Consistent dear enemy effect despite variation in territorial centrality and population density in Rufous Horneros

ABSTRACT

Social discrimination is used as a territorial cost-mitigation behaviour across several taxonomic groups. However, whether this phenomenon is similar across populations or varies due to local ecological traits remains an open field. Here, we tested whether social discrimination ability exhibited by pairs of Rufous Horneros (Furnarius rufus) varies between two spatially distinct Brazilian populations (Brasília and Juiz de Fora), with contrasting population densities. We predicted that Rufous Horneros would show the highest aggression towards strangers’ duets in the low-density population (the ‘dear enemy effect’), and towards neighbours’ duets in the high-density population (the ‘nasty neighbour effect’). We also examined the impact of territorial centrality (distance to the centre of the conspecific neighbourhood) on territorial responses, assuming that territorial harassment varies with centrality. We observed a consistent dear enemy effect expression (i.e. lower response to simulated intrusions by neighbours compared to strangers) across both populations, despite their differing densities. Additionally, we found no effect of territorial centrality on playback responses. Our findings show that the dear enemy effect is widely distributed in Rufous Horneros, at least in the breeding season, being observed even in a high-density population. Our findings also highlight the lack of advantages for central territories. Future studies should investigate whether territorial mitigation strategies exhibit consistency across different contexts and taxa.

KEYWORDS:

• Dear enemy effect
• territorialism
• social behaviour
• suboscines
• Furnariidae

Acknowledgments

We thank the Instituto Chico Mendes de Conservação da Biodiversidade (ICMBio) and Centro Nacional de Pesquisa e Conservação de Aves Silvestres (CEMAVE) for capturing and banding permits, and the local ethics and animal care committee (CEUA-UFJF) for approving the method procedures. We thank to the many volunteers who assisted with fieldwork in both sites, namely Fábio Palácio, Daniel Oliveira, Mariana Oliveira, Polônia Nunes, Lucas Morgado, Juliana Oliveira, Paula Neto, and Clarissa Vidal from Juiz de Fora site, as well as Eduarda Amorim, André Elias, Amada Brito, Yuri Couceiro, Henrique Paiva, Diogo Brandão, Pietra Guimarães, Renato Oliveira, and many other volunteers from Brasília site.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

Data and codes that support the findings of this study are fully available on Mendeley Data through the link: https://dx.doi.org/10.17632/7jf46k3n52.1.

Ethics statement

No birds were injured during capturing, banding, or playback experiments and field observations. In both populations, each pair was exposed to a single song per trial, ensuring a minimum interval of 24 h between trials. The birds usually resumed their normal activities within minutes after each playback procedure. All field procedures strictly adhered to the guidelines set by the local ethics and animal care committee (CEUA-UFJF) and the Brazilian environmental agencies (SISBio and CEMAVE).

Supplementary material

Supplemental data for this article can be accessed at https://doi.org/10.1080/01584197.2024.2362984

Additional information

Funding

This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) – Finance Code 001 (PhD scholarship to PSA, postdoctoral fellowship to PD under grant number 88887.469218/2019-00), the Animal Behavior Society (ABS Student Research Grant to PSA) and the Association of Field Ornithologists (E. Alexander Bergstrom Memorial Research Award to PSA).