Исследователи отслеживают миграцию грифов-каракаров с помощью GPS-трекеров

The turkey vulture is not the most handsome bird, with its red featherless head and chicken-like feet — not to mention its penchant for eating all things dead and rotting. Raptor cousins like sharp-taloned eagles or swivel-headed owls might get all the glory, but when it comes to graceful gliding and cleaning up fatalities, nobody does it better than Cathartes aura — nature’s great purifier. “I think they’re gorgeous — and so important — but then I’m a little biased,” says Cara Herrington, a PhD candidate at the University of Victoria and expert on the scavengers at The Raptors sanctuary north of Duncan. The turkey vulture is designed for what it does best. The clean head keeps down the bacteria when it buries its face in dead things, and it defecates on its wide feet and featherless legs to cool itself. “They’re so important for removing biological waste and are the stopping point of disease transmission,” said Herrington, who says turkey vultures can ingest things like botulism, anthrax and rabies that can spread to other animals. Herrington says turkey vultures have super-charged stomach acids — “almost as strong as battery acid” — and an intense gut microbe that destroys anything that goes into their digestive systems. “And they’re not excreting that outwards, which is really quite amazing.” And if you think you’re seeing a lot more turkey vultures soaring on the thermals around the Island these days, researchers will say you’re correct. The turkey vulture has been expanding its northern range for decades in North America. Nowhere is their presence more evident than on Vancouver Island, where they’ve been feeding and nesting from tip to tip over the past few decades. According to new research from the Rocky Point Bird Observatory, counts of turkey vultures at a particular spot in the Metchosin area have increased by 300% over the past 25 years. Nobody’s quite sure exactly how many are on the Island, though it’s estimated to be in the thousands. And they are staying longer, delaying their annual migrations for longer periods to take advantage of increasingly higher temperatures and warmer air that sustains their hunting and flight, possibly due to climate change, according to Camosun College professor Daniel Donnecke, an avid birder and co-author of a peer-reviewed study published in June in the Journal of Raptor Research. Donnecke, a chemistry professor, teamed up with retired McGill University biology professor and Brandon University’s Stefanie LaZerte to crunch turkey-vulture daily counts by the observatory from 1999 to 2023 at a unique gathering spot near Metchosin. The counts were made in the fall at a spot where groups of the turkey vultures — called kettles — gather before making the 18-kilometre crossing of the Strait of Juan de Fuca to Washington state on their annual migration to Mexico, Central America and as far south as Venezuela. It’s something vultures on the mainland don’t have to worry about, but the Island birds have to wait for the right winds and conditions. Turkey vultures aren’t really built for wing-flapping flying. Rather, they catch thermal updrafts of warm air and wind shears for distance glides so they don’t have to expend a lot of energy. The vultures need warm air columns and optimal conditions to cross the water. “Their special adaptation is basically this gliding low-energy-expenditure flight to search for food, so they need these rising air columns for that and to safely make a crossing of a large body of water,” Donnecke said. “They’re not really active on days where it’s raining, foggy or overcast.” Birds plucked out of the water Donnecke said kettles of vultures numbered a few dozen individual birds in 1999 but have grown to up to 2,500 most recently during daily fall counting around Metchosin. “We anticipated that counting the kettles would provide useful information on the timing of migration and abundance of the species, but were surprised to see how strong and clear the pattern was,” Donnecke said. Herrington said turkey vultures will kettle at other points, like East Sooke Park and near French Creek, to make water crossings. Part of her PhD dissertation is getting an idea of the weather conditions the birds are relying upon to cross, such as a specific wind direction or speed, or whether there are other factors involved. “People think ‘Well, it’s a bird … it should just be able to fly across,’ ” Herrington said. “But they’re so adept at this sort of passive form of flight that they just don’t have that sort of physical, mechanical strength or stamina for that long-term wing flapping to maintain altitude. “Their beautiful form of flight is almost a hindrance when they get to a barrier such as this.” Herrington has heard stories of fishermen plucking the birds out of the water on the Washington side and knows of at least one case where a turkey vulture splashed down far off Metchosin and was brought to shore by a whale-watching vessel. The turkey vultures can also make false starts, Herrington said. In 2024, she watched some trying to make the crossing and then changing their minds and struggling to make it back to shore at low altitude. Another vulture barely made it back to land, and at the last minute caught an updraft and sailed higher. “I was ready to take off my binoculars and go in … that’s how low they were.” Herrington said it’s likely some don’t make the crossing, but how many isn’t known. The fact that they are staying longer every year because of warmer weather and a steady food supply in forests, along roads and in intertidal zones might explain why we’re seeing more of them, she said. “If you’ve got great food sources here and the weather is still good, then why not [delay]?” said Herrington. “Migration is such a dangerous thing. For every bird species, it’s such a huge energy expense. So, if you can stay and get the sustenance that you need before you absolutely have to get going, then why wouldn’t they?” Donnecke said the turkey vulture is relatively understudied and underappreciated. “When people ask why we’re counting turkey vultures, we find that if we explain their ecological role, specialized adaptations for soaring and the reason why kettles form on southern Vancouver Island, people respond with a much more positive view of the species.” More roadkill a factor in growing population The Ontario-based Canadian Raptor Conservancy says turkey vultures are the most abundant vulture in the Americas, with a global population of 4.5 million individuals. Scientists believe they are steadily increasing across their range, likely as a result of some combination of reductions in lead contamination and pesticides in the environment, increasing deer populations and more available roadkill along expanding highway and road systems. Their breeding season starts in March, peaks in April and May and continues into June. Herrington said there are several nesting sites on the Island, some of which she monitors with remote cameras. They usually produce two eggs without building a nest, nesting in caves and rock outcroppings, fallen hollow trees or in thickets. Herrington and Gill Radcliff, The Raptors’ research director, used a research grant to fit 13 turkey vultures with GPS solar-powered trackers in 2022 for real-time insights into their locations and daily patterns. That’s how they found nesting sites in remote mountain cliffs and caves, and were able to see where they go in spring and summer and during the winter months in Mexico. “They have very high site fidelity, because there’s just such a benefit to that in that if you’re familiar with the area, you know where the safe places are, you know where the good food’s going to be. It’s not a guessing game year after year.” Herrington said. The raptor conservancy said turkey vultures lack a syrinx, the vocal organ for birds, and the only sounds it makes are grunts or low hisses. Its primary defence is regurgitating semi-digested carrion, which can sting the eyes of a potential predator at nesting sites. Donnecke said turkey vultures have very few natural predators and will feed on carrion with other eagles and mammals such as wolves. At nesting sites, he said, chicks will hiss, and the sound deters most intruders.