The scream of the curlew is a haunting sound that echoes over marshes and mudflats worldwide. These large, long-billed shorebirds are famous for their loud, far-carrying calls that sound like long, bubbling screams. But what do these cries mean? Curlews use their screams for several important reasons that provide insight into their behavior and ecology.
Territory Defense
Curlews are highly territorial during the breeding season as pairs defend nesting and feeding grounds. The screaming call serves to deter intruders and announce that a territory is occupied. It is often given when a curlew spots potential predators like dogs, foxes, or humans approaching the nest. The piercing scream signals alarm and warns the intruder that they have been noticed. It also alerts the curlew’s mate to return and mob the intruder. Curlews will aggressively defend their turf against all kinds of trespassers with loud alarm calls and physical attacks from their long, pointed bills. Their haunting screams essentially proclaim “go away, this is our territory!”.
Communicating Over Long Distances
Another reason curlews scream is to communicate with each other over long distances. Their high-pitched calls carry several hundred meters across marshes and mudflats. Mates use the screams to locate each other and coordinate feeding and chick-rearing duties on vast tidal flats. The curving bill shape and large resonating gular pouch under the throat give their screams a far-reaching quality. Curlews on breeding and wintering grounds gather in large flocks of hundreds of birds. Keeping in contact with piercing screams allows them to coordinate their activities and movements as a group across huge areas. The screams serve to locate mates, signal intent, and maintain group cohesion.
Distress Calls
Curlew screams can also indicate alarm or distress. When a predator takes them by surprise or grabs a chick, curlews emit a panicked series of screams. This harsh crying alerts the group that danger is present and defense is needed. The intensity and urgency of the screams signify how threatened the curlew feels. Curlews may also scream in pain if injured by a predator. Their screams draw attention and mobilize other curlews to harass the predator. Loud alarm calling and mobbing are their main defenses against predators. The curlew’s disturbing screams essentially cry “danger, come help!”.
Nocturnal Flight Calls
Curlews also vocalize in flight, especially on moonlit nights during migration. Their evocative screams serve to maintain contact in the darkness. The calls help them coordinate their migratory flocks over long distances when they cannot see each other well. Curlews often migrate in large numbers at night when risks from some predators are reduced. Screaming back and forth allows them to stick together and track the flock’s progress. The echoing cries punctuate the night sky as the birds stream overhead on their long migrations.
Behaviors Associated with Curlew Screams
Curlews engage in various behaviors associated with screaming vocalizations based on the context and reasons for calling:
Aggressive Postures
When used to deter territorial intruders, curlew screams accompany aggressive body postures. Curlews stand tall with feathers puffed up to appear larger, spread and flap their wings, and jerk their heads back and forth. This heightened response intends to intimidate intruders. Their dramatic screams and postures signal escalating aggression if the intruder fails to leave the territory. Intruders risk injury from stabbing blows of the curlew’s long, pointed bill.
Circling Flight
Both mates may take to the air and circle overhead while screaming to drive an intruder away. Their piercing alarm calls indicate to the predator that it has been spotted and will be vigorously mobbed if it persists. The agitated, circular flight patterns and loud screams present a united front that most predators heed as a signal to retreat. This circling flight behavior allows curlews to remain safely out of reach while aggressively proclaiming ownership of their territory.
Bobbing Motions
Curlews often bob their heads rhythmically up and down when uttering screams. They tend to do this during the long, crescendo portion of each call. Experts think this motion may help project and resonate the screams. Bobbing may also enhance their visual display to any intruders or predators receiving the alarm calls. The combination of loud, piercing screams with head bobbing presents a dramatic warning to heed their cries and back off.
Hunched Postures
In response to alarm calls from their mate or others in the flock, curlews often adopt a hunched, frozen posture after screaming. They crouch low with neck extended horizontally and scan for the source of danger. This posture makes them less visible and allows quick reaction if the predator attacks. Their outstretched neck position also enhances directional hearing to pinpoint the predator’s approach. Freezing after alarm calling enables curlews to both warn others of danger and prepare for appropriate response.
Mobbing
Curlews aggressively mob most predators after sounding alarm screams. They gather and swoop in concerted attacks from all directions, screaming constantly. This mobbing behavior is designed to distract and intimidate the predator until it departs the area. Curlews strike at the intruder with their bills and feet while evading counterattacks. Their nonstop screaming and diving bombardments often convince predators to cut their losses and leave. Mobbing provides an effective defense for curlews, especially during nesting when chicks are vulnerable. The screams call others to join the counterattack.
Adaptations for Screaming
Curlews possess specialized physical adaptations that allow them to produce their loud, far-carrying screams:
Large Body Size
Curlews are among the largest shorebirds worldwide, ranging 22-28 inches in length and up to 2 pounds weight for the largest species. Their large body size produces greater lung capacity to generate the air volume needed for loud screams. It also provides greater physical stamina for prolonged calling sessions.
Long Bills
Their extremely long, curved bills up to 8 inches give curlews a natural megaphone for amplifying calls. The bill shape focuses and projects their piercing voices over much greater distances. Curlews are able to scream at volumes in excess of 90 decibels – as loud as a lawnmower!
Gular Pouch
Curlews have an expandable gular pouch of loose skin between their lower bill and throat. They fill this pouch with air on inhalation when screaming. The ballooning pouch acts like a resonator to augment and carry the sound. The gular pouch gives their screams a wavering, tremulous quality.
Large Eyes
Curlews have very large, prominent eyes that may also help amplify their screams. The eyes’ position surrounds the head’s axis of rotation. Rapid spinning of the head when screaming may enhance sound projection, like a radar dish. The bulging eyes protrude from the turning head on each rotation to blast the call in all directions.
Wing Spreads
Curlews often spread or flap their wings when emitting screams. This makes the birds appear larger and more threatening. It also exposes the white underside of the wings, creating a flashing signal visible over greater distances. Spread wings may also help channel and direct their screams in specific directions during territorial displays.
Reasons for Seasonal Differences
The frequency, context, and meaning of curlew screams vary during the year due to seasonal factors:
Breeding Season Defense
Screaming escalates during breeding season as curlews fiercely defend nesting territories. Calls proclaim ownership of breeding sites and aim to deter intruders. Screams are issued upon sighting any potential threats near the nest. Constant vigilance is required when vulnerable chicks are present.
Coordination of Large Flocks
Outside of breeding season, curlews gather in enormous flocks. Frequent screaming maintains contact between flock members as they roam to feed over vast mudflats or migrate thousands of miles. Screams coordinate the flock’s synchronized movements.
Establishing Wintering Territories
Upon reaching wintering grounds, screaming resumes to establish and mark seasonal territories surrounding prime feeding areas. Winter sites may change yearly, so curlews must re-secure territories with loud alarm calls each migration.
Seasonal Aggression Changes
Breeding curlews fiercely attack any intruders with maximal aggression. But wintering birds are less territorial and may tolerate other species utilizing the same feeding areas. Screams are used more for signaling flock movements rather than driving off intruders during the non-breeding period.
Predation Risks Vary
Some predators are seasonal migrants themselves, so risks differ throughout the year. The relative threat of different predators may dictate when curlews need to scream the loudest to summon help with defense. Predation of chicks mandates intense screaming as a first line of defense during breeding season.
Habitat Availability Shifts
Curlews shift habitats between breeding and wintering grounds based on seasonal availability. The nature and extent of flat feeding areas determines whether prolonged, far-reaching communication is needed between flock members. Curlews scream the most across vast tidal flats providing safety in numbers.
Curlew Scream Meanings
In summary, curlew screams can communicate the following meanings:
| Scream Context | Intended Message |
|---|---|
| Territorial defense | “Go away, this area is occupied!” |
| Intruder alert | “Threat approaching, defend territory!” |
| Communicating over distances | “Where are you? I’m over here!” |
| Predator surprise attack | “Danger, help me!” |
| Injury from predator | “I’m hurt, come assist!” |
| Nocturnal flight | “Stay together, this way!” |
| Alarm for predator | “Gather to mob the intruder!” |
Conclusion
The haunting screams of curlews serve many important purposes for the birds throughout the year. They defend territories, communicate over distances, signal threats, and coordinate movements in various contexts. The meaning behind the screams provides insight into curlew behavior, ecology, and adaptations. Understanding why curlews scream reveals their strategies for survival on mudflats and marshes worldwide. When you next hear the cry of a curlew, listen closely – its screams are full of information about the challenges faced by these evocative shorebirds.
