Red-necked Falcons Falco chicquera track changing environments by shifting their trophic niche during the rainy monsoon season

Capsule
Red-necked Falcons Falco chicquera shift their trophic niche, from eating birds to bats, during the rainy monsoon season.

Aims
To explore seasonal changes in prey weight, diet composition, and mobbing interactions of the globally Near Threatened Red-necked Falcon in Bangladesh.

Methods
We analysed long-term direct observations of 19 adult pairs feeding on prey between 2002 and 2019, exploring changes in mean prey weight, prey group, and mobbing interactions throughout the cool dry winter, hot pre-monsoon, and rainy monsoon seasons.

Results
The probability of bats being present within the diet increased over time, from 16% in the cool dry winter and 11% in the pre-monsoon hot season, to 48% in the rainy monsoon season. This coincided with a significant decline in mean prey weight and biomass consumed during the rainy monsoon season. Probabilities of falcons being mobbed during feeding varied throughout the seasons, depending on mobbing species.

Conclusion
Red-necked Falcons appeared to track changing environments by shifting their trophic niche during the rainy monsoon season. This may be due to: (a) an optimal foraging response to bat population fluxes, itself a response to weather-induced increases in flying insect abundances, (b) opportunistic hunting of bats during periods of crepuscular activity peaks, and/or (c) the energetic demands of fledglings during the rainy monsoon season.