The Mauritius kestrel is a scrappy bird but will it survive humans?
The Mauritius kestrel (Falco punctatus) was once a success story in wildlife conservation. In 1974 the species was just down to just four surviving individuals, including a single breeding pair. At the time, it was called the “world’s rarest bird.” An intensive management program included captive breeding, construction of nest boxes, guarding of nests against predators, and more. By the end of the 1994 breeding season, twenty years later, the population numbered some 280 individuals. By 2000, the total population was estimated to include 500-800 birds, comprised of almost 200 breeding pairs. One estimate in 2005 suggested that there were almost one thousand birds flying the skies of the island. Even if that’s an overestimate, as some suspect, it’s still a tremendous increase when compared with 1974.
The original decline has been pinned to the use of agricultural pesticides. Since they rebounded, they have also had to contend with predation from invasive black rats, crab-eating macaques, Indian mongooses, and (obviously) domestic cats. But their main enemy is now habitat loss.
Mauritius kestrels nest and hunt in the tropical forest canopy, but most of the island’s forests have been cleared for agriculture. Just three percent of the original forest cover now remains. Without the concealment offered by the canopy, the birds are easier picking for their predators. And their main source of food, geckos of the genus Phelsuma, aren’t abundant in agricultural fields. That’s a problem when geckos comprise 80% of their typical diet. That means less food for mom and dad, and less food for their newly hatched chicks.
Still, all may not be lost for the Mauritius kestrel. Using 23 years of longitudinal data on the species, environmental scientist Samantha J. Cartwright of the University of Reading, together with colleagues from the Mauritian Wildlife Foundation, discovered that they may be adapting to the human-caused changes in landscape. As forests give way to sugarcane fields, some kestrels speed up their reproduction.
The researchers compared the evolutionary fitness of female birds born in areas of high agriculture (where greater than 30 percent of their territory was farmland) to those born in areas of 100% forest cover. Surprisingly, the two groups’ fitness was comparable. It turns out that those females born in areas of high human activity were more reproductively successful earlier in life, and less successful as they aged. To compensate for their shorter lifespans, they begin breeding early. They die younger than their counterparts who grew up in better neighborhoods, but they have just as many offspring. That’s in contrast to the “silver-spoon effect” for other species, in which those born in a higher-quality environment have higher fitness. The finding was the same whether Cartwright relied on the number of chicks that the females successfully fledged or the number of chicks who themselves fledged chicks.
That’s the good news.
The bad news, as is so often the case for island birds, is that they’re suffering from inbreeding and numbers are beginning to decline once again. By 2012, the population had decreased to an estimated 400 individuals, found in just three parts of the island. The sub-population on the northern side of the island is probably extinct, and while the eastern population is holding stable with forty breeding pairs, the southwestern population continues to decline.
Cartwright points out that the long-term effect of human activity on wildlife is woefully under-studied. “The patterns we report could be widespread but remain poorly documented due to the short-term nature of most studies that attempt to quantify only the immediate impact of habitat change on fitness traits,” she writes. In addition, many studies “[ignore] the fact that changes to reproductive output and survival may be delayed in time and observed in different habitats from those ultimately driving the changes,” she adds.
Humans are changing the face of the planet in innumerable ways and in many cases wildlife suffers. But some species, like the Mauritius kestrel, are highly adaptable and have proven themselves remarkably resilient in the face of the so-called anthropocene epoch.
Will the scrappy bird ultimately survive in the long run? It’s not yet clear. – Jason G. Goldman | 5 March 2014
Source: Cartwright S., Nicoll M.C., Jones C., Tatayah V. & Norris K. (2014). Anthropogenic Natal Environmental Effects on Life Histories in a Wild Bird Population, Current Biology, 24 (5) 536-540. DOI: 10.1016/j.cub.2014.01.040
Image: Samantha J. Cartwright, used with permission.
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