Mast seeding causes strong fluctuations in populations of forest animals. Thus, this phenomenon can be used as a natural experiment to examine how variation in host abundance affects parasite loads. We investigated fleas infesting yellow‐necked mice in beech forest after 2 mast and 2 non‐mast years. We tested 2 mutually exclusive scenarios: (1) as predicted by classical models of density‐dependent transmission, an increase in host density will cause an increase in ectoparasite abundance (defined as the number of parasites per host), versus (2) an increase in host density will cause a decline in flea abundance (“dilution,” which is thought to occur when parasite population growth is slower than that of the host). In addition, we assessed whether masting alters the relationship between host traits (sex and body mass) and flea abundance. We found a hump‐shaped relationship between host and flea abundance. Thus, the most basic predictions are too simple to describe ectoparasite dynamics in this system. In addition, masting modified seasonal dynamics of flea abundance, but did not affect the relationship between host traits and flea abundance (individuals with the highest body mass hosted the most fleas; after controlling for body mass, parasite abundance did not vary between sexes). Our results demonstrate that pulses of tree reproduction can indirectly, through changes in host densities, drive patterns of ectoparasite infestation.

Basking in the sun is an important energy‐saving tactic in ectotherm animals. It has also been recognized to be important in several mammal species, especially in arid environments. In particular, small mammals that have a greater surface‐to‐volume ratio can use basking to reduce metabolic energy expenditure by using external heat to maintain a high body temperature. If basking mainly functions to passively gain heat, animals should choose basking spots that offer a more favorable micro‐climate for warming up. We tested this hypothesis in African striped mice (Rhabdomys pumilio), a diurnal species that is known to bask. Over 19 months, we displaced 138 individuals from their basking spots and immediately thereafter measured the temperature of the surface (Ts) at these spots. We expected that striped mice choose spots for basking that are warmer than random spots, especially in (1) the morning, when Ts is lower compared to afternoon, and (2) the dry season characterized by low food availability in which energy gain due to basking is more beneficial than in the moist season with high food availability. Moreover, we tested whether there are differences in relative safety (measured as available plant cover) at basking spots compared to random spots. Temperature of the surface (Ts) was significantly higher at basking spots than at random spots. However, we did not find any differences in ΔT in relation to season, time of the day or in the safety between basking and random spots. In conclusion, our study indicates that striped mice choose basking spots with a favourable microclimate characterized by higher surface temperature.

We investigated the presence and potential causes of sex bias in ectoparasite infestations in the yellow-necked mouse Apodemus flavicollis. We compared the natural tick and flea burdens of male and female mice in a temperate beech forest and assessed whether the observed differences were driven by host sex or body mass. We found that males were more heavily infested by ticks compared to female mice. However, this difference was driven by host body mass, and not sex itself. Host body mass positively correlated with flea loads, but there was no evidence of sex bias in flea abundance. In addition, the abundance of both ticks and fleas infesting yellow-necked mice changed over time, both seasonally (month to month) and annually (year to year). Our results underscore the importance of the sexual size dimorphism and the parasite taxon as the primary factors that influence the occurrence of sex-biased parasitism in small mammals.