Is it interspecific information use or aggression between putative competitors that steers the selection of nest-site characteristics? A reply to Slagsvold and Wiebe.

Forsman, Jukka; Seppänen, Janne-Tuomas; Monkkonen, Mikko; Thomson, Robert; Kivelä, Sami; Krams, Indrikis; Loukola, Olli

27 November 2017

A growing number of studies have demonstrated that heterospecific individuals with overlapping resource needs – putative competitors – can provide information to each other that improves the outcomes of decisions. Our studies using cavity nesting resident tits (information provider) and migratory flycatchers (Ficedula spp., information user) have shown that Selective Interspecific Information Use (SIIU) can result in flycatchers copying and rejecting the apparent nest-site feature preferences of tits, depending on a perceivable fitness correlate (clutch size) of the tits. These, and other results on the interspecific information use, challenge the predictions of traditional theory of species coexistence. Recently, Slagsvold and Wiebe (2017) proposed an alternative hypothesis, the Owner Aggression Hypothesis (OAH), to explain our results. Their main points of critique are: 1) a lack of evidence that flycatchers make visits into tit nests prior to nesting and 2) flycatchers do not have an ability to assess tit clutch size. According to Slagsvold and Wiebe, interspecific aggression between tits and flycatchers, not information use, is the mechanism explaining our results. In this reply we show that part of Slagsvold and Wiebe’s criticism is based on mischaracterization of the assumptions of SIIU, resulting in misinterpretations of our results. We also provide new evidence that flycatchers (mostly males) frequently visit tit nests prior to settlement and can acquire information about tit clutch size and thereby on the quality of the tutoring tit individual and its decisions. In short, as intriguing as OAH is, we suggest that 1) some of the assumptions are highly speculative and lack evidence, while 2) our earlier experiment (Loukola et al. 2013) has clearly demonstrated the importance of the visible clutch size of tits for flycatcher decisions. Therefore, SIIU can more parsimoniously than OAH explain the behaviour of flycatchers.