Are Visual Stimuli Enriching for Three Species of Odontocetes in Managed Care?

In many species, females have evolved to choose carefully between potential mates, generally being the pickier sex (Trivers ; Clutton‐Brock et al. ; Kenrick et al. ). This is because females must guard their reproductive resources more than males: they invest more into each gamete, and often provide more parental care (Trivers ; Clutton‐Brock et al. ; Kenrick et al. ). In their natural environments, choosing a high‐quality mate thus benefits females' overall reproductive success, doing so both , by improving their survival or fecundity (via better territory, resources or parental care), and by improving offspring fitness via these beneficial traits (Williams ; Taylor and Williams ; Reynolds and Gross ; Kirkpatrick and Ryan ). Consequently, females have evolved to utilize various cues to assess male quality when choosing mates. Females prefer condition‐dependent cues indicative of good nutritional status and low stress (e.g., good health, heavier body weights, brighter coloration, more intricate ornamentation, more complex songs: Parsons ; Forstmeier ; Adrian et al. ; Clutton‐Brock and McAuliffe ), and thence better territories or access to resources, or good genotypes that can be passed to offspring (Jennions and Petrie ). The implications of these mate‐choice dynamics extend beyond the wild into captive conditions, because suboptimal housing (e.g., crowded, small and/or barren conditions) can adversely affect the male cues that females prefer. For example, females sometimes prefer cues indicating high testosterone, such as large testes (Jones et al. ) and long anogenital distances, AGDs (Ophir and Delbarco‐Trillo ), since high testosterone may be associated with the potential for more vigorous or competitive offspring; yet testosterone is stress‐sensitive (e.g., Deviche et al. ) and can therefore be reduced in males housed in small, barren cages compared to those in large, well‐resourced (WR) ‘enriched’ ones (e.g., mice: Nevison et al. ; American mink []: Díez‐León et al. ). Females also often prefer males with relatively low levels of circulating glucocorticoids (e.g., zebra finches [], Roberts et al. ; and even humans [Moore et al. ]). However, crowded, small and/or barren housing conditions can elevate this hormone (e.g., North American clouded leopard []: Wielebnowski et al. ; red pandas []: Khan et al. ). Turning to physical cues, females often prefer symmetrical males, as seen in zebra finches (Swaddle and Cuthill ) and again humans (Koehler et al. ; Gangestad et al. ), because symmetry indicates abilities to cope with challenging conditions (e.g., Swaddle and Cuthill ; Özener ). In sub‐optimal housing, however (e.g., grid floors and single housing for Lewis rats: Sørensen et al. ; small, barren cages for mink: Díez‐León et al. ) male symmetry declines. Finally, females often prefer larger or heavier males (e.g., Forstmeier ). But again, perhaps because weight can decline with stress (e.g., Jean‐Faucher et al. ), males housed in small, barren cages may become smaller and lighter those in large, WR ‘enriched’ ones (e.g., American mink: Díez‐León et al. ). Given such examples, poor male welfare may well reduce their success with females. It is thus not surprising that, in the few studies to investigate this, poor captive housing harms males' success with females. In one study of stocking density in Mexican fruit flies () (Díaz‐Fleischer et al. ), and four studies of WR ‘enriched’ housing on fruit flies () (Dukas and Mooers ), zebrafish () (Lavery et al. ), rats (Mitra and Sapolsky ) and mink (Díez‐León et al. ) males raised in higher stocking densities or smaller, more barren housing conditions were less successful with females. Thus, fruit flies experiencing lower stocking density (Dukas and Mooers ), and WR male mink (Díez‐León et al. ) and fruit flies (Dukas and Mooers ), obtained more matings than did males housed in poorer conditions. While this could reflect increased male libido, two studies further showed that housing can affect male attractiveness per se, in mate choice tests where females can choose freely. In choice arenas, female rats preferred to spend time near WR‐raised males over males raised in conventional barren cages (Mitra and Sapolsky ); and in T mazes, female zebrafish similarly preferred to spend time near WR males over males raised in barren tanks (Lavery et al. ).