Vocal activity of the Ferruginous pygmy-owl (Glaucidium brasilianum) is strongly correlated with moon phase and nocturnal temperature

Abstract

Bird vocal activity is affected by endogenous and exogenous factors. Owl surveys are mainly based on the detection of nocturnal calls, and therefore, the impact of exogenous factors on owls’ vocal activity may have consequences in conservation planning and behavioural studies. However, our current knowledge about the impact of climatic factors and the moon phase on owl calling behaviour is very limited, especially in the Neotropics. We used autonomous recording units to evaluate the effect of air temperature, rainfall, relative air humidity, and percent of the moon illuminated on the vocal occurrence (active/inactive) of the Ferruginous pygmy-owl (Glaucidium brasilianum) over three consecutive moon cycles in the Brazilian Pantanal. Vocal activity was positively associated with the percent of the moon illuminated, with 75% of the nights on which the species was vocally active having a moon illumination percentage higher than 77%. The vocal activity of the species was negatively associated with the nocturnal air temperature, with more vocal activity observed on cooler nights. Relative air humidity and daily rainfall were not associated with the vocal activity of the Ferruginous pygmy-owl. Our study improves the knowledge about the impact of exogenous factors on the calling behaviour of Neotropical owls. We conclude that future surveys aiming to detect the Ferruginous pygmy-owl should be carried out on nights with a high percent of moon illumination (>75%) and nights with low average temperature (< 18 °C).

KEY WORDS:

• autonomous recording unit
• bird
• Brazil
• call
• Kaleidoscope Pro
• Pantanal
• passive acoustic monitoring

HIGHLIGHTS

• Vocal behaviour of owls is affected by exogenous factors.

• We assessed the relationship between moon phase and climatic conditions with the calling activity of the Ferruginous pygmy-owl in the Pantanal.

• Calling activity was positively associated with moon phase and negatively related to nocturnal air temperature.

• Future surveys for detecting the species should be performed on nights with high percent of the moon illuminated and cooler than 18 C.

ACKNOWLEDGEMENTS

We thank the SESC Pantanal, Mato Grosso, for permission to conduct research on their property and their logistical help with our fieldwork. Prof. Dr José de Souza Nogueira and Lucas Douglas Rothmund, PhD student, from the Post-Graduate Program in Physics at the UFMT kindly provided temperature and rainfall data for our study. We thank Ana Silvia Tissiani for her technical support. This study is part of the biodiversity monitoring project Sounds of the Pantanal – The Pantanal Automated Acoustic Biodiversity Monitoring of INAU, Cuiabá, Mato Grosso, Brazil, which was conducted under SISBIO permit no. 39095 (K.-L. Schuchmann). We are grateful to two anonymous reviewers whose comments helped to improve the manuscript.

DISCLOSURE STATEMENT

The authors declare that there is no conflict of interest.

AUTHOR CONTRIBUTIONS

(1) Conceived the idea, design, experiment (supervised research, formulated question or hypothesis): C. Pérez-Granados, K.-L. Schuchmann, M.I. Marques. (2) Performed the experiments (collected data, conducted the research): K.-L. Schuchmann, M.I. Marques. (3) Wrote the paper (or substantially edited the paper): C. Pérez-Granados, K.-L. Schuchmann, M.I. Marques. (4) Developed or designed methods: C. Pérez-Granados. (5) Analyzed the data: C. Pérez-Granados. (6) Contributed substantial materials, resources, or funding: K.-L. Schuchmann, M.I. Marques.

SUPPLEMENTARY MATERIAL

Supplemental data for this article can be accessed https://doi.org/10.1080/03949370.2020.1820582.

Additional information

Funding

We greatly appreciate the financial support from the following institutions: This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior–Brasil (CAPES)-Finance Code 01; Instituto Nacional de Ciência e Tecnologia em Áreas Úmidas (INAU/UFMT/CNPq); Centro de Pesquisa do Pantanal (CPP); and Brehm Funds for International Bird Conservation (BF), Bonn, Germany.