Limited consequences of infestation with a blood‐feeding ectoparasite for the nestlings of two North Pacific seabirds

Abstract

The seabird tick Ixodes uriae parasitizes over 60 host species in the circumpolar regions of both hemispheres. To assess the impacts of these ticks on the growth and development of nestling seabirds, we used a logistic growth model to interpolate between successive measures of mass (g) and wing chord (mm) for 558 Cassin's auklet Ptychoramphus aleuticus and 344 rhinoceros auklet Cerorhinca monocerata chicks over 11 years (1997–2008, less 2003) on Triangle Island, British Columbia, Canada. From the model, we estimated the asymptotic measure and the age at inflection point for each chick's growth trajectory, and assessed their relationships with tick load relative to other sources of annual and seasonal variation in growth. Most chicks (72.4% of Cassin's auklets, 62.2% of rhinoceros auklets) hosted ≥ 1 ticks, and the median tick load on infested chicks was two in both species. Infestation rates varied by a factor of about two among years (0.42 to 0.87 overall), but were uncorrelated between species and with air temperatures over the preceding winter. The probability of hosting a tick declined strongly with chick age, mainly in the first 20 days after hatching, and to near zero by fledging. Asymptotic weights and/or wing lengths declined with tick load in both species, but at normal loads the reductions were minor relative to those imposed by other factors; only at very high loads, which were rare, were effects likely to be biologically relevant. Tick load and survival to fledging were unrelated in both species. While our study found little influence of ticks, we believe there is need for further study of the relationships between parasites and seabird demography, especially in light of ongoing environmental change.

Infestation of small seabirds by Ornithodoros maritimus ticks: Effects on chick body condition, reproduction and associated infectious agents

“…Monitoring of tick infestation could be conducted to explore potential increase over time, such as that reported as a function of warmer winter temperature in an arctic population of Brünnich's guillemots (Uria lomvia) (Descamps, 2013). Prevalence of ticks infesting seabirds has been shown to be very variable among seabird species, breeding colonies and/or years ranging 0% and > 70% (Feare, 1974;Merino et al, 1999;Ramos et al, 2001;Descamps, 2013;Hipfner et al, 2019). However, the effects of ticks on hosts depend also on the tick load, the host species, the age of the host (e.g.…”

“…However, the effects of ticks on hosts depend also on the tick load, the host species, the age of the host (e.g. the effects can be different for nestlings and adults), and/or the environmental conditions, as explained above (Feare, 1974;Merino et al, 1999;Ramos et al, 2001;McCoy et al, 2002;Descamps, 2013;Hipfner et al, 2019). For example, Feare (1976) documented a 67% of tick prevalence on Sooty terns and high mortality effects, while Hipfner et al…”

“…First, anaemia caused by blood loss could be lethal for young nestlings infested by high numbers of ticks (Wanless et al, 1997). In fact, several studies have evidenced negative effects of ticks on nestlings' body condition, at least during harsh environmental conditions or high parasite loads (Morbey, 1996;Bosch and Figuerola, 1999;McCoy et al, 2002;Hipfner et al, 2019). Given their very small body size (< 10 g when hatching, Davis, 1957), storm petrel nestlings could be more susceptible to ectoparasites as ticks than larger seabird species (Merino et al, 1999).…”

“…On the other hand, non-lethal but also negative effects have been documented on seabird body condition and/or nestlings' growth rates (e.g. Bosch and Figuerola, 1999;McCoy et al, 2002;Hipfner et al, 2019). However, sometimes the effects of ticks are not evident until infestation levels are very high (Gauthier-Clerc et al, 2003;Hipfner et al, 2019) or may depend on the environmental conditions experienced by the hosts (McCoy et al, 2002).…”

“…Bosch and Figuerola, 1999;McCoy et al, 2002;Hipfner et al, 2019). However, sometimes the effects of ticks are not evident until infestation levels are very high (Gauthier-Clerc et al, 2003;Hipfner et al, 2019) or may depend on the environmental conditions experienced by the hosts (McCoy et al, 2002). Although ticks can have an important role in seabird population dynamics, specific studies on the demographic effects of tick infestation on seabirds are still scarce (Dietrich et al, 2011;Rodríguez et al, 2019).…”