Screech owls are known for their eerie, shrill calls in the night. Unlike the deep hoots of many other owl species, the vocalizations of screech owls are comprised of rhythmic, quavering trills. These trills serve several important purposes for these small raptors.
Screech owls produce trills for communicating with other screech owls. The trills help screech owls find mates, defend territories, warn of threats, and maintain contact with their mate or offspring. Additionally, the acoustic structure of screech owl trills is specially adapted for being localized by other screech owls.
Screech Owl Species
There are three species of screech owl found in North America:
- Eastern screech owl (Megascops asio)
- Western screech owl (Megascops kennicottii)
- Whiskered screech owl (Megascops trichopsis)
All three species produce similar-sounding trills, though there are some subtle differences between the calls of each species. The trills all serve the same core functions, however.
Finding Mates
One of the main reasons screech owls trill is to attract potential mates. Most screech owl mating activity occurs during late winter and early spring. When ready to breed, male screech owls will sing emphatically at night to proclaim territory ownership and attract females.
The male’s trilling song has a distinctive rhythm consisting of a long note followed by a trembling series of shorter notes. This song can be repeated hundreds of times throughout the night. Females who are interested in mating with the male may approach and duet with him.
Screech Owl Courtship
Once paired, the male and female screech owls enhance their bond through duets. The two owls perch close together and call back and forth to each other with trills. The vocal duets help the owls assess each other’s fitness for breeding.
After mating, the male will stay near the nest and continue to trill. His trilling helps the female locate the nest when returning from hunting at night. The male’s trills also serve to ward off rival males from his mate’s territory during breeding season.
Defending Territories
Screech owls are very territorial, and their haunting trills serve to proclaim territory ownership and warn away trespassers. A mated pair of screech owls will defend a territory of around one square mile in area.
When an intruding screech owl enters their domain, the resident owls will signal their presence through increased trilling. This helps avoid direct confrontations with territorial neighbors.
Both male and female screech owls participate in territorial defense. They often engage in counter-dueting, with each owl trying to vocally overpower the other. The resident owls almost always out-sing an intruder until it retreats back to its own territory.
Signals of Aggression
Screech owls use slight variations in their trilling to signal escalating levels of aggression toward intruders. Some of these threat signals include:
- Short, irregular pulses – mild warning
- Harsh, grating tones – moderate threat
- Faster trilling with shrill overtones – high alert
- Raspy screaming – extreme aggression and potential attack
By assessing the nuances of a neighbor’s territorial calls, screech owls can usually settle boundary disputes through vocal interactions alone, without actual combat.
Warning of Threats
Screech owl trills serve to warn other screech owls of danger. When approached by a potential predator like a hawk, screech owls will emit loud, urgent trilling. This alarms other screech owls, signaling them to take cover.
Both sexes and even young screech owls will trill to raise the alarm of threats. Adults are more vigilant and sensitive to danger than their offspring, providing early warning through their trills.
Screech owls also have different alarm calls depending on the type of threat detected. For ground predators like foxes, they use a bouncing, galloping trill. For aerial predators, they use a faster whinny-like trill.
Mobbing
A group of screech owls together can try to drive predators away through mobbing. This involves several owls perching close together and trilling loudly at an intruder. The cacophony of their threatening calls is meant to disorient and intimidate the unwanted visitor.
Sometimes other small bird species will join in mobbing with screech owls to help drive out a common predator. The presence of the larger owls helps make the mobbing effort more effective.
Staying in Contact
Screech owl pairs utilize trilling to help keep track of each other, especially when the female is nesting. The male will perch near the nesting cavity and trill regularly to reveal his location to his mate.
The female can also trill back to update the male on her progress after leaving the nest. The male’s frequent trilling helps guide the female back to the correct tree once she returns from hunting.
Parents trill near the nest to communicate with newly fledged chicks. The chicks give faint answering trills, allowing the adults to locate them and continue providing food.
Locating Other Screech Owls
Screech owl trills are specifically adapted to enable other screech owls to pinpoint the caller’s location. Their vocalizations have acoustic qualities that make the source easy to triangulate based on sound alone.
Acoustic Adaptations
Screech owl trills have the following acoustic qualities that enhance sound localization by receivers:
- Narrow frequency range – easier to distinguish from background noise
- Minimal frequency modulation – maintains signal clarity
- Short signal segments – avoids echo interference
- Steep amplitude modulations – improves distance estimation
These adaptations allow other screech owls to determine direction, distance, and identity of a trilling owl, even on dark nights in dense forests.
Ideal Volume
Screech owls trill at an ideal volume to be detected by other owls without being overly conspicuous to larger predators. The volume falls within 60 to 80 decibels measured at around 6 meters away.
This moderate volume allows their trills to be heard up to several hundred meters by other screech owls while avoiding detection by most mammals over 50 meters away.
Conclusion
The quavering, whinnying trills of screech owls serve several important functions related to communication, territoriality, alarming others of threats, and staying in contact. The acoustic qualities of the trills are specially adapted to facilitate localization by other members of the same species.
So the next time you hear a screech owl’s haunting trill in the night, you’ll know it is much more than just an eerie sound! The trills form a complex communication system essential to the daily and seasonal survival of these cryptic birds of prey.