined. Pretty neat!

The geo-locater is held on the rump of the bird with straps that wrap around the upper part of each leg.

The first results of this technique were recently published by a team of researchers led by Bridget Stutchbury from York University. The team captured 20 Purple Martins and 14 Wood Thrushes in the fall of 2007 in northern Pennsylvania. They were able to recapture five of the Wood Thrushes and two of the Purple Martins in the spring of 2008. The researchers downloaded the data from the geo-locater and were able to map the fall migration, winter movements and spring migration of each bird.

Even though only seven birds were recaptured, the results already cause us to rethink how migration occurs in songbirds. In the fall, the two Purple Martins flew south to the Yucatan Peninsula in five days (about 1500 miles in total). The martins stopped there for three to four weeks before continuing their migration to a wintering area to Brazil.

We know that spring migration is typically much faster than fall migration in most birds. There is an urgency about the spring migration as birds stream north to find mates and favorable territories. However, the speed of the Purple Martin spring migration was more rapid than suspected. One of the tagged martins flew from the Amazon basin back to Pennsylvania in only 13 days, traversing over 3000 miles. Four of those days were spent on stopover. Prior to this work, ornithologists believed that a nightly flight of about 100 miles was about the maximum distance most songbirds can manage.

Four of the five Wood Thrushes migrated to the southeastern United States, spending one to two weeks there before flying across the Gulf of Mexico to the Yucatan Peninsula. The birds wintered in Honduras and Nicaragua. Most of the thrushes returned to Pennsylvania in 13 to 15 days, again crossing the Gulf of Mexico. One thrush took the landward route, avoiding the Gulf crossing.

[Originally published on March 21, 2009]

For the Birds – Costa Rica Trip – Part II

This column is the second of two presenting some birding highlights of my visit to Costa Rica in January.

We left the rainforest reserve at La Selva bound for the Ecolodge at San Luis just west of the Continental Divide. The trade winds were unrelenting there, making birding by ear difficult and keeping the birds down.

One of the highlights was a pair of Emerald Toucanets, a mostly green small toucan. A pair of male Black-breasted Wood-Quail were fighting with other, oblivious to the ten people watching them.

In local pastures, I had nice views of Yellow-faced Grassquits, White-eared Ground-sparrows and a Social Flycatcher. Raucous Brown Jays were extremely common.

A local family maintained a bird feeder, stocked with fruit, that attracted Blue-gray Tanagers, Passerini’s Tanagers, Crimson-collared Tanagers (spectacular!), Buff-throated Saltators and Yellow-throated Euphonias. Old friends were seen in the trees: Black-and-White Warbler, Chestnut-sided Warbler and Baltimore Oriole.

We hired a taxi to take us from San Luis to the Monteverde Cloud Forest Reserve for a daylong adventure. This site was only 500 meters higher than San Luis but was truly a different world. Typical weather is misting rain with low-lying clouds. Epiphytes are everywhere on the trees.

The most sought-after bird at Monteverde is the Resplendent Quetzal, a specialist on avocados. We hired three guides to lead our class on a morning walk. The guides knew of an avocado tree where a pair of quetzals were feeding. With patience, we got a good look at a female through a spotting scope. Later in the morning, a male appeared briefly no more than 50 feet way.

The Resplendent Quetzal, a member of the trogon family, is often touted as the most beautiful bird in the world. I find it hard to argue. The male has a brilliant green head, throat and back and a scarlet red breast and belly. The tail is white with four long green uppertail coverts that extend well beyond the tail. The female is similar with more muted colors. Females lack the long tail coverts of the males.

This species is the national bird of Guatemala. Quetzals were revered by the Aztecs, Mayas and other Mesoamerican peoples.
Other avian highlights at Monteverde included a Black Guan, a roosting Mottled Owl, and Ochraceous Wood-Wrens. Several fearless Slate-throated Redstarts flitted about us for a while. These mostly yellow sprites are called candelitos (little candles) by Costa Ricans because their frenetic movements suggest flickering.

We saw seven hummingbird species including the large Green Hermit and Violet Sabrewing. Stripe-tailed Hummingbirds were seen as well. These hummers are nectar robbers. Many flowers with long tubular flowers rely on hummingbirds for pollination. The flowers essentially reward the hummingbirds with nectar for acting as pollinators. Striped-tailed Hummingbirds have relatively short bills. To reach the nectar of tubular flowers, the birds pierce the base of the flower to get the nectar but do not get a shower of pollen on them like other hummingbirds do.

Bananaquits and Common Bush Tanagers were nice finds as well.
Our last stop was the tropical dry forest of Santa Rosa National Park. This park is in the northwest corner of Costa Rica. We were there during the dry season when a strong rain shadow effect of the mountains to the east makes rain a rare event for half of the year. It was very hot during our stay.

Because of the dryness, some of the trees lose their leaves. The forest floor had a significant layer of dead leaves, similar to our northern broad-leaf forests.

The most conspicuous birds were White-breasted Magpie-Jays with their curly feathers on the top of the head. A Roadside Hawk, a buteo hawk, was regularly seen. Three species of parrots were heard and sometimes seen: White-fronted Parrot, Yellow-naped Parrot and Orange-fronted Parakeet.

For the Birds – Costa Rica Trip – Part I

My colleague Judy Stone and I spent most of January in Costa Rica teaching a Colby biology class. The focus of our course was plants of the tropics but I had time to enjoy some wonderful birding while we were there. I’ll devote this column and the next to some of the birding highlights of our visit.

Costa Rica is a small country, roughly the size of West Virginia. Within that small area, however, the range of climate, topography and vegetation is great. It is no wonder that 875 species of birds occur in Costa Rica. The United States and Canada combined scarcely exceed that number of species.

We spent our first week in Costa Rica at the La Selva Biological Station near the town of Puerto Viejo, north of San Jose. This site, at an elevation, of about 500 feet is lowland rainforest. The trade winds blow across Costa Rica from the east, bringing moisture-laden air off the Caribbean onto shore. As the air rises, it cools and drops the moisture as rain. We were at La Selva during the dry season but, as we learned, La Selva has a rainy season and a rainier season. We were lucky though as most of the rain fell during the evening hours.

The first bird I saw at La Selva looked like a small warbler, flitting near the top of a large tree. It was a warbler indeed but not the tropical species I was expecting. It was a Chestnut-sided Warbler, one of the most common nesting warblers in Maine. I noted a number of other birds that breed here in Maine enjoying the Costa Rican warmth: Turkey Vulture, Tennessee Warbler, Louisiana Waterthrush, Baltimore Oriole and Red-winged Blackbird.

We were assigned rooms in an older building called the River Station, overlooking the Puerto Viejo River. A pair of Crested Guans, chicken-like birds with bright red wattles, were feeding just above the trail on fruits. A Blue-black Grosbeak was in an adjacent tree.

Montezuma’s Oropendolas were the most conspicuous birds at La Selva. These members of the blackbird family are large and loud. Males are about 20 inches long, females five inches shorter. Most black, Montezuma’s Oropendolas have bright yellow tails and conspicuous white markings on the side of the head. Females were just beginning to build their pendant nests in palm trees. The nests are similar to those of a Baltimore Oriole but much longer. Males were displaying to females. The display is memorable. The male perches on a branch and gives a loud, liquid song. At a distance, the song is quite pleasing but metallic screeches can be heard when close to a male. As the male finishes his song, he performs a deep bow, rotating his body a full half turn, showing off his bright yellow tail. Despite the bravura performances, the females seemed unimpressed.

Mornings at La Selva were almost magical. Great Tinamous gave their wavering, flute-like call from deep in the jungle. Rufous Motmots gave their lovely hoot-hoot-hoot calls that reminded me of notes from a wooden percussion instrument. As dawn approached, the glorious songs of White-breasted Wood Wrens, Striped-breasted Wrens and Black-throated Wrens filled the air.

Parrots were vocal but usually difficult to see in the tops of trees. With patience, we got good looks at Mealy Parrots, Red-lored Parrots, Brown-hooded Parrots and White-crowned Parrots. The highlight though was eight fly-over Great Green Macaws. Only about 200 individuals are left in Costa Rica.

Birds at La Selva often move in large, fast-moving mixed flocks. One memorable flock had Palm Tanagers, Passerini’s Tanagers, Dusky-faced Tanagers, Blue-gray Tanagers and Golden-hooded Tanagers. Within five minutes, the flock had moved on.

I enjoyed seeing birds in families that were new to me. A Rufous-tailed Jacamar, related to the woodpeckers, looked alike an overgrown hummingbird with its long thin bill. A pair of Pied Puffbirds provided us with great views; these birds are also related to the woodpeckers. We saw Northern Barred Woodcreepers and Streak-headed Woodcreepers. Woodcreepers are perching birds that behave much like woodpeckers. A Great Antshrike gave me a brief look before diving back into its preferred dense undergrowth habitat.

Other memorable sightings included a male Green Honeycreeper with fluorescent green plumage, Olive-backed Euphonias, a Green Kingfisher and a ton of flycatcher species including Boat-billed Flycatcher, White-ringed Flycatcher, Common Tody-Flycatcher, Mistletoe Tyrannulet, Rufous Mourner, Bright-rumped Attila and Long-tailed Tyrant. Chestnut-colored Woodpeckers, Black-cheeked Woodpeckers and Pale-billed Woodpeckers were striking birds as well.

[Originally published on February 21, 2009]