The Wilson’s snipe (Gallinago delicata) is a small, chunky shorebird found across North America. It is known for making a distinctive, winnowing sound with its outer tail feathers during courtship displays and territorial flights. This weird zinging or bleating call is often heard before the bird is seen. But what exactly causes this strange sound and why do Wilson’s snipes make it?
Anatomy of the Wilson’s Snipe
Wilson’s snipes are medium-sized shorebirds measuring 25-28 cm (9.8-11 in) in length with a wingspan of 39-48 cm (15-19 in). They have short legs, a long straight bill, and cryptic brown, black, and white striped plumage that provides camouflage in marshy habitats.
The most distinctive feature of the Wilson’s snipe is its tail feathers. The outer tail feathers are unusually stiff, narrow, and twisted. The two outermost tail feathers lack barbs and are modified into thin, rigid shafts. When air rushes over these specialized outer tail feathers in flight, they vibrate rapidly and produce the winnowing sound.
Tail Feather Structure
The outer tail feathers of the Wilson’s snipe have the following structural adaptations that enable sound production:
- Narrow width to promote vibration
- Stiff vanes and shafts to produce resonant sound
- Asymmetrical with outer vane narrower than inner vane
- Barbules modified to maintain stiffness
The inner vane of each outer tail feather has small hooks that zip the barbs together, maintaining the feather’s rigid, asymmetric shape. This specialized structure transforms the tail feathers into vibration-producing reeds.
Mechanism of Sound Production
The Wilson’s snipe produces its winnowing sound through a process called vortex shedding. Here is how it works:
- Air rushes over the tail feathers as the snipe dives rapidly earthward.
- The airflow over the asymmetric tail feathers becomes turbulent, creating swirling vortices along the feather shafts.
- These vortices are shed off the trailing edge of each tail feather, creating pockets of low pressure.
- As the low pressure vortices detach and swirl away, the tail feathers are forced to snap back into position, causing them to vibrate.
- This rapid vibration generates the pulsing, bleating sound.
The alternating shedding of vortices causes the tail feathers to vibrate 180-250 times per second. This vibration produces pressure waves in the air that we hear as the characteristic winnowing sound.
Resonance Amplifies the Sound
The modified outer tail feathers act like tuning forks, resonating at a particular frequency determined by the size and stiffness of the feathers. This resonance amplifies the sound produced by vortex shedding.
Each tail feather vibrates at a slightly different frequency based on its length and stiffness. This produces a cascading ensemble of sound frequencies, creating the snipe’s pulsing, fluttering winnow.
Characteristics of the Sound
The winnowing sound of the Wilson’s snipe is a highly distinctive vocalization, often described as a bleating, humming, or buzzing noise. Here are some key characteristics:
- Made only in flight
- Pulsing, fluttering quality
- Variable pitch and volume
- Often precedes visual observation of the bird
- Involves outer 2-3 pairs of tail feathers
- Dominant frequency range of 2-5 kHz
- Sound can carry over 1 km in ideal conditions
The following table summarizes the acoustic properties of a typical Wilson’s snipe winnowing sound:
| Acoustic Property | Measurement |
|---|---|
| Dominant Frequency | 2-5 kHz |
| Duration | 1-2 seconds |
| Pulse Rate | 180-250 pulses/sec |
| Amplitude | 80-105 dB SPL at 1 m |
Listeners often describe the snipe’s winnowing as similar to the sounds made by an old hand-crank sowing machine, a bleating goat, or the winnowing fork used to toss grain into the wind to remove chaff.
Why Wilson’s Snipes Make the Sound
Male Wilson’s snipes perform winnowing display flights for the following reasons:
Defend Territories
The winnowing sound advertises the male’s territory and warns intruding snipes to stay away. Snipes defend territories both during breeding season and on wintering grounds.
Attract Females
Females are drawn to more robust and consistent winnowing sounds, which indicate a fitter male able to defend higher quality habitat. Choosy females select males based partially on their aerial displays.
Signal Alarm
The snipes may also vocalize to communicate alarm about potential predators. The fluttering winnow carries over long distances to alert other birds.
When and Where to Hear It
The best opportunities to hear the Wilson’s snipe’s winnowing sound are during the following times and locations:
Breeding Season
In spring and summer, listen for winnowing flights over meadows, marshes, bogs, and shorelines. The displays occur most actively at dawn and dusk as males compete for mates. Peak breeding season is May-July across Canada and the northern U.S.
Wintering Grounds
Snipes also perform aerial displays on wintering grounds from October-March. Listen for them in coastal marshes and flooded fields in the southeast U.S. and along the Pacific Coast. Dawn and dusk displays are most common.
Overhead Flight
Aim your eyes and ears upward when you hear the tell-tale winnowing. Snipes make the sound while performing steep, zig-zagging dives from heights of 200-300 m. The speed of descent enhances the fluttering effect.
Conservation Status
The Wilson’s snipe remains a widespread and relatively common shorebird species, but its populations face threats from habitat loss and degradation. Ongoing conservation efforts include:
- Wetland protection and restoration
- Sustainable forestry near wetlands
- Reduced pesticide use in agricultural areas
- Hunting limits
Ensuring suitable habitat across the snipe’s breeding and wintering range will be key to preserving populations of this sound-producing shorebird into the future.
Conclusion
The winnowing sound of the Wilson’s snipe is one of the most distinctive vocalizations in nature. This bleating, fluttering call is produced by specialized outer tail feathers that vibrate rapidly when air rushes over them during the snipe’s dramatic territorial flights. This unusual bird has evolved a mechanical instrument perfectly tuned to amplify its ethereal courtship call, one that has inspired writers and poets for centuries. Seek out wetlands at dawn and dusk to experience the snipe’s magical winnow for yourself.
