Bright colors increase the risk of predation, especially in birds where males alternate seasonally between cryptic and conspicuous plumages. So how do brightly colored male birds protect themselves from predators?
I ran across a sweet little paper that will make behavioral ecologists tingle in delight. Not only is this paper based on a really lovely experimental design, but it focuses upon a cute little bird species that has spectacular breeding plumage. So there’s something here to satisfy nearly everyone.
Conspicuous plumage attracts the attention of predators
Intuition indicates (and research shows) that conspicuous colors attract the attentions of predators. Despite this, there are very few published studies demonstrating that animals are aware of their own conspicuousness and alter their behavior to reduce their risk of being noticed (but read this, and this). So far, there are no published studies showing the behavioral effects of conspicuous colors when they are used for signalling: in that situation, does a conspicuous animal alter his behaviors to avoid becoming a snack? A group of Australian scientists decided to find out by studying a tiny bird species, the superb fairy-wren.
Superb fairy-wrens, Malurus cyaneus, are sexually dichromatic songbirds that are common in southeastern Australia and on the island of Tasmania. Immature birds, females and non-breeding males have brown-grey upperparts, pale grey underparts and a white throat. Adult males can be identified by their long blue tails whilst adult females have a ring of bright orange feathers around their eyes.
But when breeding season rolls around, there is no question as to gender: adult males assume brilliant blue plumage; a bright blue head, ear coverts, mantle, and tail, with a black mask, neck, and back, and a black or dark blue throat patch. Their spectacular plumage signals their genetic quality to the discerning eyes of females.
Superb fairy-wrens are sedentary territory-holding birds that live in groups comprising a dominant pair, and often include several male helpers. Although the dominant pair is socially monogamous, they’re not very faithful: extra-pair paternity is very high — often up to 70% of the offspring in a population (ref). Females don’t appear to be choosy about their social partner, but they do select extra-pair mates that moult into their blue plumage early and stay blue the longest — usually 11–12 months of the year.
Males moult twice per year, alternating between cryptic brown and conspicuous blue-and-black plumages. Since male fairy-wrens don’t all moult into breeding plumage at the same time, behaviors of brown and blue individuals can be compared at the same time of the year, and seasonal effects on behavior can be controlled for. Further, because there is a population of individually color-banded birds living in Lysterfield Park in Victoria, Australia, field studies of these birds could be conducted that compared behaviors of individuals whilst they were brown or blue. This also served as a useful control for individual differences due to personality and to a variety of social factors.
Bright blue plumage makes male fairy-wrens flighty
Superb fairy-wrens produce different alarm calls for different sorts of danger: they produce high-frequency four-element “high danger” calls when they see aerial predators, and they also produce a low-frequency single-element “low danger” call. Fairy-wrens show a range of responses to low danger alarm calls, but they almost always flee immediately upon hearing a high danger alarm.
The sex, plumage color (brown or blue) of the focal bird, and their pre-playback activities were noted. These activities included foraging, acting as a sentinel, preening, resting or singing. The numbers of bystander fairy-wrens was recorded as well as their colors, and their distance from the focal bird.
When hearing alarm call playbacks, male superb fairy-wrens in blue plumage responded more strongly than did brown birds, and were more likely to flee, regardless of their prior activities (Figure 1).
Blue birds were more likely to flee in response to low danger alarm calls and remained hidden longer after fleeing, and spent more time scanning their surroundings. Although blue birds spent more time foraging under cover, they actually spent less time overall on foraging when compared to brown birds.
Also interesting (to me, anyway) were the responses of bystander birds: after responding to a high danger alarm call, group members emerged from hiding sooner and spent less time scanning their surroundings when a blue male was nearby. Did they perceive the blue male as a decoy for potential predatory attacks? Or were they relying on the hypervigilant blue males to warn them of potential danger?
This study shows us that conspicuous colors do increase predation risk, independent of other factors, and it also shows us that conspicuous birds are aware of their greater danger to attack by a predator. So although these boldly colored male birds look like show-offs to us, they actually are cowards.
Alexandra McQueen, Annalise C. Naimo, Niki Teunissen, Robert D. Magrath, Kaspar Delhey and Anne Peters (2017). Bright birds are cautious: seasonally conspicuous plumage prompts risk avoidance in male superb fairy-wrens, Proceedings of the Royal Society of London B: Biological Sciences, published online on 28 June 2017 ahead of print | doi:10.1098/rspb.2017.0446
Mark Briffa, and Claire Twyman (2010). Do I stand out or blend in? Conspicuousness awareness and consistent behavioural differences in hermit crabs, Biology Letters, 7:330–332 | doi:10.1098/rsbl.2010.0761
David J. Green, Helen L. Osmond, Michael C. Double, and Andrew Cockburn (2000). Display rate by male fairy-wrens (Malurus cyaneus) during the fertile period of females has little influence on extra-pair mate choice, Behavioral Ecology and Sociobiology, 48(6):438–446 | doi:10.1007/s002650000258
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Originally published at Forbes on 27 June 2017.