How The Resilient Mauritius Kestrel Changed Its Life Pattern To Survive Habitat Loss
Mauritius kestrels, a species of vulnerable birds, once flourished happily alongside the dodo bird on their African island, 1,200 miles into the Indian Ocean. But that was before colonization. By 1700, Dutch deforestation and agriculture had killed off the last known dodo bird in an infamous case of human encroachment. After the French and then the British took over, conditions did not improve. In 1974, exactly four Mauritius kestrels were thought to exist.
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New research shows that these birds, which have since recovered, are even more resilient than we thought: To maintain healthy reproductive levels, Mauritius kestrels are actually speeding up their biological clock. To hedge against the likelihood of dying younger, they're reproducing younger, according to a study from the University of Reading, announced Thursday and published in the journal Current Biology.
"This adaptive, plastic response is a testament to how resilient this species is," says Samantha Cartwright, the lead author on the study, in a statement. "It has narrowly avoided extinction in the 20th century and is now persisting in a landscape very different from what it would have originally evolved to occupy."
The landscape these days is a lot less forest and a lot more sugar cane fields. Habitat loss and over-exploitation through hunting and harvesting are the main causes of biodiversity loss globally. In the 35 years leading up to 2005, worldwide biodiversity has fallen by more than a quarter, according to the World Wide Fund for Nature. In Mauritius that downward trend began long before 1970. The dodo bird disappeared around the beginning of the 18th century, but deforestation for agriculture continued. Today, only 2 percent of original Mauritius forests remain.
In the 1950s and 1960s, pesticides containing DDT came into use to ward off mosquitoes bearing malaria. The chemicals were an insidious poison for Mauritius kestrels — it caused egg shells so thin they broke when mothers sat on them in incubation. Researchers in the late 1950s could find only a couple dozen birds in a mountainous park in the more remote, southern part of the island. A subsequent census in 1974 came up with a total population of four. Through captive rearing and intense conservation efforts, environmentalists helped push their numbers back into the hundreds.
But the new research shows the birds have a talent for helping themselves, as well. By analyzing 23 years of data about Mauritius kestrels — which have been monitored unusually closely over the years — the Cartwright found that females that lived in places threatened by manmade disturbances were more likely to die younger. That part wasn't surprising. What was surprising was that these females started making babies at a younger age than females in unthreatened habitats.
"We found that birds from both types of habitat still ultimately produce the same number of offspring in a lifetime," Cartwright says. "The strategy is a good one: breeding when younger compensates for the increased risk of dying sooner." In the paper, the authors write that adaptations like this are probably more common than we think but that most species aren't as well documented over such a long period of time as the Mauritius kestrel.
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