On resolving the selective interspecific information use vs. owner aggression hypothesis dilemma—a commentary

Abstract

Using information acquired from other individuals (social information use) is ubiquitous in animals and not restricted to withinspecies context. Some of the textbook examples of interspecific information use in the wild has been provided using apparent novel niche experiment approach, with migratory flycatcher species (Ficedula spp.) cueing on apparent nest site preferences (geometric symbols) and clutch sizes of resident great tits (Parus major) and blue tits (Cyanistes caeruleus) to choose their own nest site. However, the interpretation of these results has recently been challenged. It has been argued that there is no evidence that flycatchers visit tit nests to collect information about clutch size or that flycatchers are capable of Bcounting^tit eggs. Instead, it has been proposed that the decision-making patterns of flycatchers found in earlier studies resulted from aggressive interactions, not information use, between tits and flycatchers (termed owner aggression hypothesis). Here, I contribute to the debate around both hypotheses and specifically explore the remaining points of disagreement, related to the timing of flycatchers prospecting and the cognitive abilities needed to assess tit clutch size. I argue how interannual variation in phenology can explain the apparent discrepancy between the observed and predicted timing of flycatchers prospecting. I also argue why assessing tit clutch size neither requires Bcounting^eggs nor any sophisticated cognitive capacities. Finally, I propose experimental designs to test the hypotheses on the underlying mechanisms explaining the observed patterns, which will allow taking further leaps in resolving the selective interspecific information use vs. owner aggression hypothesis dilemma.

No evidence that nest site choice in Pied Flycatchers is mediated by assessing the clutch size of a heterospecific, the Great Tit

“…Furthermore, the strong annual variation in Great Tit clutch size (up to 1.6 eggs on average between two breeding seasons) means that several tit nests would need to be visited within a breeding season for a prospecting flycatcher to be able to assess whether a tit clutch is relatively small or large but data show that male and female Pied Flycatchers visit few nest cavities before settling (Slagsvold 1986;Dale and Slagsvold 1996). The SIIU hypothesis predicts that it may be difficult for prospecting flycatchers to use tit clutch size as a cue in years when flycatchers arrive and settle early after migration when many tits may not yet have initiated or completed their clutches (Morinay et al 2018;Szymkowiak 2019). However, in our study, the peak period of flycatcher arrival and settlement occurred when we filmed the tit nests, so a lack of active tit nests cannot explain the scarcity of entrances by flycatchers.…”

“…This version of the SIIU hypothesis has received much focus within a model system of migrant Pied Flycatchers Ficedula hypoleuca and resident Great Tits Parus major (Avarguès-Weber et al 2013;Aplin 2016;Szymkowiak 2019), but we recently pointed out that its acceptance is premature because the mechanism by which one species of bird supposedly assesses the clutch and brood size of another has not been well articulated or studied. We also questioned the adaptive significance of copying the external markings around cavity entrances when choosing nest sites Wiebe 2017, 2018).…”