Visual acuity and egg spatial chromatic contrast predict egg rejection behavior of American robins

Abstract

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Summary StatementWe used 3D-printed model eggs with checkered patterns of varying dimensions to test how chromatic visual acuity affects egg recognition in an avian brood parasite host species, the American robin. AbstractColor and spatial vision are critical for recognition and discrimination tasks affecting fitness, including finding food and mates and recognizing offspring. For example, as a counter defense to avoid the cost of raising the unrelated offspring of obligate interspecific avian brood parasites, many host species routinely view, recognize, and remove the foreign egg(s) from their nests. Recent research has shown that host species visually attend to both chromatic and spatial pattern features of eggs; yet how hosts simultaneously integrate these features together when recognizing eggs remains an open question. Here, we tested egg rejection responses of American robins (Turdus migratorius) using a range of 3D-printed model eggs covered with blue and yellow checkered patterns differing in relative square sizes. We predicted that robins would reject a model egg if they could visually resolve the blue and yellow squares as separate features or accept it if the squares blended together and appeared similar in color to the natural blue-green color of robin eggs as perceived by the avian visual system. As predicted, the probability of robins rejecting a model egg increased with greater sizes of its blue and yellow squares. Our results suggest that chromatic visual acuity and viewing distance have the potential to limit the ability of a bird to recognize a foreign egg in its nest, thus providing a limitation to host egg recognition that obligate interspecific avian brood parasites may exploit. 409 410 411 412 413 414 Abolins-Abols, M., Hanley, D., Moskát, C., Grim, T. and Hauber, M. E. (2019). Antiparasitic egg rejection by great reed warblers (Acrocephalus arundinaceus) tracks differences along an eggshell color gradient. Stokke, B. G. (2010). Avian colour perception predicts behavioural responses to experimental brood parasitism in chaffinches. J. Evol. Biol. 23, 293-301. Bürkner, P. C. (2017). brms: An R package for Bayesian multilevel models using Stan. J. Stat. Softw. 80, 1-28. Canniff, L., Dainson, M., López, A. V., Hauber, M. E., Grim, T., Samaš, P. and Hanley, D. (2018). Probing the limits of egg recognition using egg rejection experiments along phenotypic gradients. J. Vis. Exp. 2018, e57512. Cassey, P., Honza, M., Grim, T. and Hauber, M. E. (2008). The modelling of avian visual perception predicts behavioural rejection responses to foreign egg colours. Biol. Lett. 4, 515-517. Caves, E. M. and Johnsen, S. (2017). AcuityView: An r package for portraying the effects of visual acuity on scenes observed by an animal. Methods Ecol. Evol. 9, 793-797. Princeton University Press. Croston, R. and Hauber, M. E. (2014). Spectral tuning and perceptual differences do not explain the rejection of brood parasitic eggs by American robins (Turdus migratorius). Behav. Ecol. Sociob...

The American robin (Turdus migratorius): A focal species for anti‐parasitic egg rejection studies among hosts of the brown‐headed cowbird (Molothrus ater)

“…Egg maculation color and patterning, combined with egg background coloration are multicomponent visual cues that birds may use when viewing and recognizing foreign eggs in their nests (Hanley et al., 2019). Accordingly, in a recent experimental study where robins were presented with checkered model eggs with a range of blue and yellow square sizes, robins were more likely to reject model eggs with larger spatial chromatic contrasts (i.e., model eggs with larger squares) (Luro et al., 2020), indicating both spatial and chromatic contrast together may represent a visual cue for robins when making egg rejection decisions in the presence of maculation and its contrast against the eggshell's ground coloration (also see Dainson et al., 2017).…”

“…Robins almost always reject natural whitish and spotted brown‐headed cowbird eggs (Rasmussen et al., 2009; Rothstein, 1982). Robins also overwhelmingly reject model eggs with cowbird‐like white/beige ground colors (Croston & Hauber, 2014a; Luro et al., 2018; Rothstein, 1982) and eggs with heavy, brown maculation (Carmody et al., 2016; Dainson et al., 2017; Luro et al., 2020; Rothstein, 1982). Even though robins seem to rely less on subtle shifts in egg size as a sensory cue for egg rejection (Igic et al., 2015), cowbird‐sized eggs nonetheless elicit high rejection rates (Carmody et al., 2016; Luro et al., 2018).…”