The Three-Minute Outdoorsman: Wild Science from Magnetic Deer to Mumbling Carp

33. Vigilance in Ducks

t h e t h r e e - m i n u t e o u t d o o r s m a n 128 fer. In hundreds of instances a discovery in one field has removed a roadblock to progress in another. Granted, not all research is deemed important by other experts, and one way this is determined is via the funding process. Evaluation of the value of research ought to be done by persons qualified to judge. In the case of Brennan and colleagues, their research was extremely insightful and valuable to the field of animal behavior, and their critics were badly misinformed. 33 vigilance in ducks more than meets the eye(lid) Several potential advantages accrue to individuals who live in flocks. An obvious advantage is being able to share guard duty. If you trust your flock mates, you can sleep or not spend a lot of time watching for predators as long as someone else is on duty, being vigilant. Then later you take your turn at watch, and over time, you are more efficient as an individual because of the sharing of guard duty among the flock members. Everyone must be “honest” for this to work. No slackers or cheaters allowed. Although this strategy might seem simple, rules for flock living aren’t necessarily straightforward. Researchers who study flocking behavior have made many insightful observations about how individuals change their behaviors in flocks of differing sizes. For example, imagine that you’re in a small flock. Fewer eyes mean that you must spend more time watching for predators and less time feeding or sleeping. This would argue, seemingly, for being in a larger flock with more (potentially) cooperating birds. However, more birds in the flock usually means more fighting and perhaps less food per capita. Thus, there’s a tradeoff between flock size and the advantage that accrues to individuals in terms of reduced I N T H E W A T E R 129 guard duty. Bigger isn’t necessarily always better when it comes to flock size. Behavioral biologists are pretty sure this is true because of experiments with flocking birds and their predators. For example, if there were hardly ever any predators, a flock would be safe with just a couple of sentries. However, biologists can manipulate the apparent predator level by using either trained hawks or models. If flock-living birds perceive a greater-than-normal number of predators (compliments of researchers), flock size predictably increases, as more eyes are needed to maintain a certain level of vigilance. There is probably a certain distance at which a predator needs to be detected to provide enough time for the alarm to spread, the flock to scramble, take off, and confuse the predator. If the warning comes too late, the flock will have one less set of eyes, poor though they might have been. Anyone who has watched a war or cowboy movie knows that the guy in charge tells the troops who has the first watch, second watch, and so on, and predictably one sentry falls asleep at a critical time (but that’s Hollywood). How do birds decide who is on watch? Or for that matter, if you were a bird, how would you even know whether another individual was doing his or her job? I’d bet that most of us would pretend to be asleep and then sneak a peek to see if the appointed guard was watching out, loafing, or showing off. A 2012 scientific paper in the British journal Ibis titled “Consistent Contrast between Eyelid and Iris Brightness Supports a Role for Vigilance Signalling in Ducks,” by Matthieu Guillemain and colleagues, provided some interesting insights into the potential vigilance behavior of ducks. They observed forty-three duck species at a zoological park in Villars-les-Dombes in eastern France. These species included seventy-one plumage “morphs”— some of the species were sexually dimorphic, meaning that males and females had different plumages. The authors had the seemingly odd goal of determining whether the eye and the eyelid were contrasting in color. t h e t h r e e - m i n u t e o u t d o o r s m a n 130 At first glance, their goal might indeed seem like some arcane academic exercise. But their observations were exceedingly relevant to this question: if you’re a duck in...