Cuckoos are well known for their distinctive and loud “cuckoo” call. This call is made mostly by male cuckoos and serves several important purposes related to breeding, territory defense, and signaling to females.
Cuckoo Calls Signal Territory
Male cuckoos establish breeding territories each spring when they arrive back from migration. Their loud “cuckoo” calls are one of the main ways they advertise their territory to other male cuckoos. Calling loudly and frequently signals that a territory is occupied and warns other males to stay away.
Cuckoos are fiercely territorial and will aggressively chase away intruders, so frequent calling reduces physical confrontations. Loud calls also allow male cuckoos to estimate how many rivals may be present nearby based on how many other individuals they hear calling. Calling more often when lots of competitors are around may help strengthen a male’s territorial claim.
Calls Attract Females
In addition to warding off rival males, the frequent “cuckoo” calls of male cuckoos also help attract females. The distinctive call allows females to easily locate potential mates within their breeding range.
Males often call most vigorously in the morning and evening when females are most receptive to mating. Producing loud, repetitive calls increases a male’s chances of encountering and mating with females as they pass through his territory.
Signaling Fitness to Females
Calling takes energy and requires good respiratory health, so the ability of male cuckoos to produce loud, persistent calls may also signal their physical fitness. Females likely prefer males that can sustain calling for long periods as it may indicate better health, strength, and vitality.
Some research indicates that female cuckoos preferentially respond to calls that have a higher peak frequency. This ability to produce higher pitched calls may correlate with male quality or fitness.
Defending Nest Sites
In some cuckoo species like the Oriental cuckoo, males continue calling after females begin incubating eggs. At this stage, calling primarily serves to defend the nesting site. Loud calls warn rival males away from the area and announce that the territory is occupied.
Persistent calling also allows the female to monitor her mate’s continued presence and commitment to the nest site while she is incubating. If the male stops calling for prolonged periods, the female may abandon the nest to find a new mate.
Advertising to Potential Hosts
For cuckoo species that lay their eggs in the nests of other birds, loud calling by males may help attract the attention of potential hosts. Some research suggests certain cuckoo species have evolved calls that specifically mimic the calls of certain host species.
This may lure host birds to investigate the call and make them more likely to encounter the female cuckoo and have their nest parasitized. However, more research is still needed to understand if call mimicry is intentional or just an incidental effect.
Warding Off Predators
Loud, repetitive cuckoo calls may also help deter potential predators from key nesting and foraging sites. Many bird species use mobbing calls to recruit others to help harass predators and drive them away from an area. Cuckoo calls may play a similar role in distracting predators or signaling an aggressive defense if disturbed.
Group Calling Facilitates Migration
Cuckoos migrate in loose groups between their breeding and wintering grounds. Frequent contact calling as they travel helps keep the group together and coordinates movement patterns. Hearing familiar calls from conspecifics also provides reassurance when migrating through unfamiliar terrain.
How Do Cuckoos Call So Much?
Cuckoos are able to produce their loud, repetitive calls thanks to specialized anatomical adaptations:
- Large syrinx – The vocal organ of birds located at the branch point between the trachea and bronchi. Cuckoos have an enlarged syrinx compared to many other birds.
- Reinforced trachea – Their trachea is reinforced with firm cartilage rings which support powerful vocalizations.
- Enlarged air sacs – Air sacs connected to the lungs provide an additional air reservoir for continuous calling.
- Strong abdominal muscles – Abdominal muscles connected to the syrinx control airflow and vocalizations.
These adaptations allow male cuckoos to produce their distinctive “cuckoo” song hundreds or even thousands of times per day during the breeding season. The high volume and persistence of their calling underlies its importance in territory defense and mate attraction.
How Often do Cuckoos Call?
The calling frequency of cuckoos varies by species, time of day, and stage of the breeding season. On average though, male cuckoos call very often:
- Common cuckoos – ~300 “cuckoo” calls per hour at dawn and dusk
- Yellow-billed cuckoos – ~1,200 calls per day
- Eastern koels – Up to 3,000 calls per day
Calling reaches its peak in the morning when females are laying eggs, and slows down after females begin incubating eggs. But males continue calling regularly until the end of the breeding season.
When are Cuckoo Calls Most Frequent?
Breeding Stage | Calling Frequency |
---|---|
Territory establishment | Moderate to high |
Female fertility period | Very high |
Egg laying | Very high |
Incubation | Moderate |
Nesting | Moderate |
Fledging | Low |
Calling peaks when female cuckoos are most receptive to mating and then again during peak egg laying. Calling continues at a reduced level through the rest of the breeding season.
How Do Cuckoo Calls Differ By Species?
While all cuckoo species produce a variation of the familiar two-note “cuckoo” call, details like frequency, pitch, tempo, and rhythm vary across the family’s 140+ species. Some examples:
- Common cuckoo – Distinctive descending minor third “cuck-oo”
- Yellow-billed cuckoo – Rapid series of double notes “cuc-cuc-cuc-cuc”
- Pheasant cuckoo – Melodic repetitive trill “cooroocoodleoo”
- Diederik cuckoo – Accelerating series of paired notes
- Greater coucal – Tuneful, bubbling song “doo-doo-doo”
Changes in Calling Over the Season
Most cuckoo species exhibit distinct seasonal changes in their vocalizations that correspond to breeding activities:
- Early season – Simple, repetitive contact calls to establish territory
- Courtship – Elaborate, melodic, variable calls to attract females
- Nesting period – Loud, persistent contact calls for territorial defense
- Fledging – Softer, infrequent calls only as needed
This flexibility allows the calls to effectively serve different purposes as the breeding season progresses from territory establishment to chick rearing.
Regional Dialects in Calls
Like many bird species, neighboring populations of some cuckoo species exhibit local differences in the details of their calls. These regional “dialects” arise when birds mimic the calls they hear locally, leading to gradual divergence between geographically separated groups.
Studies of common cuckoos in Europe have revealed measurable differences in the pitch, tempo, and frequency patterns of cuckoo calls in different countries. Local dialects have also been documented in Himalayan cuckoos and yellow-billed cuckoos.
The function of these dialects is not fully clear but may relate to local adaptation or signaling regional identity. More research is needed to understand how dialects arise and persist in cuckoo populations.
Mimicry of Host Species
Several parasitic cuckoo species exhibit call mimcry of their hosts’ vocalizations. For example:
- Common cuckoos mimic mewling buzzard calls
- Great spotted cuckoos mimic pied babbler calls
- Indian cuckoos mimic drongo calls
This acoustic mimicry may enable cuckoos to manipulate host behavior. Hosts may investigate the familiar calls and be more likely to encounter the cuckoo near their nest. However, more studies are needed to determine if mimicry is an intentional adaptation or just an incidental byproduct.
Do Cuckoo Calls Change Over Lifespan?
There are a few key ways cuckoo vocalizations change over the bird’s lifetime:
- Hatchlings – Begging calls to solicit food from parents
- Fledglings – Softer, less melodic version of adult calls while practicing
- Juveniles – Gradual development of full adult vocal range
- Adults – Seasonal changes in calling tied to breeding activities
- Aged adults – Slight atrophy and degraded quality of calls
Like other skills, cuckoo fledglings must practice their species’ distinctive calls, starting with a cruder version and gradually improving vocal control and complexity. As adults age, their calls may weaken or lose some elements.
Why Don’t Female Cuckoos Call?
In most cuckoo species, only the males produce the loud, repetitive territorial and courtship calls. There are a few reasons for this:
- Females devote energy to laying eggs rather than calling
- Calling could reveal the female’s presence to hosts (for parasitic species)
- Loud calls could attract predators to nest sites
- Frequent calling may be physiologically difficult for egg-bearing females
Instead, female vocalizations are typically limited to softer contact calls, food begging calls to elicit feeding from the male, and alarm calls when threatened. In a few tropical cuckoo species, females do participate in melodious duetting vocalizations with males.
Threats to Cuckoos from Calling
While loud, frequent calls are essential for breeding, they do pose some risks for cuckoos:
- Energy expenditure – Calling requires extra food consumption
- Predator exposure – Noise may attract predators
- Physical strain – Possible fatigue or injury of vocal tract
- Host alert – Calls could reveal nest sites to parasites hosts
However, the reproductive benefits of calling clearly outweigh these costs. Male cuckoos have evolved adaptations to sustain vigorous calling while minimizing risks.
How Do Ornithologists Study Cuckoo Calls?
Ornithologists use several methods to study the calling behaviors of wild cuckoos:
- Field observation – Directly monitoring and recording calls
- Audio recordings – Capturing calls for detailed acoustic analysis
- Statistical modeling – Quantifying factors influencing call rate
- Physiological studies – Measuring energy use during calling
- Playback experiments – Broadcasting calls and observing responses
- Comparative studies – Contrasting related species
Analyzing characteristics like call frequency, amplitude, pitch, and syntax provides insights into the ecological functions and evolution of cuckoo vocalizations.
Summary and Conclusions
In summary, cuckoos are prolific callers due to the importance of their loud, repetitive vocalizations for:
- Attracting mates
- Defending territories
- Communicating during migration
- Manipulating host behavior (for brood parasites)
Anatomical adaptations like an enlarged syrinx and reinforced trachea allow males to call hundreds or thousands of times per day. Calling peaks when females are most fertile but continues through the breeding season.
The familiar two-note “cuckoo” call exhibits remarkable diversity across the family’s many species in factors like pitch, tempo, and rhythm. Regional dialects and seasonal changes further reflect the nuanced functions calling plays across various contexts.
While essential for reproduction, frequent calling is not without costs for cuckoos. However, the benefits clearly outweigh the risks. The persistent vocalizations of cuckoos will likely continue to evoke images of spring for countless generations to come.