Storm birds, also known as storm petrels, are a family of seabirds found across all of the world’s oceans. There are around 20 species of storm petrel, all of which are relatively small in size with long wings, short legs, and webbed feet. Storm birds are well known for their association with storms, often seen skimming over the waves or resting on the sea surface even in rough conditions. But what sort of noises do these birds make? Their calls and vocalizations provide some insight into the behaviors and adaptations of storm petrels.
Normal Calls of Storm Birds
Storm petrels may be named after storms, but when conditions are calm they have some soft and pleasant calls. These are used for communicating with other individuals of their own species, likely for keeping together in flocks and pairs during foraging and migration. Some examples include:
– Purring calls – Some storm petrel species have a cat-like purring call used in mating displays and communicating with their mate. The purring is created through rapid vibration of the syrinx, the bird’s sound-producing organ.
– Chattering calls – Species like the European storm petrel have a fast chattering call that sounds like a quick repeated clicking or rattling. It serves for close-range communication between pairs or colony members.
– Whistling – Soft whistling notes are created by some storm petrels, like Wilson’s storm petrel, using their syrinx and upper vocal tract. The whistles have a high pitch and help the birds stay in acoustic contact.
– Chirruping – A number of storm petrels, like the Swinhoe’s storm petrel, communicate with short chirrups or twitters. It’s another social call for coordinating activities within a colony.
– Cooing – Some species have cooing or moaning calls, like the bearded reedling’s ‘kroo-kroo’ vocalization. Though not technically a storm petrel, the bearded reedling occupies a similar oceanic niche.
Calls in Windy Conditions
Storm birds tend to become more vocal when winds pick up and stormy conditions arise. Their storm-related calls include:
– Piercing cries – High-pitched shrieking or piercing cries are made by many storm petrel species in windy conditions or when overfeeding schools of fish. The powerful cries can carry far and likely help scattered birds relocate the feeding flock.
– Wailing calls – Some storm petrels emit a wailing ‘kee-ah’ call when winds get high. The European storm petrel is known for its wailing cry that may help communicate over wind and waves. It also could signal alarm or excitation.
– Rapid chatter – Species like Leach’s storm petrel produce a fast ticking or chattering call when winds pick up or during rainstorms. Made in flight, it may coordinate flock movements in the noisy conditions.
– Screaming – High, screaming calls are made by some species, like the black-bellied storm petrel, when feeding or flying in stormy habitats. The harsh screams can carry over considerable distances in wind.
– Snapping bills – Along with vocal calls some storm petrels, like Wilson’s storm petrel, snap their bills together loudly producing a snapping or popping sound in flight. The purpose may be communication and individual identification in loud conditions.
– Humming – A few species vibrate their wings in flight to produce a humming or buzzing sound. Made only on the breeding colonies, this may communicate excitement or signal location in windy environments.
Noises Made on Breeding Colonies
Storm petrels nest in dense colonies on remote islands, rocky coasts, or in forested habitats. Here they produce a range of distinctive noises:
– Screeching – High-pitched screeching calls are made on breeding colonies, likely for territorial signaling between pairs. The screeches may also stimulate courtship feeding by mates.
– Chattering – Rapid chattering or clicking is used on the colony among pairs or young. This serves to maintain acoustic contact at close-range in often noisy colony environments.
– Purring – The cat-like purring call is made by some species as part of courtship rituals on the breeding sites. Purring helps maintain the pair bond and may stimulate mating behaviors.
– Bill-snapping – In the dense colonies storm petrels snap their bills loudly, which may mark territory or signal mate recognition amid the noise.
– Wing-humming – Some species create buzzing wing hums on the colony during courtship rituals or territorial interactions. The unique hum likely facilitates individual identification.
– Begging calls – Chicks beg for food from parents with loud rasping or squealing calls. These help guide parents to nest sites and stimulate feeding in the dim, crowded colonies.
Other Storm Petrel Vocalizations
Some additional storm petrel noises and calls include:
– Nocturnal flight calls – Storm petrels are highly active at night. Some give soft chirping or whistling flight calls to maintain contact in darkness.
– Distress calls – Harsh alarm calls are made when predators like gulls, skuas, and owls attack. These alert others and try to draw attention.
– Take-off calls – Brief take-off calls accompany flight as storm petrels become airborne after landings.
– Aerial display calls – Various squeaks or whistles are made in flight displays over colonies, likely advertising the nest site.
– Landing calls – As they prepare to land storm petrels often give a contact call that may coordinate landing in crowded areas.
– paired signaling – Members of a pair perform vocal duets or coordinated calls to identify each other on noisy colonies.
Mechanisms for Call Production
Storm petrels have anatomical adaptations that allow them to produce their unique calls:
– Syrinx – The syrinx is the avian sound-producing organ, located at the branch point of the trachea. Muscular control of the syrinx membrane allows production of diverse noises.
– Elongated trachea – Storm petrels have an elongated windpipe or trachea. This allows them to make and modulate more complex vocalizations.
– Throat air sac – An inflatable sac near the syrinx acts as a resonator, amplifying and modifying vocalizations. Storm petrels can control the throat sac to increase call volume.
– Bill shape – The short, hooked bills of storm petrels may increase call directionality, allowing communication in windy environments.
– Rictal gland – An oil secreting gland by the bill may help some species produce bill-snapping sounds for communication in storms.
– Wing-clapping – Specialized wing feathers allow storm petrels to produce humming or clapping wing sounds in displays.
Functions of Storm Petrel Vocalizations
The diverse calls of storm petrels serve a variety of important functions:
– Maintaining contact – Calls allow storm petrels to remain in acoustic contact with flock-mates, pairs, or colonies in noisy, pelagic environments.
– Individual recognition – Mate recognition and individual identification is facilitated by unique call characteristics of each bird.
– Courtship displays – Purring, humming, and other displays advertise breeding condition and attract/bond mates.
– Coordinating activity – Shared calls synchronize activities like feeding, migration, landing and takeoff between colony or flock members.
– Defending territory – Screeching, snapping bills, and other calls establish territories and aid in colony settlement.
– Begging calls – Loud chick begging elicits feeding from parents. The rasping calls pinpoint locations in dense colonies.
– Predator warning – Alarm calls alert others to danger and may startle or distract predators.
– Signaling over wind and waves – Harsh calls carry farther over distance, allowing communication in stormy seas.
How Storms Affect Vocalizations
Stormy conditions significantly impact the vocal behavior of storm petrels:
– Higher call rates – Birds call more often in wind and rain to maintain flock cohesion. Call intervals decrease.
– More powerful calls – Storm petrels switch to louder, piercing cries more audible over wind and waves.
– Higher frequencies – Calls contain more high-frequency components to reduce degradation in wind.
– Rhythmic modulations – Birds rhythmically alter elements like frequency and amplitude to maintain signal transmission.
– Synchronized calling – Members of a flock synchronize their calls into communal chorusing to boost signal range.
– Closer spacing – Storm petrels fly closer together with reduced call intervals to preserve acoustic contact.
– Leeward flight – Birds alter flight paths to call while positioned leeward, providing sound shelter.
– Modified foraging – Feeding flocks are more cohesive and coordinated vocally in storms.
– Colony relocation – Breeding birds shift colony sites to more sheltered acoustical environments.
– Mate call duplication – Pairs converge their calls to reinforce mate recognition in wind and rain.
Unique Adaptations for Storm Communication
Storm petrels possess anatomical and behavioral adaptations that facilitate acoustic communication in stormy conditions:
– Syrinx muscles – Powerful syrinx muscles allow birds to produce louder, more sustained calls audible over wind and rain.
– Enlarged vocal tract – An elongated trachea and throat air sac boosts call amplitude and range.
– Directional bill – Their short, hooked bill gives calls directionality to reduce wind masking.
– Rictal glands – Glandular secretions help produce bill-snapping sounds detectable in storms.
– Dietary oils – Stomach oils likely impart water resistance to reduce wetting of the sound-producing syrinx.
– Dense waterproof plumage – A thick coat of feathers insulates birds from cold rains that could impact vocalizations.
– Wing-clapping – Clapping flight feathers allows an alternate signaling mode in high winds.
– Communal flocking – Flocks are very cohesive to facilitate acoustic monitoring of signals.
– Synchronized modulation – Call characteristics are modulated in unison to boost propagation.
– Nocturnal calling – Using darkness reduces visual separation while also minimizing wind effects.
How Storm Petrel Calls Are Studied
Researchers use various methods to study the sounds storm petrels produce:
– Field recordings – Microphones and recorders are placed in colonies to capture natural vocalizations.
– Auditory surveys – Observers note call characteristics, context, and behaviors during observations.
– Acoustic analysis – Computer programs visualize sounds and allow detailed quantification of features like frequency and amplitude.
– Playback trials – Recorded calls are played to induce behavioral responses that reveal call functions.
– Anatomical study – Dissections, endoscopy, MRIs and related techniques reveal the physical structures used to produce sounds.
– Acoustic modeling – Mathematical models simulate how weather conditions impact call propagation.
– Tracking – Tags record location to relate calls to movements and map calling hotspots.
– Neural imaging – Activity of brain regions linked to call perception/production is measured.
– Genetic analyses – Gene expression differences identify those linked to vocalizations.
– Comparative research – Related species are studied to determine shared vs. unique call features.
Remaining Questions About Storm Petrel Vocalizations
While much is known about storm petrel calls, some questions remain:
– Individual signatures – Do calls contain individually distinct identifiers? If so, how are they distinguished?
– Call development – How exactly do unique species-specific calls develop in young birds?
– Call categories – Can storm petrel calls be classified into distinct types based on context and meaning?
– Call dialects – Are there geographical vocal dialects between different populations?
– Evolution of storm calls – How did the specialized storm-related calls evolve? Were ancestral calls different?
– Neurological control – What brain regions control call production and modification? How is this coordinated?
– Offshore calling – Do vocalizations differ when birds are far offshore rather than near colonies?
– Effects of climate change – Will changing storm patterns alter vocal adaptations of storm petrels over time?
– Mechanisms of synchronized calling – How do flock members coordinate the timing of communal chorusing during storms?
– Relative importance of non-vocal sounds – How significant are bill snaps and wing claps compared to vocalizations?
Conclusion
The calls of storm petrels are incredibly varied and specialized for communicating over the booming surf and whipping winds they inhabit. Their vocal flexibility allows storm birds to coordinate their flocking, navigate, maintain pair bonds, and interact on breeding colonies despite the inhospitable conditions. Ongoing research continues to reveal the nuances of storm petrel communication and their evolutionary adaptations for life in the churning seas. Their unique noises provide insight into the pressures faced by pelagic species and the solutions evolution has produced to overcome these challenges. Storm petrel calls are sure to hold many remaining secrets about how animals communicate and thrive in some of the most acoustically difficult environments on Earth.
