Abstract
ABSTRACTAcoustic signals play a key role in animal communication. Animals usually use alarm signals to warn mates or offspring of the presence of threats or to intimidate or distract predators. Birds commonly use acoustic signals as a means of communication. Alarm calls in passerines at different breeding stages can reflect their nest defense intensity. However, little is known about the characteristics, plasticity, and impact factors of alarm calls during the reproductive period in raptors. Here, from March to July in 2019, the alarm calls of eight pairs of common kestrels (Falco tinnunculus) during the breeding period were recorded using a portable recorder with a strongly directed microphone in the Zuojia Nature Reserve, Jilin province, China. The differences in acoustic parameters of parental alarm calls in different breeding stages were analyzed. The results showed that the alarm calls of common kestrels were composed of multi-harmonic arched frequency modulation with the maximum energy distribution in the second harmonic. The duration and rate of the alarm calls increased significantly as the breeding season progressed, showing that parents spent increasing amounts of time on nest defense. Additionally, the acoustic parameters of alarm calls in common kestrels were significantly different depending on offspring numbers, suggesting that offspring numbers influenced parental nest defense. These results showed that differences in alarm calls during different breeding stages may reflect a trade-off between defense costs and reproductive benefits.
Highlights
Acoustic signals play a key role in animal communication, such as in mate selection, resource defense, and individual or species recognition (Marler and Slabbekoorn, 2004; Wilkins et al, 2013)
The goals of this study were (1) to describe the characteristics of alarm calls in common kestrels; (2) to examine how parental alarm calls vary with the growth of offspring during different breeding stages; and (3) to assess whether offspring number affects parental alarm calls
The characteristics of alarm calls during the breeding period In this study, the alarm calls of common kestrels were characterized by loud, wide-band calls and were composed of multi-harmonic
Summary
Acoustic signals play a key role in animal communication, such as in mate selection, resource defense, and individual or species recognition (Marler and Slabbekoorn, 2004; Wilkins et al, 2013). Many birds and mammals produce alarm signals to warn of danger or the presence of predators (Caro and Girling, 2005; Fasanella and Fernández, 2009). Birds use alarm calls to inform and deter predators (Courter and Ritchison, 2010; Greig-Smith, 1980), or to prompt nestlings to adopt antipredation behaviors (McIntyre et al, 2014). Alarm calls in some bird species convey rich information about the type and size of the predators or the level of threat (Shah et al, 2015; Suzuki, 2014; Templeton et al, 2005). Alarm calls can provide crucial information in high-risk situations and have been shown to reduce the likelihood of birds being killed by a predator (Griesser, 2013)
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