Parent-absent begging in the Brown-headed Cowbird (Molothrus ater): the role of short-term need and nestmate size

Abstract

Although it is well-established that nestlings of many altricial species beg when parents are away from the nest, we have a poor understanding of parent-absent begging in brood parasites, including the proximate factors that may influence begging frequency and intensity. In this study, I examined how parent-absent begging was influenced by competitive asymmetries between host and Brown-headed Cowbird (Molothrus ater) nestlings under disparate levels of short-term need. Food-deprived cowbird nestlings begged more frequently and for a greater proportion of parent-absent period than when food-supplemented, with similar patterns observed in hosts of different sizes. In contrast, three metrics of cowbird begging intensity varied relative to host size but not due to differences in short-term need. Cowbirds consistently begged more frequently and intensively than host nestlings for a given level of short-term need, providing evidence that cowbird begging displays are more frequent and intense than non-parasitic nestlings during both feeding visits and parent-absent periods. In sum, the frequency of begging by cowbirds was only influenced by short-term need, whereas begging intensity during parent-absent events was only influenced by the host against which cowbirds competed. This study demonstrates that host size and shortterm need had differing influences on the frequency and intensity of parent-absent begging in cowbirds, although both factors are likely important in limiting the evolution of parent-absent begging in cowbirds. Because it appears to provide no immediate benefits yet may decrease fitness, parent-absent begging should be included in future theoretical models investigating the evolution of begging displays in nestling birds.

Great spotted cuckoos respond earlier to the arrival of feeding foster parents and perform less erroneous begging when hungry than their magpie host nest‐mates

“…As far as we know, the great spotted cuckoo is the first cuckoo species in which the frequency of erroneous begging did not increase under restricted food conditions. Brown‐headed cowbirds showed also a more rapid response to an approaching foster parent than host nestlings, but they also presented a higher rate of mistaken responses (Rivers ).…”

“…Statistical analyses were performed with RStudio (ver. 1.0.153, –2017 RStudio). Data used in this study, both in the lab experiment and in natural nests are included in Supplementary material Appendix 1.…”

“…Begging signals are emitted by nestlings to solicit food from their parents and are considered to be honest signals because they entail several physiological costs (Kilner , Noguera et al , Martín‐Gálvez et al , Moreno‐Rueda and Redondo , Soler et al ). Consequently, parents regulate their effort and resource allocation according to the conspicuousness and intensity of the begging displays (Price and Ydenberg , Kilner and Johnstone , Budden and Wright , Leonard and Horn , Quillfeldt et al , Budden and Beissinger , Martín‐Gálvez et al , Ruiz‐Castellano et al ). As such, parents often preferentially feed the nestlings with the most intensive begging displays (Dearborn , Lichtenstein and Sealy , Leonard et al , Roulin et al , Hauber et al , Leonard and Horn , Roulin ), but also the first nestling that starts to beg is usually fed before its nest‐mates (Roulin , Leonard et al , Porkert and Spinka ).…”

“…Begging by mistake not only incurs a physiological cost, but more importantly, conspicuous begging signals increase the risk of nest predation (Haskell , Leech and Leonard , McDonald et al , Haff and Magrath , Ibáñez‐Álamo et al ). It is evidently in the interest of both parents and nestlings to avoid nest predation, which is likely to have been a driving factor in the evolution of begging vocalizations.…”

Sexual Differences in Parental Investment in Response to Parent‐Absent Calls

“…Firstly, most of these calls have been attributed to parent‐absent begging (or begging errors ) behaviour, which is associated with false alarms or cognitive fails, and comprise long, loud, broad frequency vocalizations, identical to those showed during parental visits (Budden & Wright ; Leonard & Horn ; Dor et al. ; Rivers ). Secondly, nestlings of some other species perform shorter, quieter repeat calls, with a much narrower sound frequency and generally less detectable (Roulin et al.…”