Cognition and the Brain of Brood Parasitic Cowbirds
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Western University Scholarship@Western Psychology Publications Psychology Department 3-1-2019 Cognition and the brain of brood parasitic cowbirds. David F Sherry Mélanie F Guigueno Follow this and additional works at: https://ir.lib.uwo.ca/psychologypub Part of the Behavioral Neurobiology Commons, Biology Commons, and the Psychology Commons Citation of this paper: Sherry, David F and Guigueno, Mélanie F, "Cognition and the brain of brood parasitic cowbirds." (2019). Psychology Publications. 175. https://ir.lib.uwo.ca/psychologypub/175 Integrative Zoology 2019; 14: 145–157 doi: 10.1111/1749-4877.12312 1 REVIEW 1 2 2 3 3 4 4 5 5 6 6 7 Cognition and the brain of brood parasitic cowbirds 7 8 8 9 9 10 10 11 David F. SHERRY1 and Mélanie F. GUIGUENO2 11 12 12 1 2 13 Department of Psychology, Western University London, Ontario and Department of Natural Resource Sciences, McGill University, 13 14 Montreal, Quebec, Canada 14 15 15 16 16 17 17 18 18 19 Abstract 19 20 Cowbirds are brood parasites. Females lay their eggs in the nests of other species, which then incubate the cow- 20 21 bird eggs and raise the young cowbirds. Finding and returning to heterospecific nests presents cowbirds with 21 22 several cognitive challenges. In some species, such as brown-headed cowbirds (Molothrus ater), females but 22 23 not males search for and remember the locations of potential host nests. We describe recent research on sex dif- 23 24 ferences in cognition and the hippocampus associated with this sex difference in search for host nests. Female 24 25 brown-headed cowbirds perform better than males on some, but not all, tests of spatial memory and females 25 26 show a pattern of adult hippocampal neurogenesis not found in males or in closely related non-parasitic birds. 26 27 Because of the apparent specialization of the hippocampus, brown-headed cowbirds may be a good model in 27 28 which to examine spatial information processing in the avian hippocampus and we also describe recent research 28 29 on the spatial response properties of brown-headed cowbird hippocampal neurons. 29 30 30 31 Key words: adult neurogenesis, brood parasites, cowbirds, hippocampus, sex differences, spatial memory 31 32 32 33 33 34 34 35 35 this brood parasitic way of life. Selection should be no 36 INTRODUCTION 36 less intense on brood parasites than on non-parasites, 37 37 Brood parasites avoid the costs of nest building, incu- and non-parasites possess a vast range of behavioral, 38 38 bation and parental care by laying their eggs in the nests cognitive, physiological and neural specializations that 39 39 of other birds. For obligate brood parasites, there is no promote successful reproduction (Lack 1972; Williams 40 40 other path to successful reproduction. It therefore seems 2012; Deeming & Reynolds 2016). The present paper 41 41 reasonable to suppose that natural selection has acted describes cognition and the brain of brood parasites, fo- 42 42 on behavior, cognition and the brain of brood parasites cusing on recent research on sex differences in spatial 43 43 to increase individual reproductive success achieved by memory and the hippocampus of cowbirds. 44 44 45 There are 6 major groups of interspecific brood par- 45 46 asites: cowbirds, honeyguides, parasitic finches, Old 46 47 World cuckoos, New World ground-cuckoos, and 1 spe- 47 48 Correspondence: David Sherry, Advanced Facility for Avian cies of parasitic duck (Davies 2000). To succeed in hav- 48 49 Research, Department of Psychology, Western University, ing heterospecific parents incubate their eggs and raise 49 50 London ON N6G 1G9, Canada. their young, brood parasites have to solve a number of 50 51 Email: [email protected] problems that non-parasites do not, and many of these 51 © 2018 International Society of Zoological Sciences, Institute of Zoology/ 145 Chinese Academy of Sciences and John Wiley & Sons Australia, Ltd D. F. Sherry and M. F. Guigueno 1 problems are cognitive: brown-headed cowbirds (Jetz et al. 2008). Brown-head- 1 2 1. Find potential host nests. Most songbird hosts of ed cowbirds probably do not achieve a 10-fold repro- 2 3 cowbirds take a great deal of care to conceal their nests ductive advantage compared to non-parasites from the 3 4 to reduce predation on eggs, nestlings and incubating large number of eggs they produce (Woolfenden et al. 4 5 adults, and to reduce brood parasitism. 2003), but their brood parasitic behavior does require 5 6 2. Remember and revisit potential host nests. Hav- finding and returning to a very large number of potential 6 host nests. 7 ing found a nest, female cowbirds return to it later, ei- 7 8 ther to monitor host clutch completion, to lay one of her Female brown-headed cowbirds search for host nests 8 9 own eggs, or to remove a host egg (Sealy 1992; Scar- in which to lay their eggs but males do not. This di- 9 10 damaglia et al. 2017). vision of labor between the sexes does not occur in 10 all cowbirds. In the South American screaming cow- 11 3. Determine the stage of host clutch completion. Fe- 11 bird (Molothrus rufoaxillaris Cassin, 1866) males and 12 male cowbirds prefer to lay in host nests in which a few 12 females search for host nests together. However, in 13 eggs have been laid but the clutch is not yet complete 13 brown-headed cowbirds, search is performed by fe- 14 to ensure that her egg hatches with or before the host’s 14 15 males alone and it occurs some time before females ac- 15 eggs (Sealy 1995). tually lay their parasitic egg. Females often lay at dawn, 16 4. Monitor the host’s response to brood parasitism 16 17 or earlier (Neudorf & Sealy 1994), and so they are not 17 (Hoover & Robinson 2007) and the reproductive out- searching at this time for potential host nests. They are 18 18 come of the cowbird’s brood parasitic behavior (Louder going to a nest they have previously discovered. After 19 19 et al. 2015). laying, they may spend the rest of the morning search- 20 20 Some of the cognitive processes involved in brood ing for host nests in which to lay eggs on subsequent 21 21 parasitism have been examined in current research. days (Scott 1991), or re-visiting nests they have already 22 22 These include spatial memory, especially sex differenc- discovered to check on the progress of host egg laying 23 23 es in spatial memory (Astié et al. 1998; Guigueno et al. and clutch completion (White et al. 2009). Females find 24 2014, 2015; Astié et al. 2015), numerical ability (White nests by flying into understory vegetation to flush in- 24 25 et al. 2007, 2009) and specializations in the brain that cubating hosts or by watching the nest building behav- 25 26 accompany these cognitive specializations (Sherry et ior of hosts from the canopy or the forest floor (Nor- 26 27 al. 1993; Reboreda et al. 1996; Clayton et al. 1997; man & Robertson 1975). Females are choosy about the 27 28 Nair-Roberts et al. 2006; Guigueno et al. 2016). state of the nest in which they lay their egg. They prefer 28 29 29 The research we describe examines how the brood to lay in a nest that already has some eggs in it, but not 30 30 parasitic mode of reproduction has modified cogni- too many. In fact, female brown-headed cowbirds pre- 31 fer to lay in a host nest with 3 eggs in it, but it is equally 31 tion and the brain of brood parasites. We describe sex important that it be an active nest to which the host par- 32 differences in spatial memory that have been found 32 ent is still adding eggs. David White and his colleagues 33 in brown-headed cowbirds and sex differences in the 33 found that day-to-day changes in the number of eggs in 34 brain, specifically in the size of the hippocampus and 34 a host nest can have a major effect on how likely a fe- 35 in adult hippocampal neurogenesis, that are associat- 35 male brown-headed cowbird is to place one of her own 36 ed with these sex differences in spatial memory. Given 36 eggs in that nest (White et al. 2009). This preference 37 the apparent specialization of the brown-headed cow- 37 for nests with a daily change in egg number occurs be- 38 bird hippocampus, we also describe recent research ex- 38 39 cause a nest in which the number of eggs is unchanging 39 amining the spatial response properties of neurons in the is a nest in which the host has ceased laying and begun 40 40 brown-headed cowbird hippocampus. incubation. If incubation has already begun, there is re- 41 41 ally no way to determine when those eggs are likely to 42 42 SEX DIFFERENCES IN SPATIAL hatch. If they hatch before the cowbird egg has complet- 43 ed development, the cowbird egg will be abandoned and 43 44 MEMORY never hatch. In contrast, a nest to which the host is still 44 45 45 Female brown-headed cowbirds [Molothrus ater adding eggs is a nest in which incubation has not yet be- 46 46 (Boddaert, 1783)], parasitize over 200 different spe- gun, and a cowbird egg placed in such a nest will hatch 47 47 cies of host and can lay up to 40 eggs in a breeding sea- along with or even before the host’s young. 48 48 son (Scott & Ankney 1980, 1983; Rothstein et al.