Long-billed Curlews Eavesdrop on the Alarm Calls of Black-tailed Prairie Dogs

Many birds rely on visual and auditory cues to evaluate the risk of predation and decide how to respond defensively. When these cues originate from another species, “eavesdropping” becomes an important behavioural strategy. In the grassland ecosystems of the North American Great Plains, the long-billed curlew (Numenius americanus) is able to listen to the alarm calls of the black-tailed prairie dog (Cynomys ludovicianus) and react earlier to potential predators, thereby reducing the likelihood that its nest will be discovered. This form of interspecific eavesdropping illustrates how information can travel across species boundaries and also reframes the ecological role and conservation value of prairie dogs within these grassland communities.

Long-billed curlew（Image source：Ingrid Taylar， CC BY 2.0 ）

Black-tailed prairie dog（Image source：Musicaline， CC BY-SA 4.0 ）

Black-tailed prairie dogs produce alarm calls that distinguish between aerial and terrestrial predators. These signals are rapid, precise, and highly informative, providing effective warnings not only to other prairie dogs but also to nearby animals. A recent study proposed that long-billed curlews might use these alarm signals to evaluate predation risk and respond by adopting concealment behaviour earlier, thus reducing the chance that predators will locate their nests.

To test this idea, researchers conducted a series of field experiments between 2023 and 2024 in the grasslands of Montana, United States. They used a simulated terrestrial predator consisting of a taxidermized American badger (Taxidea taxus) mounted on a remote-controlled vehicle. The model predator was driven toward nests containing incubating curlews. In the treatment trials, recordings of prairie dog alarm calls associated with terrestrial predators were played, while in the control trials no alarm calls were broadcast. During each experiment, researchers recorded when the incubating female curlew adopted a cryptic posture—a defensive behaviour in which the bird lowers its body and head, pressing itself flat against the ground to avoid detection.

The results were clear. When prairie dog alarm calls were played, female curlews adopted the cryptic posture while the simulated predator was still farther from the nest. On average, they concealed themselves roughly 21 meters earlier than in trials without prairie dog alarm calls. This finding provides strong evidence that curlews are indeed eavesdropping on prairie dog warning signals. The alarm calls therefore function as cross-species information that helps curlews anticipate danger.

Interestingly, non-incubating male curlews did not alter their behaviour in response to prairie dog calls. Their rates of alarm calling and dive-bombing—a mobbing behaviour used to drive predators away—did not increase when prairie dog alarms were present. One possible explanation is that these conspicuous defensive actions may attract attention to the nest and are therefore not advantageous unless a predator is already very close.

This research represents the second documented case of birds eavesdropping on black-tailed prairie dog alarm calls. The first involved the burrowing owl (Athene cunicularia). More broadly, it provides a rare example of birds listening to warning signals produced by mammals. Most previously known cases of interspecific eavesdropping occur either between birds or between mammals. The study therefore expands our understanding of how communication networks operate within ecological communities.

Because these interactions can influence survival and reproduction, the black-tailed prairie dog may function as a “keystone information producer.” Prairie dog colonies generate large volumes of reliable information about predators through constant vigilance and frequent alarm calls. Other species can exploit this information to improve their own defensive behaviour.

Burrowing owl（Image source：Wagner Machado Carlos Lemes， CC BY 2.0 ）

Prairie dog colonies themselves are large social complexes formed by extensive burrow systems. These colonies often attract predators, making them areas of high predation activity. Yet many bird species still choose to nest or raise their young near prairie dog colonies. The ability to eavesdrop on prairie dog alarm calls may help explain this apparent paradox. Although predator activity is high, the constant flow of warning signals may reduce the actual risk experienced by birds.

The study also highlights conservation concerns. Both black-tailed prairie dogs and long-billed curlews face threats associated with human activity. Historically, prairie dog habitat has been dramatically reduced by agriculture and disease, leaving only about two percent of its original range. As colonies shrink and become fragmented, their ability to detect predators declines. Larger prairie dog groups can identify threats more quickly and produce more warning signals, whereas smaller populations weaken the overall flow of information across the ecosystem. Such changes could indirectly affect other species, including birds that depend on prairie dog alarm calls to detect predators.

If prairie dog populations continue to decline, the loss of these warning networks may reduce the reproductive success of species such as long-billed curlews and burrowing owls. Understanding these subtle ecological connections therefore becomes essential for effective grassland conservation.

Author: Shui-Ye You

Reference:

Dreelin RA et al. (2025). Interspecific eavesdropping by birds on a keystone mammal improves antipredator behaviour. Animal Behaviour.