Introduction
Bumblefoot (pododermatitis) is a necrotic inflammation of an animal's foot caused by bacterial infection (Müller et al. Reference Müller, Wernery and Kösters2000). It has been observed in various species, including rodents and rabbits (Blair Reference Blair2013). This condition is particularly prevalent among animals in poultry farms and zoos (Halliwell Reference Halliwell1975, Ekstrand et al. Reference Ekstrand, Algers and Svedberg1997, Martrenchar et al. Reference Martrenchar, Boilletot, Huonnic and Pol2002, Müller et al. Reference Müller, Wernery and Kösters2000, Wyss et al. Reference Wyss, Schumacher, Wenker, Hoby, Gobeli and Arnaud2015), and, if left untreated, it can result in permanent disability or death (Kim et al. Reference Kim, Parlk, Hong, Jung and Kim2022). Bumblefoot has been documented in captive penguins, swans and flamingos (Reidarson et al. Reference Reidarson, McBain and Burch1999, Kim et al. Reference Kim, Parlk, Hong, Jung and Kim2022). However, bumblefoot has not been reported in free-ranging birds (Herman et al. Reference Herman, Locke and Clark1962, Wyss et al. Reference Wyss, Schumacher, Wenker, Hoby, Gobeli and Arnaud2015), except for in birds of prey (Stoner & Stoner Reference Stoner and Stoner1945, Cooper Reference Cooper1973). In addition, bumblefoot has most often been observed in adult birds, except for one mild histological lesion in a flamingo chick (Wyss et al. Reference Wyss, Schumacher, Wenker, Hoby, Gobeli and Arnaud2015).
Bumblefoot is caused by various factors, such as an animal's weight, the material and composition of flooring and nutritional status (Reidarson et al. Reference Reidarson, McBain and Burch1999, Martrenchar et al. Reference Martrenchar, Boilletot, Huonnic and Pol2002, Nauaraj et al. Reference Nauaraj, Bilgili, Hess and Biguzzi2006). According to Choi et al. (Reference Choi, Buhl and Ponder2016), the symptoms of bumblefoot can be categorized into seven grades. Grade I symptoms include some flaking of the pad surface with a pink and shiny area. In Grade II, the soles are worn and red, but no distinct ulcers are present. Starting in Grade III, the pads swell and ulcers (or calluses) develop. In advanced stages, ulceration may spread from the footpad to the tendons and bone marrow (Choi et al. Reference Choi, Buhl and Ponder2016, Rasidi Reference Rasidi2020). The treatment of bumblefoot requires removal of the cause of the disease and additional surgical treatment. If untreated or inadequately treated, bumblefoot can eventually lead to death (Cooper Reference Cooper1973, Schneider et al. Reference Schneider, Hunter, Waltner-Toews and Barker1988, Kim et al. Reference Kim, Parlk, Hong, Jung and Kim2022).
This paper reports the first observation of bumblefoot in south polar skua (Stercorarius maccormicki) chicks.
Observation
Chick monitoring of the south polar skua was carried out at three sites on the northern Victoria Land coast, Antarctica: Cape Hallett (72°19'S, 170°12′E), Cape Möbius (74°38′S, 164°13′E) and Inexpressible Island (74°55′S, 163°43′E) from mid-January to early February in both 2022 and 2023 (Supplemental Material). The breeding sites have ~140, 100 and 50 breeding pairs of south polar skuas, respectively. The ground components of the three breeding sites are different: Inexpressible Island consists only of boulders, Cape Möbius consists of large rocks and some sand and Cape Hallett consists of gravel. The chicks of south polar skuas were ~20–30 days old at the time of the monitoring, and they able to walk around their nests.
On 2 February 2022, we observed ulcers and enlargement on the footpads of two south polar skua chicks on Inexpressible Island (Fig. 1). Based on localized pad enlargement and the presence of ulcers, we diagnosed these cases as grade III bumblefoot. Notably, ulcers on the foot were not detected in any other skua chicks during the same breeding seasons. In the 2023 monitoring period, we observed flaking on the soles of some chicks (40 out of 76) across the three breeding sites, leading to suspicions of grade I or II bumblefoot.
Figure 1. Bumblefoot in the south polar skua chicks on Inexpressible Island. The ulcers on the foot are indicated by the red circles.
Although overt bumblefoot, a symptom of grade III or higher (Choi et al. Reference Choi, Buhl and Ponder2016, Rasidi Reference Rasidi2020), was confirmed in only two chicks during the 2022 breeding season (Fig. 1), early signs of bumblefoot were suspected in many individuals. Bumblefoot is probably induced in skua chicks by them having a heavy weight before fledging (Schmidt & Lightfoot Reference Schmidt and Lightfoot2006), the roaming walk of chicks (Young Reference Young1963) and flooring substrates (Reidarson et al. Reference Reidarson, McBain and Burch1999). Specifically, on Inexpressible Island, where rough rocks cover much of the surface, skua chicks probably developed sores on the contact surface of their foot pads, as their weight would have been concentrated on only a small portion of the pad (Hawkey et al. Reference Hawkey, Samour, Henderson and Hart1985, Reidarson et al. Reference Reidarson, McBain and Burch1999, Reisfeld et al. Reference Reisfeld, Barbirato, Ippolito, Cardoso, Nichi, Sgai and Pizzutto2013). Therefore, this study suggests that bumblefoot may develop in the chicks of other Charadriiformes species that breed on rocky terrain. Furthermore, bacterial sampling of the affected areas needs to be performed in the future for accurate diagnosis.
This study has revealed the presence of bumblefoot in south polar skua chicks. This is the first case of bumblefoot in a free-ranging bird that is not a bird of prey. This report suggests that bumblefoot needs to be considered in terms of the health of birds breeding in rocky areas. These findings highlight the importance of continuing research to understand the impacts of bumblefoot on wild birds.
Acknowledgements
We thank Myeongho Seo and Doyun Lee for their help in the field, Kyungho Lee for the English editing, the overwintering members for logistical support at Jang Bogo Station and the editor and reviewers for improving the manuscript.
Financial support
This work was supported by ‘Study on polar ecosystem change by warming and adaptation mechanisms of polar organism’ funded by Korea Polar Research Institute (PE24140) and ‘Ecological Monitoring of Antarctic Specially Protected Areas and Environmental Management Around Antarctic Stations’ funded by the Korean Ministry of Environment (PG24040).
Author contributions
KYM: conceptualization, investigation, writing - original draft, writing - review and editing. JUK and YGO: investigation, writing - review and editing. JHK: conceptualization, writing - review and editing, supervision, funding acquisition.
Supplemental material
A supplemental table and supplemental data file will be found at https://doi.org/10.1017/S0954102024000452.
Open access
