Solitary breeding barn swallows pay a higher nest defense cost
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Solitary breeding barn swallows pay a higher nest defense cost Javier Balbontín1 · Luis López‑Sígler1 · Roberto Muriel2 · Cosme López‑Calderón1 Received: 27 November 2019 / Accepted: 2 June 2020 © Japan Ethological Society 2020
Abstract Successful reproduction depends on the ability of parents to defend from nest predators. Breeding birds often put their life at risk to defend their offspring from predators. Communal nest defense has been proposed as an individual benefit of group living. We tested this by experimentally exposing a short-lived avian species to a potential risk of predation. We presented decoys of both a diurnal and a nocturnal predator to barn swallows Hirundo rustica breeding solitarily and in large colonies in South-western Spain. We found clear benefits of group living compared to solitary pairs in relation to investment in individual nest defense and the capacity to deter a challenging predator. Although we did not find differences in the time needed to detect the predator, we found that the number of individuals recruited to participate in nest defense was greater for colonial breeding pairs, leading to fewer attacks per individual in comparison to solitary breeding pairs. We also found that barn swallows defended their nests more vigorously against a nocturnal predator than against a diurnal predator. Therefore, barn swallows living in groups obtained clear benefits in communal nest defense by reducing the risk, energy and time dedicated to nest defense. Colonial breeding is thus a more effective strategy for decreasing nest predation rates. Keywords Barn swallow · Coloniality · Hirundo rustica · Mobbing · Parental investment · Predation risk · Life history
Introduction Breeding in groups forming colonies is a common behaviour in vertebrates and invertebrates (Maynard Smith and Szathmary 1997). The level of association can vary extensively from breeding in isolation to breeding in close or packed colonies with many intermediate forms being likely states throughout the animal kingdom (Brown and Brown 1996). Benefits of coloniality include increased foraging efficiency by information-sharing between individuals on the location of dispersed food patches (Brown and Brown 1996; Rolland et al. 1998) and reduction in nest predation through increased levels of nest vigilance or communal nest defense (Kruuk 1964; Anderson et al. 1980; Hoogland and Sherman 1976; Wiklund and Andersson 1994; Kontiainen et al. 2009). Conversely, costs associated with group living include higher parasitisation risk and increased competition * Javier Balbontín [email protected] 1
Departamento de Zoología, Facultad de Biología, Edificio Verde, Avda. de Reina Mercedes s/n, 41012 Sevilla, Spain
Applied Ecology Group, Estación Biológica de Doñana (CSIC), c/ Americo Vespucio 26, 41092 Sevilla, Spain
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for resources or mates that usually result in reduced fitness (Rekásí et al. 1997; Sachs et al. 2007). Organisms allocate resources to maximise lifetime reproductive success (Williams 1966; Charnov and Krebs 1
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