Island biodiversity theory predicts that larger islands should support a greater diversity of species, both because of greater area and likely greater variation in habitats. Similarly, one might expect large-bodied animals to host a greater diversity of symbionts than small-bodied ones. We tested this prediction by looking at species richness of feather mites (Astigmata: Analgoidea, Pterolichoidea) recorded from birds of the order Charadriiformes, which range in body mass from 23 g for the Little Stint to 1.9 kg for the Brown Skua. We compiled charadriiform-host records from a literature database of more than 700 publications. Unexpectedly, the relationship between host body mass and mite richness showed a negative triangular distribution, with both mean and range of mite richness declining as host body mass increased. After investigating possible biological explanations for this pattern, we tested whether sampling effort might be correlated with host body size. We found that there was an almost identical negative triangular distribution of independent studies of charadriiform feather mites and host body size. Number of independent studies per host taxon was strongly positively correlated with number of mites reported from that taxon. The conflation of sampling effort with bird body mass created the strangely skewed relationship between host mass and mite richness.
