Reed Warbler Hosts Do Not Fine-Tune Mobbing Defenses During the Breeding Season, Even When Cuckoos Are Rare

Hosts of brood parasitic cuckoos often employ mobbing attacks to defend their nests and, when is costly, hosts are predicted adjust match parasitism risk. While evidence exists for fine-tuned plasticity, it remains unclear why does not track larger seasonal changes in Here we test a possible explanation from parental investment theory: parents should current more intensively as the opportunity replace declines (re-nesting potential), and therefore “counteract” any apparent decline We take advantage experiments conducted at two sites where reed warblers ( Acrocephalus scirpaceus ) experience (in Italy), or do Finland), parasitism. that be higher overall Italy, but remain constant over season other parasitised sites, whereas Finland pose local threat, low beginning increase re-nesting potential declined. However, while were likely mobbed found little changed either parasitized non-parasitized sites. This suggests has influence on behavior, its effects obscured by differences ecology hosts.