Knowledge of vocal behaviours can provide important insights about populations that may have conservation problems; indeed, these behaviours give us a big amount of information about the environments in which the organisms live and any recent habitat changes, as well as valuable information about the health status of the individuals themselves.
By monitoring vocal behaviour, we can derive demographic parameters that are relevant to conservation such as reproductive success and mortality rates; through vocalisations, which act as alarm systems, we can predict the possible decline or potential growth of a population.
Some types of vocalisations may provide direct measures of recruitment
If vocalisations accompany parturition or hatching, success rates could be estimated by monitoring them; or, in some species, they may signal the presence of cubs, nestlings or juveniles through different vocal repertoires or through the analysis of frequencies, calls rates, entropy and sound pressure levels at the source.
In addition, vocalisations related to food and provisioning – in many ornithic species known as begging – could provide information on the availability of trophic resources in the environment and constitute direct measures of feeding. At the same time, these types of calls may give details about the personality and characteristics of individuals: high-quality chicks can produce high call rate to facilitate allofeeding by parents to the strongest; conversely, chicks may vocalise more intensely to signal a true need and parents will feed the weakest offspring.
In a bioacoustic monitoring program, the specific acoustic signals to be monitored will clearly vary depending on the target species and research question. However, before starting a bioacoustic monitoring program, it is of paramount importance that the vocal repertoire and behaviour are known. Unfortunately, for many large birds such as diurnal raptors or waterbirds, there are few studies on these issues.
A bioacoustic approach is needed to deepen our knowledge of the meaning of sounds emitted and to discover when and why calls and/or songs are produced, paying particular attention to the interactions between individuals during the breeding and parental care periods. Other behavioural contexts must be considered, such as interspecific competition and predation.