INTRODUCTION
The interactions between birds and insects have been the subject of
extensive research (Morse, 1971; Willis & Oniki, 1978). Bird-insect
interactions in the form of predation, parasitism, and mutualism have
received the most attention because of their ubiquitous occurrence and
importance as study systems for understanding coevolution (Holmes et
al., 1979; Maziarz et al., 2021; Price, 1997; Quinn & Ueta, 2008).
Other less conventional or more cryptic interaction types also occur
along the antagonism-commensalism gradient, such as competition (e.g.
for food resources; Smith & Balda, 1979) or ‘anting’ (i.e. the use of
ants as a treatment against parasites; Camacho & Potti, 2018), but they
often go undetected or underreported and their true nature and
biological significance remain to be elucidated in most cases.
Of all insects, ants (Formicidae) are the most abundant in most
terrestrial ecosystems (Del Toro et al., 2012). There is ample
literature documenting antagonistic ant-bird interactions, primarily in
the form of bird predation on ants (reviewed in Avilés, 2023). There are
also studies reporting negative effects of ants on aspects such as bird
abundance, behaviour, and reproduction, primarily through predation on
eggs and chicks (Alvarez-Blanco et al., 2020; Davis et al., 2008;
Haemig, 1999). However, assessing the impact of ants on more mobile
segments of a population (e.g. juveniles and adults) is challenging and
our understanding of the nature and magnitude of these effects is
therefore limited.
This study takes advantage of a long-term capture-recapture program to
examine the nature and frequency of injuries (toe amputations) of a
migratory insectivorous bird –the red-necked nightjar
(Caprimulgus ruficollis )– in their breeding area in S Spain. The
study was motivated by observations of nightjars missing toes and
particularly of an adult bird recorded in 2015 that had what appeared to
be the mandible of an ant embedded in the medial toe of one of their
feet. Six years later, in 2021, we found another adult that had the full
head of an ant embedded in a central toe. Since then, we engaged in a
systematic revision of the feet of all captured nightjars to evaluate
the frequency and severity of toe injuries. Observations of insect
remains attached to injured toes in three nightjars provided an
opportunity to identify the agents of damage based on a taxonomic
analysis. We close by discussing the incidence of such injuries on
nightjar populations and identify further research needs.