18 Mar Birds That “Hire” Bodyguards
Long-legged birds—such as egrets, herons, ibises, spoonbills and storks—in the Florida Everglades have discovered that having a big, bad neighbor provides some substantial benefits.
Going to places that are quite different from home, stretching your physical limits or trying on unfamiliar, cultural experiences are all part of what makes an otherwise normal outing into a true adventure. Sometimes, all that newness can be tough on you. You take the steps you can to best protect yourself, and that’s when you begin to fantasize about what it must be like to have your own, personal bodyguard. Would you be braver? Would you be able to accomplish and succeed at more?
Nonhuman animals may have the same kinds of thoughts. In fact, several recent research studies show that some birds use big, bad neighbors as their personal security teams.
Mutual agreement: alligators and nesting birds
For animals living in the Florida Everglades, life is hard. Soaring temperatures, high humidity, thunderstorms and predators are on a long list of threats.
Trying to eke out a living in the Florida Everglades is very difficult for plants and animals. In the summer, the humidity can hit 100 percent; and most of the time, the temperatures are 95 degrees Fahrenheit or above. Severe thunderstorms are commonplace. In the winter, water levels drop, creating entirely different environments and landscapes. If you’re an animal, you either move or adapt. If, on top of those factors, you happen to be a nesting bird, you must also be constantly wary of predators.
Some of those birds are using a creative strategy to circumvent that danger. According to a study published on March 2, 2016, in the peer-reviewed Public Library of Science journal PLOS ONE, some nesting birds “employ” alligators as bodyguards.
To safeguard their nests and young chicks from Everglades predators, such as opossums and raccoons, some long-legged wading birds—such as egrets, herons, ibises, spoonbills and storks—will choose nesting sites above resident American alligators. To protect the nests from the alligators, the birds make sure to build them about five feet above the water, where the reptiles are unable to jump up and grab them.
Great blue herons build their nests about five feet above waters where alligators are found, protecting their young from mammalian as well as the reptile predators.
Protection services do not come without a cost, however. In the study, lead author Lucas Nell, an ecologist at the University of Georgia in Athens, and his colleagues compared the body condition of 20 alligators that lived near nesting colonies of wading birds in the Florida Everglades with 19 alligators that did not live near such colonies. To determine the alligators’ health, they took blood samples to assess their nutrient levels and measured their mass and length.
Results showed that the alligators that lived near wading-bird nesting colonies were in better condition than those in similar habitats without active colonies, independent of a range of environmental variables. And the difference was substantial. The mean body condition based on size and shape for colony-associated alligators ranked in the 63rd percentile, while that for noncolony alligators ranked in the 17th. A 6.5-foot-long alligator would, on average, weigh about 6.6 pounds more near a nesting colony than one in a similar habitat without a colony.
It seems that chicks that fall from the birds’ nests provide a food source for the alligators. Many colonially nesting birds lay more eggs than they can raise, and the birds typically adjust the size of their broods to fit available food levels by ejecting one to two chicks from each nest, alive or dead. That can provide the gators with a sizable amount of meat.
Alligators act as bird bodyguards, but they do demand “payment” for their services.
For the birds, the alligators seem to be the lesser of two evils. When raccoons and opossums invade colonies, the birds abandon them because the mammals eat all the eggs and chicks. Giving up one chick or two to an alligator to protect the many then makes sense.
Home security: hummingbirds and hawks
Birds not only use reptiles as bodyguards—some even use other birds.
In September 2015, a study published in the journal Science Advances revealed that black-chinned hummingbirds, weighing in at about 0.10 ounces (or a little more than a penny), that live in the canyons and river valleys of the Chiricahua Mountains in Arizona have learned to build their nests near goshawk and Cooper’s hawk nests to protect against Mexican jays. The jays—weighing 40 times more than the hummingbirds—are fond of eating hummingbird eggs.
The hawks are almost five times bigger than the jays and, in turn, often enjoy them for lunch. Hawks hunt by perching quietly and waiting for prey to pass below, bringing death from above. So, to avoid the raptors swooping down and surprising them, the jays only forage higher up in the forest canopy near hawk roosts. Thus, for a hummingbird, a cone-shaped safety zone exists below hawk perches, extending out about 984 feet.
In Arizona, goshawks protect black-chinned hummingbirds from Mexican jays.
Researchers found that hummingbird nests built within the safety zone the hawks provided yielded a survival rate of 19 percent versus the 6 percent survival rate seen with nests farther away from hawks. It got even better: building a hummingbird nest within a 560-foot radius of hawks boosted the survival rate up to 52 percent.
If getting a bodyguard fails, fake it
What do bodyguard-seeking birds do if no alligators or hawks reside nearby? It sometimes pays to fake it.
A paper published in the Proceedings of the Royal Society B on June 3, 2015, is the first to show that birds use vocal mimicry to scare predators away. Scientists from the Research School of Biology at the Australian National University found that the tiny brown thornbill of Australia imitates the hawk warning calls of a variety of birds to scare off predators threatening its nest, such as the larger pied currawong.
In Australia, pied currawongs, such as this one, prey on the smaller brown thornbills. ©James Niland, flickr
Currawongs are 40 times the size of a thornbill and will eat adults as well as nestlings. That’s why the much smaller brown thornbills have learned to mimic so many species, most much bigger than themselves.
These three studies show that if we want our conservation efforts to be effective, we’ll have to focus on entire ecosystems rather than on any one particular species. If a “bodyguard” animal should disappear, so, too, would the safekeeping of other animals vanish. Because as travelers and adventurers throughout the world have learned, you can sometimes succeed at more knowing there’s a backup for your bravery.
Here’s to your adventures, in whatever corner of the world you find them,
Candy
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