Who is in the neighborhood? Conspecific and heterospecific responses to perceived density for breeding habitat selection

Abstract

Theoretical models of habitat selection often incorporate negative density dependence. Despite strong negative density‐dependent effects on habitat selection, more recent studies indicate that animals settle near members of their own (conspecific) and other species (heterospecific) when selecting habitat with social cues. Social cue use for habitat selection is particularly common among songbirds, but few studies have investigated if songbirds use social cues to assess conspecific or heterospecific density (as opposed to just presence/absence) when making settlement decisions. We conducted a playback experiment to evaluate if yellow warblers (Setophaga petechia) and willow flycatchers (Empidonax traillii), two potential competitors for breeding habitat, use social cues to assess density (conspecific for warblers and heterospecific for flycatchers) when selecting breeding locations at two spatial scales. We simulated yellow warbler density to be high or low at multiple treatment plots (3.14 ha) with song playback and then evaluated settlement decisions by comparing yellow warbler and willow flycatcher abundances across plots (broad‐scale habitat selection) and individual space use within plots (fine‐scale territory establishment). Yellow warbler density treatments did not affect habitat selection by yellow warblers at the broad scale, but caused individuals to cluster territories at high‐density treatments. Willow flycatchers were most abundant at high‐density treatment plots, but yellow warbler density treatments did not affect territory locations. The results indicate that perceived density affects the habitat selection process for both conspecifics and heterospecifics.

Pairing status moderates both the production of and responses to anti‐parasitic referential alarm calls in male yellow warblers

“…), dogwood ( Cornus spp. ), and autumn olive ( Elaeagnus umbellate ), with mesic grasses abundant among shrubs (Kelly, 2017; Kelly et al., 2018; Lawson et al., 2020). Yellow warblers arrive at our sites in late April and breed from early May through late June, with a peak and synchronous period of breeding during mid‐to‐late May (Kelly et al., 2019; Lawson et al., 2020).…”

“…During visits, we followed each male at the site for 30 min on at least two separate, sequential trips and noted any mate‐guarding, a behavior commonly used to assign pairing status in Parulidae warblers, where males closely follow their mate while she is laying (e.g., yellow warblers: Hobson & Sealy, 1989b; other Parulidae: Chuang‐Dobbs et al., 2001; Stutchbury et al., 1994; Toms, 2012). We also searched male territories (within 30 m of male's song perch, the average size of a yellow warbler territory in central Illinois; Kelly et al., 2018) for active nests and/or a females exhibiting nest defense behaviors (alarm‐calling, perch‐switching, wing‐flicking, circle‐flight), which have been used to assign pairing status in similar studies (Ficken & Ficken, 1965; Hobson & Sealy, 1989b; Marshall & Balda, 1974; Mitra, 1999).…”

Heterospecific eavesdropping on an anti-parasitic referential alarm call

“…obs.). At our sites, redwings arrive as early as February and nest from late-April through late-July, with peak breeding in late-May 50,51 (pers. obs).…”

A review of conspecific attraction for habitat selection across taxa

“…Moreover, the cost of competition could preclude some individuals from using conspecific cues in high‐density locations, such as less competitive juveniles (sensu Szymkowiak et al., 2016). Surprisingly, few studies take conspecific cues revealing density into account (Kelly et al., 2018, and references therein), as most studies provide a cue that simulates one individual present at the treatment site. Fewer still compare the costs/benefits accrued by conspecific cue users to nonusers (Grendelmeier et al., 2017), making it difficult to evaluate whether conspecific attraction is an adaptive habitat selection strategy actually shaped by density dependence.…”