Distress calls reflect poxvirus infection in lesser short-toed lark Calandrella rufescens

Several studies have highlighted the association between birdsong and parasite load, but there is no evidence regarding therelationships among pathogens and alarm or distress calls, whichare used in antipredator strategies. We analyzed the associationbetween virus infection and the distress calls of lesser short-toedlark (Calandrella rufescens), addressing the relationships betweencall acoustic properties, presence of poxvirus lesions, andother measurements of bird health (body condition, T-cell–mediatedimmune response, heterophils-to-lymphocytes ratio H/L ratio],and blood parasites). The study was carried out in Fuerteventura(Canary Islands), where 55% of lesser short-toed larks wereinfected. Pox infection was associated with changes in the spectrotemporalstructure of lark distress calls and affected the condition-dependentnature of these signals. Virus bearers uttered significantlyshorter and lower pitched calls than virus-free birds, givingeven shorter calls when subject to greater physiological stress(higher H/L ratio), whereas virus-free individuals did the opposite.Call harshness was positively correlated with bird immune andbody condition, independently of virus infection, whereas callpulse rate decreased in stressed birds. We hypothesize thathealthy birds might reveal their ability to bear the costs ofantipredator defense by means of long, harsh, and fast modulateddistress calls. Infection not only affects individual stateand morphology by means of gross lesions but also may altera signal used in an antipredator context, thus potentially reducingbird fitness both directly (through disease) and indirectly(through increased predation).