Nest desertion cannot be considered an egg‐rejection mechanism in a medium‐sized host: an experimental study with the common blackbirdTurdus merula

Abstract

Two main mechanisms of egg rejection, the main defence of hosts against brood parasites, have been described: ejection and desertion. Desertion of the parasitized nest is much more costly and is usually exhibited by small-sized host species unable to remove the parasitic egg. However, nest desertion is frequently assumed to be an anti-parasite strategy even in medium or large-sized host species. Th is assumption should be considered with caution because: 1) large-sized hosts able to eject the parasitic egg should eject it rather than desert the nest, and 2) breeding birds may desert their nests in response to diff erent disturbances other than brood parasitism. Th is problem is especially important in the common blackbird Turdus merula because this is a medium-sized species, potential host of the common cuckoo Cuculus canorus , in which desertion has been frequently reported as a response to cuckoo egg models. Here, we seek to determine whether nest desertion can be considered a response unequivocally directed to the parasitic egg in medium-sized hosts using the blackbird as the study species. In an experimental study in which we have manipulated levels of mimicry and size of experimental eggs, we have found that both colour (mimetic and non-mimetic; at least for human vision) and size (small, medium, and large) signifi cantly aff ected ejection rates but not nest desertion rates. In fact, although large eggs disproportionally provoked nest desertion more frequently than did small or medium-sized eggs, cuckoo-sized parasitic eggs were not deserted allowing us to conclude that desertion is unlikely to be an adaptive response to brood parasitism at least for this species.

Size and material of model parasitic eggs affect the rejection response of Western Bonelli's Warbler Phylloscopus bonelli

“…, Soler et al . ). We considered the model egg to have been accepted when it remained warm in the nest for 5 days, even if it had marks left by the bill (one case).…”

“…Soler et al . () found that in Common Blackbirds Turdus merula , a medium‐sized host considered to be a grasp ejector (Davies & Brooke , Honza et al . , Soler et al .…”

Daurian redstart Phoenicurus auroreus is a host for the common cuckoo Cuculus canorus during the second, but not the first cultch

“…However, some medium-and large-sized hosts such as grey-backed thrushes (Turdus hortulorum), blackbirds (Turdus merula), and common grackles (Quiscalus quiscula) do not desert parasitized nests instead of ejecting parasitic eggs [35][36][37]. Moreover, nest desertion can be triggered by other factors such as parental mortality, human disturbance, or egg loss [38][39][40].…”

Peer Review #1 of "Using 3D printed eggs to examine the egg-rejection behaviour of wild birds (v0.1)"

“…It allows precise manipulation of egg shape and potentially, shell thickness, making it potentially possible to create egg shapes that can, or cannot, be grasped and removed from the nest (Rohwer & Spaw 1988) or eggs with shells that are thin enough, or too thick, for hosts to reject by puncturing the shell (Antonov et al 2006a;Spottiswoode 2010). Indeed, when artificial eggs cannot be pierced by small hosts, rejection of eggs by piercing their shells may not be possible, and thereby generate spurious results of egg acceptance or nest abandonment, instead of egg ejection (Martín-Vivaldi, Soler & Møller 2002;Boulton & Cassey 2006;Soler et al 2015). However, the capacity for 3D printing to produce artificial eggs that can be rejected by hosts via puncturing their shells may be possible in the future, with the advent of light and brittle printable materials; this concept PeerJ reviewing PDF | (2015:03:4467:1:0:NEW 27 Apr 2015)…”

“…Robins generally reject eggs within five days following parasitism (Croston & Hauber 2014) by grasping them in their bills and carrying them away from the nest (Video S1; Rothstein 1975;Rasmussen, Sealy & Underwood 2009). By using a large grasp-ejector species in our experiments, such as the American robin, we avoided potential spurious results of egg acceptance because artificial eggs cannot be pierced (Martín-Vivaldi, Soler & Møller 2002;Boulton & Cassey 2006;Soler et al 2015) and isolated rejection probabilities to the recognition of parasitic eggs by hosts (Hauber & Low 2014;Mendelson 2015), rather than physical constraints of rejecting eggs of particular size or shape. Indeed, our specific aim was to examine how egg size and shape influence robins' egg rejection decisions, rather than the physical constraints on egg rejection.…”