Feather mite abundance varies but symbiotic nature of mite‐host relationship does not differ between two ecologically dissimilar warblers

Abstract

Feather mites are obligatory ectosymbionts of birds that primarily feed on the oily secretions from the uropygial gland. Feather mite abundance varies within and among host species and has various effects on host condition and fitness, but there is little consensus on factors that drive variation of this symbiotic system. We tested hypotheses regarding how within‐species and among‐species traits explain variation in both (1) mite abundance and (2) relationships between mite abundance and host body condition and components of host fitness (reproductive performance and apparent annual survival). We focused on two closely related (Parulidae), but ecologically distinct, species: Setophaga cerulea (Cerulean Warbler), a canopy dwelling open‐cup nester, and Protonotaria citrea (Prothonotary Warbler), an understory dwelling, cavity nester. We predicted that feather mites would be more abundant on and have a more parasitic relationship with P. citrea, and within P. citrea, females and older individuals would harbor greater mite abundances. We captured, took body measurements, quantified feather mite abundance on individuals’ primaries and rectrices, and monitored individuals and their nests to estimate fitness. Feather mite abundance differed by species, but in the opposite direction of our prediction. There was no relationship between mite abundance and any measure of body condition or fitness for either species or sex (also contrary to our predictions). Our results suggest that species biology and ecological context may influence mite abundance on hosts. However, this pattern does not extend to differential effects of mites on measures of host body condition or fitness.

From unwanted squatters to good tenants: Ectosymbionts and their relationships with body condition of Atlantic Forest Passeriformes

“…2014; Matthews et al . 2018), which could also explain the high mite loads we found. Regarding ectoparasites, chiggers and ticks are not exclusive parasites of birds or may be parasitic only in specific life cycle phases (Dietsch 2005; Storni et al .…”

“…2001; Proctor 2003; Matthews et al . 2018). A commensal relationship could be the reason for the lack of a significant relationship between feather mite load and morphological traits of the bird species we studied.…”

Darwin’s finches habitually anoint their feathers with leaves of the endemic treePsidium galapageiumduring the non‐breeding season

“…Species in the four bottom rows were excluded from the analysis because they were never or only once observed to preen with leaves (Gaede & Knülle, 1987); however, in our study area, the RH was always well above this value in both seasons. In addition, most feather mites do not negatively impact birds (Dowling et al, 2001;Matthews et al, 2018), rather they have a mutualistic relationship with their host, cleansing the birds' feathers from fungi and bacteria (Doña et al, 2019). Villa et al, (2013) did find very small numbers of blood-feeding mites (Pellonyssus sp.)…”

Differential survival and dispersal of avian feather mites with contrasting host specificities

“…Once in hand, we inspected birds for feather mites and then collected one tail feather (that harboured mites) in an individual glassine envelope. Because mite abundances can vary greatly by individual feather, we attempted to collect feathers that allowed us to capture much of the natural variation in mite abundance that exists (Matthews et al, 2018, T.J.B., unpublished data). Thus, by doing so, we were able to account for the possibility that mite abundance (and competition) may influence either dispersal or survival of mites.…”