Spotlight: Lice, shorebird hitch-hikers

Lice.

Probably not the first thing that comes to mind when thinking about shorebirds.

Yet, avian parasites – like hitch-hiking lice – can play a major role in shorebird life. Their effects can range from mere annoyance to a selective force strong enough to impact the behaviour, ecology, life history and perhaps even migration strategies of their hosts^1,2. Though these parasites have been studied for some time, we’ve barely scratched the surface in terms of understanding which species of louse live on which species of shorebird and how these patterns might vary geographically. Thus, much of the work to be done involves simply describing what is there.

Two studies published in this issue of Wader Study endeavour to do just that. Gustafsson and colleagues from China redescribe two species of chewing lice collected from seven Grey-headed Lapwings Vanellus cinereus caught in Jinshanyakou, China³. Tavera and colleagues from Canada and Perú delve into the occurrence and diversity of chewing lice on shorebirds in Paracas, Perú⁴.

For many people, just thinking about lice makes their heads itch. For shorebirds, chewing lice Phthiraptera live in the feathers rather than the hair, but like human head lice, they are obligate ectoparasites. They have no wings and they use biting (not sucking) mouthparts to feed on feathers, blood and dead skin. In order to live, they must hitch a ride with a bird.

Anyone who has ever done a louse check on a child (or themselves) knows that lice are not always easy to see and definitely not easy to remove. So how did the researchers go about studying bird lice?

The first step was catching the birds. In both studies, the researchers used mist nets at night. Gustafsson and colleagues set their nets up in a mountain range in September 2018 at Jinshanyakou in China.

On the other side of the world, and at sea level, Tavera and colleagues set up mist nets on the Pacific coast at the Paracas National Reserve, Perú. They caught birds in September 2017, January 2018 and March 2018 – across seasons – because they wanted to document seasonal patterns of louse abundance.

The second step was finding and then capturing the lice. In both studies, louse checks were performed immediately after the birds were caught. This is because lice can escape. Some of us have held birds and had their lice crawl right onto us. Of course, finding the lice isn’t always that easy. One way to get to them is to gas them out. Gustafsson and colleagues started with this approach. They placed the birds in bags (with their heads safely uncovered) and fumigated the feathers with ethyl acetate. This got some of the lice, but some remained hidden in the thick plumage. So, the researchers also manually searched for lice on the wings, back, rump, flanks, neck and head, using forceps to lift the feathers. Tavera and colleagues used only manual searching. They also ensured that the same observer examined body and flight feathers from all birds for a set time of 2–3 min. This minimized variation in sampling effort and technique. Once removed from the birds, the lice were stored in ethanol to be taken to the lab.

The final step was identifying what species of louse had been found. In both studies, the researchers first had to prepare the specimens. They used 20% potassium hydroxide (KOH), which softens, digests and clears the tissues, making identification easier. Then they dehydrated the specimens using increasingly stronger solutions of ethanol. Finally, they mounted each specimen on a slide and let it dry further. Only then could the researchers truly examine specimens under a light microscope and use taxonomic keys to identify the lice based on morphology.

Using these careful methods, Gustafsson and colleagues sampled a total of seven Grey-headed Lapwings. Of these, four birds were parasitized by Actornithophilus hoplopteri (nine males, ten females, eight nymphs), and one bird was parasitized by Quadraceps sinensis (six males, three females). The only bird parasitized by Q. sinensis was also parasitized by A. hoplopteri. The samples size is small because the lapwings were caught as part of a larger study on chewing lice in a number of non-shorebird species⁵. However, only a small sample was needed to achieve the authors’ goal to comprehensively redescribe both the males and females of the two species found. This will provide shorebird researchers with better identification tools to study bird lice in the future.

Tavera and colleagues caught and sampled 108 individuals of seven shorebird species and collected 160 individual lice. The lice were of the Menoponidae and Philopteridae families and the authors were further able to classify them into four genera and nine species. All of the species reported were new geographical records for shorebirds in Perú.

Tavera and colleagues found that lice were most prevalent on Ruddy Turnstones Arenaria interpres and Sanderlings Calidris alba, with 80% of birds parasitized. Western Sandpipers C. mauri were the least parasitized species, with 36% parasitized. Sanderlings hosted the highest abundance of lice, while Semipalmated Sandpipers C. pusilla had the highest species richness hosting four different species of louse.

The authors were interested in whether louse infestations negatively affected body condition, but they found no significant relationship between body condition and total parasites. Infested (or more infested) birds did not seem to have decreased body condition. So just how important are chewing lice in Perú? This study suggests that they may be a mere annoyance at the levels of infestation found.

In terms of seasonality, Tavera and colleagues saw a decreasing trend of parasite number per individual through the nonbreeding season. Although not statistically significant, the trend might indicate that individuals are losing ectoparasites during their stay at Paracas. But why? The authors speculated that the apparent decrease might indicate that habitat in Perú is ‘cleaner’ than the birds’ more northerly stopovers. This would be consistent with the hypothesis that long distance migrating shorebirds might have lower immunocompetence and thus need to use lower parasite marine habitats whenever possible². However, the apparent reduction of ectoparasite numbers could also indicate that more parasitized birds are leaving the population by emigration or death. A third explanation could be seasonality of the adult versus egg/larval life stages in the lice. Finally, body molt could be a potential reason for reducing a load of ectoparasites, especially in cases where the molt began at arrival to the non-breeding areas.

These two papers contribute to a growing body of knowledge about ectoparasites and their occurrence and effects on birds. Not everyone finds this fascinating, but we need only to look to studies of our own parasites to see the potential⁶. Humans have been infested by lice for millions of years. Like in birds, human louse infestations can mean everything from annoyance to death. Human body lice can transmit at least three intracellular pathogenic bacteria causing epidemic typhus, relapsing fever, and trench fever. They also have a global distribution – probably because they hitched rides with us as we colonized the globe – and so they can be good markers for studying human evolution.

Lice. Maybe more interesting than you might have thought.

PDF is available for download here: https://www.waderstudygroup.org/article/13213/

¹Hicks, O., S.J. Burthe, F. Daunt, M. Newell, A. Butler, M. Ito, K. Sato & J.A. Green. 2018. The energetic cost of parasitism in a wild population. Proceedings of the Royal Society B 285: 20180489.

²Piersma, T. 1997. Do global patterns of habitat use and migration strategies co-evolve with relative investments in immunocompetence due to spatial variation in parasite

pressure? Oikos 80: 623–631.

³Gustafsson, D.R., L. Lujia, C. Xingzhi, Z. Xuebing & Z. Zou. 2019. Chewing lice (Phthiraptera) of the Grey-headed Lapwing, Vanellus cinereus, in China. Wader Study 126: 217-227.

⁴Tavera, E.A., D. Minaya, E. Ortiz Lopez, J. Iannacone & D.B. Lank. 2019. Chewing lice richness and occurrence in non-breeding shorebirds in Paracas, Perú. Wader Study 126: 190–199.

⁵Gustafsson, D.R., L. Lei, K. Luo, X. Chu, X. Zhao, Q. Zhang & F. Zou. 2019. Chewing lice from high-altitude and migrating birds in Yunnan, China, with descriptions of two new species of Guimaraesiella. Medical & Veterinary Entomology 33: 407–419.