# Supernormal Stimulus Begging Calls of Brood‐Parasitic Nestlings Depress the Parental Care in an Uncommon Host

## TL;DR

Brood-parasitic cuckoo nestlings use exaggerated begging calls to manipulate host parents, but these calls may not work well with uncommon hosts like Barn Swallows.

## Contribution

The study reveals that cuckoo begging calls, though effective on common hosts, can reduce parental care in uncommon hosts like Barn Swallows.

## Key findings

- Male Barn Swallows decreased feeding frequency in response to cuckoo nestling calls.
- Female Barn Swallows reduced feeding frequency only when cuckoo calls were from common hosts.
- Environmental factors like brood size and weather also influenced feeding behavior.

## Abstract

During the nestling period, brood‐parasitic birds stimulate host parents to provide food through complex visual and auditory signals, including emitting supernormal stimuli in the form of begging calls to increase the feeding frequency. However, whether the begging calls of brood‐parasitic nestlings act as a universal type of supernormal stimulus signal and their effects on less common host species still require further research. In this study, we used playback recordings to verify the impact of the begging calls of Common Cuckoo (
Cuculus canorus
) nestlings on the parental care behavior of host Barn Swallow (
Hirundo rustica
) parents. Contrary to our expectations, the results showed that male Barn Swallow parents decreased their feeding frequency in response to both types of Common Cuckoo nestling calls (cuckoo nestlings reared by the Oriental Reed Warbler
Acrocephalus orientalis
/the Barn Swallow), while females decreased their feeding frequency in response to the begging calls of Common Cuckoo nestlings reared by the common host (the Oriental Reed Warbler). Additionally, brood size, temperature, and weather all affected the feeding frequency in the Barn Swallow. This study supports the idea that the supernormal stimulus of brood‐parasitic nestling begging calls does not always work as a universal signal; the behavioral adaptations formed by parasitic birds in response to common hosts may lead to reduced fitness when utilizing uncommon hosts, for example, the Barn Swallow.

The exaggerated begging calls of brood‐parasitic nestlings, for example, the Common Cuckoo, could serve as a supernormal stimulus to the host parents, but their effectiveness in uncommon host species remains unclear. In this study, we tested the effect of cuckoo nesting begging calls on an uncommon host species, the Barn Swallow, with manipulative playback experiments. Contrary to our expectations, we found that male Barn Swallows significantly reduced their feeding frequency in response to cuckoo nestling calls, suggesting that this signal inhibited parental investment in a less common host species.