A test of the nest sanitation hypothesis for the evolution of foreign egg rejection in an avian brood parasite rejecter host species

Abstract

Hosts of avian brood parasites have evolved diverse defenses to avoid the costs associated with raising brood parasite nestlings. In egg ejection, the host recognizes and removes foreign eggs laid in its nest. Nest sanitation, a behavior similar in motor pattern to egg ejection, has been proposed repeatedly as a potential pre-adaptation to egg ejection. Here, we separately placed blue 3D-printed, brown-headed cowbird (Molothrus ater) eggs known to elicit interindividual variation in ejection responses and semi-natural leaves into American robins' (Turdus migratorius) nests to test proximate predictions that (1) rejecter hosts should sanitize debris from nests more frequently and consistently than accepter hosts and (2) hosts that sanitize their nests of debris prior to the presentation of a foreign egg will be more likely to eject the foreign egg. Egg ejection responses were highly repeatable within individuals yet variable between them, but were not influenced by prior exposure to debris, nor related to sanitation tendencies as a whole, because nearly all individuals sanitized their nests. Additionally, we collected published data for eight different host species to test for a potential positive correlation between sanitation and egg ejection. We found no significant correlation between nest sanitation and egg ejection rates; however, our comparative analysis was limited to a sample size of 8, and we advise that more data from additional species are necessary to properly address interspecific tests of the pre-adaptation hypothesis. In lack of support for the nest sanitation hypothesis, our study suggests that, within individuals, foreign egg ejection is distinct from nest sanitation tendencies, and sanitation and foreign egg ejection may not correlate across species.

Self‐referent phenotype matching is a poor predictor of egg rejection by American Robins

“…The eggs were painted a deep‐blue color (ultramarine series 1; Winsor & Newtown Galeria Acrylic, Galesburg, IL, USA) in three overlapping coats. Model eggs of this size and color are known to be rejected by female robins at intermediate (30‐70%) rates (Luro and Hauber 2017, Abolins‐Abols and Hauber 2019a,b, this study) and in an individually consistent manner across repeated exposures (e.g., the same female either predominantly rejects–rejects or accepts–accepts it in subsequent trials; Croston and Hauber 2014b, Luro and Hauber 2017). Following the onset of incubation by female robins, the modal and median rejection latencies of this kind of model egg are both one day (Croston and Hauber 2014b, Abolins‐Abols and Hauber 2020a,b).…”

“…Model 3D‐printed eggs were commercially sourced (Shapeways.com, model: cow bird) and resembled Brown‐headed Cowbird eggs in shape, size, and weight (following Igic et al 2015, Luro and Hauber 2017, Hauber et al 2019b). The eggs were painted a deep‐blue color (ultramarine series 1; Winsor & Newtown Galeria Acrylic, Galesburg, IL, USA) in three overlapping coats.…”

“…This includes the individually repeatable eggshell coloration of female American Robins ( Turdus migratorius ), an occasional host of obligate brood‐parasitic Brown‐headed Cowbirds ( Molothrus ater ; Croston and Hauber 2015). American Robins have been the subject of many classic and recent parasitic egg‐rejection studies (e.g., Friedmann 1929, Rothstein 1982, Briskie et al 1992, Rasmussen et al 2009, Lang et al 2014, Abernathy and Peer 2015, Igic et al 2015, Carmody et al 2016, Luro and Hauber 2017, Luro et al 2018).…”

Which egg features predict egg rejection responses in American robins? Replicating Rothstein's (1982) study

“…For Rothstein's () data, we combined data of robins’ responses to model eggs in both the nesting (i.e., laying) and incubation stages (i.e., stages 1 and 2, respectively) because our data also came from both nesting periods unseparated. The nest stage at either the start or end of an experimental parasitism trial does not significantly influence robins’ responses to the model eggs placed in their nests at the Ithaca and Urbana study sites where our own experiments took place (Croston & Hauber, ; Luro & Hauber, ). Likewise, Rothstein () acknowledged results would have only been slightly different if data from both nesting stages were combined.…”

Cold weather events provoke egg ejection behaviour in open‐nesting passerines

“…, ). Egg ejection could also be a result of nest sanitation behaviour when birds eject their own unhatched eggs (Guigueno & Sealy , Luro & Hauber ). However, ejection of their own viable eggs by incubating female European Pied Flycatchers Ficedula hypoleuca was reported when the mean and minimum temperatures of the day before ejection were especially low (Lobato et al .…”