Belfín, O., Kempenaers, B. and Piersma, T. (2024), Daily and seasonal use of vocalizations by nesting black-tailed godwits. J Avian Biol e03362. https://doi.org/10.1111/jav.03362

In the grasslands of a Dutch dairy farm, black-tailed godwits (Limosa limosa limosa) communicate at their nests in ways that balance the need for coordination with partners and young with the risk of attracting predators. We used passive acoustic recorders to continuously monitor eight nests throughout the entire incubation period, offering new insights into their communication strategies. Conducted on a farm with one of the highest breeding densities of godwits in the Netherlands, we collected over 4,000 hours of audio data to capture the full range of godwit vocalizations. To analyze this extensive dataset, we used machine learning to process over 70,000 godwit calls, demonstrating how digital tools can help manage large datasets and reveal new details in behavioural studies.

We identified five main call types used by godwits at the nest. Each call type had a distinct purpose and structure, suggesting a range of communication strategies at play. The types included loud alarms, territorial calls and calls used possibly for intra-pair communication, quieter calls for near-nest communication, and calls with less obvious functions. Some of the calls could likely be further separated to reflect more subtle differences.

Summary of five main call types

Contrary to our expectations, godwits often used loud calls even at the nest, potentially increasing their risk of predator detection. However, these loud calls were largely limited to daylight hours when predators were easier to spot, with calling activity dropping off significantly at night. Interestingly, godwits used more calls on moonlit nights, possibly taking advantage of increased visibility to communicate with less risk. 

One particularly puzzling behaviour was the use of short and harsh calls early in the incubation period, often without any obvious receiver. These quiet calls did not seem directed toward mates or nearby chicks, raising questions about their purpose. We speculated about their meaning, but their exact function remains unclear and invites further study.

Godwits also showed big differences in alarm-calling behaviour among individual nests. While the nests shared similar predator pressures, some nests (godwits) were far more prone to give alarm calls than others. This variability suggests that factors such as individuality, nest placement, or social influences may affect calling behaviour, opening up interesting avenues for future research on individual communication strategies within the broader community of breeding birds.

Another key finding was related to godwits’ behaviour in leaving the nest. The likelihood of a godwit leaving the nest increased significantly when multiple godwits gave alarm calls nearby, especially actively mobbing a predator. The probability of leaving rose in a quadratic relationship with the number of alarm calls, suggesting that godwits rely on acoustic cues from neighbouring birds to accurately estimate the threat level.

Sixty years after Hans Lind’s first and definitive study of breeding behaviour (including vocalizations) of black-tailed godwits at Tipperne, southern Jutland, Denmark, we could make the next step using the latest technology advances and show how godwits use vocal strategies to communicate effectively within a community of breeding birds while remaining cautious of predators. These findings open new ways for more studies to explore if similar vocal adaptations exist across other shorebird species and habitats, potentially offering a broader understanding of how avian species balance social interaction with predation risks.

Text and photo:
Ondřej Belfín