Animals use varied acoustic signals that play critical roles in their lives. Understanding the function of these signals may inform about key life-history processes relevant for conservation. In the case of fin whales (Balaenoptera physalus), that produce different call types associated with different behaviours, several hypotheses have emerged regarding call function, but the topic still remains in its infancy. Here, we investigate the potential function of two fin whale vocalizations, the song-forming 20-Hz call and the 40-Hz call, by examining their production in relation to season, year and prey biomass. Our results showed that the production of 20-Hz calls was strongly influenced by season, with a clear peak during the breeding months, and secondarily by year, likely due to changes in whale abundance. These results support the reproductive function of the 20-Hz song used as an acoustic display. Conversely, season and year had no effect on variation in 40-Hz calling rates, but prey biomass did. This is the first study linking 40-Hz call activity to prey biomass, supporting the previously suggested food-associated function of this call. Understanding the functions of animal signals can help identifying functional habitats and predict the negative effects of human activities with important implications for conservation.

Acoustic dataset were collected by using bottom fixed autonomous recordings, specifically Ecological Acoustic Recorders. Recordings were then processed automatically for the detection of the  20-Hz call or manually for the 40-Hz call. A call rate index was calculated per week (number of calls / time of recording)  and then compared to weekly simulated zooplankton biomass.

Dataset called: weekly_fin_nosum.csv include weekly call rate index for each call type (20-Hz and 40-Hz) and the corresponding simulated zooplankton biomass. This dataset is then used in the R code supplied for modelling through Generalised linear models. The code is self-explanatory.

Dataset called: fin_month_year.csv includes call rate index for the two call types and is used for the code to create figure 2A & B.

Dataset called: all_prey.csv includes weekly simulated prey biomass that is used for the code to create Fig. 2C.