Vocal instability over time in individual male European nightjars,Caprimulgus europaeus: recommendations for acoustic monitoring and surveys

Abstract

Vocal instability over time in individual male European Nightjars, Caprimulgus europaeus: recommendations for acoustic monitoring and surveys.Acoustic monitoring of birds is developing rapidly as equipment, methods and analyses improve. However, most population monitoring studies still utilise traditional techniques like mark-recapture or line transects. Rebbeck et al. (2001) used vocal recordings of male European nightjars, Caprimulgus europaeus, to identify individuals, finding that four acoustic parameters correctly assigned 98.5% of calls to individuals.We tested Rebbeck et al.'s methods on a population of European nightjars recorded over two successive breeding seasons and found that percentage of males correctly classified within a season reached a maximum of 73.5%, rising to 75% if full-length calls and 13 acoustic parameters were used. We tested whether males could be reidentified over a two-year period and found that only 20% of calls were assigned to the same putative territorial individuals, despite separate ringing data showing that males can maintain site fidelity for up to eight years. Our results indicate that the characteristics of male nightjar vocalisations may alter over time. We therefore recommend that vocal discrimination be used in conjunction with existing monitoring techniques when surveying for population monitoring, that as many call parameters as possible are used and that recording for automated presence/absence surveys takes place over a short time-frame.

A comparison of the sampling effectiveness of acoustic recorder, camera trap and point count methods in sampling nocturnal birds in Afrotropical landscapes

“…Amongst the survey methods are the broadcasting method, i.e. the use of playbacks (Kemp et al, 2009), the distance census techniques (Bartolomei et al, 2013;Dayananda et al, 2016;Moreno-Mateos et al, 2011), the use of automated acoustic recorders (Docker et al, 2020;Goyette et al, 2011;Raymond et al, 2020) and other non-invasive sampling methods such as the use of molecular methods like DNA analysis from faecal and feather samples (Pedroso et al, 2018). Others involve the use of geolocators for species-specific studies (Evens et al, 2017).…”

Evaluating the potential effects of capturing and handling on subsequent observations of a migratory passerine through individual acoustic monitoring

“…In two other non-passerine species, IAM has provided understanding of the breeding season territory dynamics and movements of individuals (corncrake Crex crex: Mikkelsen et al 2013; European nightjar Caprimulgus europaeus: Rebbeck et al 2001). Recently, however, Raymond et al (2020) highlighted that in the latter species, temporal vocal instability may limit the usefulness of the IAM approach. Though use of IAM in passerines is less common, its applicability in assessing apparent survival rates and territorial behaviour has been demonstrated in species with simple (Laiolo et al 2007, Kirschel et al 2011 as well as more complex songs (Petrusková et al 2016).…”