Half-Blind to the Risk of Predation

Abstract

Blinking serves several functions in animals, but it comes at the cost of intermittent blindness. Blinking can occur spontaneously, but it is commonly associated with head movements. As feeding animals often need to move the head down repeatedly to gather resources, intermittent blindness might represent a hitherto unappreciated cost of feeding. In addition, this cost might also be more prevalent in larger groups as feeding effort typically increases with group size. In chickens (Gallus gallus domesticus), blinks associated with head movements occurred at a high frequently during feeding bouts. While blinks tended to be short, the amount of time spent blinking was close to 50% when feeding and increased with group size. By contrast, time spent blinking was much lower when birds simply monitored their surroundings between feeding bouts. Intermittent blinking at this scale when feeding is likely to decrease the ability to detect predation threats in a timely fashion and to monitor neighbors effectively.

Wind Increases Blinking Behavior in Great-Tailed Grackles (Quiscalus mexicanus)

“…Blinking impairs visual processing in humans (Volkmann et al, 1980;Bristow et al, 2005;Hoppe et al, 2018) but no empirical studies have tested whether it also impairs visual processing in birds or other species. However, indirect evidence suggests that blinking behavior in birds interferes with visual processing because (1) birds strategically inhibit their blinks (Cross et al, 2013;Yorzinski, 2016;Beauchamp, 2017) and (2) the nictitating membrane used for blinking is only semi-transparent in many avian species (Sivak, 1980). We tested the influence of wind on blinking behavior using captive great-tailed grackles (Quiscalus mexicanus), a songbird species that often inhabits open areas and is native to North and South America (Johnson and Peer, 2001).…”

“…We tested birds when their heads were restrained and unrestrained. Because blinks are often associated with head movements in other species (Evinger et al, 1994;Gandhi, 2012;Yorzinski, 2016;Beauchamp, 2017), we wanted to test the impact of windy conditions on blinking behavior while controlling for the possible confounding effects of head movements. We expected that the birds' blinking behavior would increase when they were exposed to the simulated wind.…”

Blinking behavior in great‐tailed grackles (Quiscalus mexicanus) increases during simulated rainfall

“…Their blinking behavior was generally similar regardless of whether the birds' heads were restrained or not. Previous work has found that birds (Beauchamp, 2017;Yorzinski, 2016) and…”

“…Their blinking behavior was generally similar regardless of whether the birds’ heads were restrained or not. Previous work has found that birds (Beauchamp, ; Yorzinski, ) and primates (Evinger et al, ; Gandhi, ) often blink when they move their heads, so it was possible that the grackles would have exhibited increased blinking behavior when their heads were unrestrained. However, the grackles did not necessarily exhibit many head movements even when their heads could move freely.…”

“…Blinking behavior is necessary to maintaining clear vision but individuals likely experience impaired visual processing during blinks (Bristow, Haynes, Sylvester, Frith, & Rees, 2005;Hoppe, Helfmann, & Rothkopf, 2018;Volkmann, Riggs, & Moore, 1980). Indirect evidence suggests that blinking behavior in birds interferes with visual processing because birds strategically inhibit their blinks (Beauchamp, 2017;Cross et al, 2013;Yorzinski, 2016) and the nictitating membrane used for blinking is only semi-transparent in many avian species (Sivak, 1980). The impact of simulated rainfall on blinking behavior was tested using captive great-tailed grackles (Quiscalus mexicanus), a songbird species that often inhabits open areas in regions with periodic rainfall (Johnson & Peer, 2001).…”