Bristle-thighed Curlew

The Bristle-thighed Curlew is a medium-sized bird that have been marked near threatened by the IUCN. Although Bristle-thighed Curlews were discovered as early as 1869, their breeding habitat was not discovered till after the end of the 19th century. This bird species was first located in Alaska, and for the longest time ornithologists believed that this species was perhaps a vagrant. Perhaps this was because this species is not particularly easy to locate.

About Bristle-thighed Curlews

Only by the end of the 19th century, some ornithologists came to the conclusion that Alaska is possibly a breeding ground for this species. Almost half a century later, the nesting sites of these birds were located. As the first nest of this species was discovered in 1948, it was one of the last North American birds to have their nest and egg description document. The first nest was found north of the lower Yukon River.

This species only nests in the tundra, specifically in two areas in Alaska. Its wintering grounds are found in Oceania. In the late 1980s, some ornithologists finally decided to study these birds in detail. For a certain period, they were being studied year-round. From surveying this species, it was found that their numbers are not larger than 10,000 in total. Both breeding areas were home to approximately 3,500 breeding pairs.

Bristle-thighed curlews are unique birds that indulge in behaviors that are particularly characteristic of most other shorebirds. No other shorebird winters exclusively on oceanic islands. Another interesting and unique characteristic of this species is their usage of tools during foraging. These birds also consume extra food to build up their fat stores so that they can perform nonstop flights while migrating. Another interesting feature is their ability to shrink their nutritional organs while migrating. With the help of these adaptations, they can engage in non-stop flights for over 2,500 miles. During most of these nonstop migratory flights, these birds cover more than 3,000 miles.

Not only do these figures seem impressive, but they are also excellent. There are only one other bird species (Bar-tailed Godwit) that is capable of achieving such a feat. These large birds command large territories that can range up to 275 hectares. They do so by performing magnificent aerial displays and making complex vocalizations.

After Bristle-thighed Curlew chicks hatch, the parents care for them for a few weeks before leaving for the Alaskan Coast. These nestlings are cared for by some adult Bristle-thighed Curlews residing in that area. Parents use this time to consume an excessive quantity of fruits to fatten up. This food will assist them in migrating southward. Younglings take more time to reach the staging grounds.

Bristle-thighed Curlews are consistently reducing in numbers, but the exact reason for this has not yet been identified. Ornithologists are speculating that exotic mammalian predators could be the reason for the high mortality of this species. Otherwise, the habitat of these birds is mostly undisturbed. Like many other bird species are suffering from human interference, this species has still not experienced the effects of significant human-related disturbances.

● Bristle-thighed Curlews Photos, Color Pattern, Song
● Bristle-thighed Curlews Size, Eating behavior, Habitat
● Bristle-thighed Curlews Range and Migration, Nesting

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Bristle-thighed Curlew Color Pattern

The plumage color of Bristle-thighed Curlews is variable. Underparts are mostly buffy or cream, and sometimes rich cinnamon. In contrast, their upper parts are dark-brown to gray-brown. Bold markings are present on their head.

The color of their auriculars, neck, and cheeks is buff, with the presence of a few brown streaks. The only portions of their body that are white and mostly unmarked are the upper throat and chin.

Juveniles have similar plumage, but they are more brightly patterned. On the wintering grounds, a knowledgeable birdwatcher can differentiate between adults and juveniles by observing the brightness of their plumage feathers.

Description and Identification

Bristle-thighed Curlews are often confused for Whimbrels due to their physical similarities. Both these species also occur along with the same range. The easiest way to distinguish Bristle-thighed Curlews from Whimbrels is by paying attention to their vocalizations. In contrast to the loud sequence of “bibibibibibibi” notes uttered by Whimbrels, Bristle-thighed Curlews utter a whistled “chiueet”. If one if focusing on physical differences between these two species, they are easier to identify when these birds are in flight.

Bristle-thighed Curlews are known for their characteristic and melodious vocalizations. Not many other sounds heard in the tundra of western Alaska are as evocative. Although vocalizations similar to those made by other curlew species are present, Bristle-thighed Curlews expertly manage to elaborate simple pure tones. These birds are experts at singing to produce a dramatic effect. Their vocal talents have made these birds very intriguing to the scientific community.

Some of the vocal repertoires of this species are also found in Whimbrels, but with minute differences. Hatchlings utter peep calls to contact their parents, and a much harsher “whee” call when they are in imminent danger. In a very short span of time, the vocal repertoire of younglings develops. Once hatchlings are 3 weeks old, become capable enough to make several vocalizations, and soon by the time they are 5 weeks old, they can start to attempt their characteristic complex whistle.

Bristle-thighed Curlew Song

The song produced by Bristle-thighed Curlews is a melodious combination of their other vocalizations. Their song sounds somewhat similar to the attention whistle made by humans. The nature of the song also differs according to the sex of the Bristle-thighed Curlew.

As we know, this song is complex, and hence contains several variations in the song elements. The song is the loudest at the beginning and the end of the song with many dramatic variations in between. The variations in amplitude and frequency are directly proportional to each other.

This call includes a sequence of “chiu-eets” with variations in their rate, frequency, and loudness. These variations differ according to the context of the song. Males are known to sing at higher frequencies.

Another call made by Bristle-thighed Curlews is their low whistle. This call shares a few similarities with the call produced by Whimbrels. The low whistle has been described as the sound made by the reverse parking sensor when a reversing car/truck approaches an obstacle. Both Whimbrels and Bristle-thighed Curlews can sing identical renditions of low whistles, so it is not the best vocal cue to differentiate between them. In that case, the complex whistle is significantly more reliable.

Complex whistles are characterized by their regular frequency spikes which can range from 1-3. Constant frequency modulation is observed between these spikes. Their whine is another call that is made by Whimbrels. The only difference in the calls of both these species is that Bristle-thighed Curlews have slight modulation of amplitude and
frequency. Therefore, it can be assumed that Bristle-thighed Curlews are overall better singers than Whimbrels. This information might not be crucial in identifying this species, but it might enrich the experience of the birdwatcher who is able to find both these species and observe the gentle differences.

As discussed earlier, their song is nothing but a combination of most of these calls. It begins with a sequence of low whistles, followed by complex whistles, and mostly sends with a series of low whistles, or whines. Whines are not as common at the end as low whistles, and sometimes the ending can be a combination of low whistles and whines. This
song contains a number of complex modulations in between each call that is a part of it. There is a need to study the meaning of these complex frequency modulations.

Shrill whistles are another notable call made by these birds. This call is almost gull-like. It’s a piercing scream that is almost constant in amplitude throughout its length except in the beginning and at the end. The beginning has a rapid rise in frequency, and the ending has a rapid fall before the call ends. They also produce a few other calls, but not as frequently.

Bristle-thighed Curlew Size

Bristle-thighed Curlews are medium-sized shorebirds. They are 15-17.4 inches long, with a wingspan that is almost double the length of their body. Females are slightly larger than males.

Bristle-thighed Curlew Behavior

Bristle-thighed Curlews are strong ground foragers. These birds are quite relaxed while feeding on vegetation such as berries. They like to walk around while foraging for suitable berries. These otherwise relaxed birds are extremely quick while chasing prey such as lizards or spiders.

Although they prefer being on the ground through most of the year, they are often perched on trees in the winter. Most wintering grounds inhabited by them contain trees, in the absence of which adult Bristle-thighed Curlews find any objects with suitable elevation to guard their younglings against intruders or predators. They use this perch to make their alarm calls. As these birds are quite large, they need to spread their tail and open their wings to balance objects or areas with high elevations.

Bristle-thighed Curlews are remarkable fliers. They can manage to outfly even the best of flying predators such as falcons. Flying is not often observed, except during migration, and during courtship displays.

Several aggressive encounters have been observed in this species. These encounters can be between a couple of Bristle-thighed Curlews, or against common intruders of predators. These encounters can occur on the ground or in midair. Bristle-thighed Curlews rapidly follow their opponents and attack their posterior ventral regions with their bills. Although not all physical encounters include physical contact, most do.

Bristle-thighed Curlew Diet

Bristle-thighed Curlews mainly feed on spiders, insects, flowers, and fruits on their breeding grounds. They don’t seem to be very specific about the food they consume. During winters, their food intake becomes more animal-based. They seem to be opportunistic during this time, ingesting anything that is available. Common foods consumed during winters include seabird eggs, invertebrates, carrion, rodents, lizards, fruits, and hatchlings.

Bristle-thighed Curlew Habitat

In their breeding range, Bristle-thighed Curlews mostly prefer rolling hills which are covered with upland tundra. These hills generally have slight elevations and minor slopes. Their wintering habitats are located exclusively on oceanic islands.

Range and Migration

Bristle-thighed Curlews travel large distances during migration. They are known for their impressively long non-stop flights. These birds breed in only 2 areas, one of them is in Western Alaska, and the other one is on the north-central Seaward Peninsula.

Bristle-thighed Curlew Lifecycle

Bristle-thighed Curlews mostly arrive individually, or in groups of two to the breeding grounds. On rare occasions, flocks of Bristle-thighed curlews might travel together to their breeding grounds. Mostly, birds that have already established pair bonds arrive together. If pair bonds are not formed, males arrive earlier than females.

Bristle-thighed Curlews raise only one brood per season. Only half of their nesting attempts are successful. In most cases, eggs need to be incubated for 8-10 days.

Nesting

Bristle-thighed Curlews place their nests on the ground. These nests are mostly very well hidden amongst lower vegetation. These nests are usually very difficult to find. Dwarf-shrub meadows are preferred spots for nesting. It seems like the nests which are constructed under dwarf willows have a higher success rate.

Nest sites are typically chosen by males for their presenting scraping displays. Nest material is added by both males and females after a pair is formed.

Anatomy of a Bristle-thighed Curlew

Bristle-thighed Curlews are large birds with long bills that are curved downwards. Their wings are twice the size of their body.

Final Thoughts

The non-stop flying ability of Bristle-thighed Curlews is truly awe-inducing. It is remarkable that any bird can achieve such a massive feat. Not only are these birds experts at flying during migration, but they are also such splendid singers. An enthusiastic birdwatcher would definitely enjoy sighting these birds when are singing or flying.

Ornithology

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