Colony‐nesting gulls restrict activity levels of a native top carnivore during the breeding season

Abstract

Although nesting in colonies can offer substantial reproductive benefits for many seabird species, increased visibility to predators remains a significant disadvantage for most colony‐breeders. To counteract this, some seabird species have evolved aggressive nest defense strategies to protect vulnerable eggs and chicks. Here, we used an experimental approach to test whether colony inhabitance by breeding gulls Larus spp. in western Norway impacts visitation rates of a native, mammalian predator, the Eurasian otter Lutra lutra during the breeding season. Camera traps were placed inside of and on the periphery of seabird colonies prior to the breeding season and left to run for one continuous year. Sighting frequency of otters on these cameras was compared to a control region free of gull nesting. We found that otter activity was significantly reduced in the colonies when gulls were incubating and rearing chicks, compared to time periods when gulls were building nests and absent from the colonies. Rhythmic activity patterns did not seem to be significantly impacted by the presence of gulls. This study provides clear evidence that certain colony‐nesting species can have a direct, negative impact on visitation rates of a native carnivore. Seasonal carnivore activity patterns are likely to be highly dependent on differing nesting strategies and level of nest defense by seabirds.

Interspecific relationships in a suboptimal habitat, an unexpected ally for the survival of the threatened Tenerife speckled lizard (Gallotia intermedia)

“…Although the probability of attack was randomly distributed withing the colony, the frequency of attacks was strongly correlated with the abundance of the seagull’s chicks. Similar mobbing behaviours have been recorded in other seabirds’ colonies (Clode et al, 2000; Larsen, 1991), and in some cases it has been reported that other species use this indirect protection on their advantage (Gameiro et al, 2022; Guidos et al, 2023). For example, Monk parakeets ( Myiopsitta monachus ), an IAS built their nest under those of white storks ( Ciconia ciconia ) to reduce predation risk which indirectly offers protection against predators (Hernández-Brito et al, 2020).…”

“…These same ravines and platforms are used by L. michahellis colony for breeding and resting. The yellow-legged gull, as many other bird species, present an aggressive anti-predator behaviour specially during the breeding season (Clode et al, 2000; Frixione & Salvadeo, 2021; Gameiro et al, 2022; Guidos et al, 2023). Previous studies showed how seabird breeding colonies, due to its aggressive response to predators, work as facilitators for breeding of less aggressive and/or solitary species (Erwin, 1988; Gameiro et al, 2022; Quinn & Ueta, 2008; D. S. Richardson & Bolen, 1999).…”

“…These same ravines and platforms are used by L. michahellis colony for breeding and resting. The yellow-legged gull, like many other bird species, presents an aggressive anti-predator behaviour especially during the breeding season (Clode et al, 2000;Frixione & Salvadeo, 2021;Gameiro et al, 2022;Guidos et al, 2023).…”