Tag Archives: birds of prey

Eagles migrate through bad weather to arrive in time to nest

(Physorg; 5 April 2017)
Migration is tough, and birds do everything they can to optimize it. How do factors like weather and experience affect the strategies they choose? A new study from The Auk: Ornithological Advances shows that older, more experienced Golden Eagles actually migrate in poorer weather conditions and cover less ground than their younger counterparts, but for a good reason—they’re timing their efforts around raising the next generation of eagles.
Adrian Rus of Boise State University (now at Australia’s University of Sydney), Todd Katzner of the USGS, and their colleagues studied GPS telemetry tracks to evaluate the migratory performance of almost 90 Golden Eagles in eastern North America and determine how performance related to season, age, and . Unsurprisingly, eagles flew faster and farther when they had strong tailwinds and thermals to help them along. What was counterintuitive, however, was that older eagles did not cover more ground than younger eagles despite their greater experience. Instead, older eagles migrated in poorer weather conditions and travelled more slowly.
The researchers believe this is because older birds face different pressures than younger birds. Even if the weather is bad and will slow them down, they need to start heading north earlier than young birds that aren’t breeding, because they have to get back to their breeding grounds in time to reclaim their territories and start nesting. “Younger eagles just need to survive the summer, so they can be choosy about when they travel north and only migrate when conditions are really ideal for fast soaring flight,” explains Katzner.

Lead author Adrian Rus, who worked on the study as an undergraduate, enjoyed the challenges involved in analyzing the migration data. “The best part about working on this project was using specialized software to visualize the golden eagle migrations and being able to pair it with meteorological data to answer my biological questions,” he says. “As a result, the project greatly improved my geospatial and statistical analysis skills and was instrumental my current graduate research in animal movement ecology.”

“Rus et al. provide an unusual demonstration of the interaction between migration experience and seasonal environments,” according to Oklahoma University’s Jeff Kelly, an expert on avian migration. “It is likely that the migration experience that older birds have enables them to extend their summer season through early spring and late autumn migration despite declining atmospheric conditions. Rus et al.’s demonstration of this insight into the interaction between age and the migratory environment expands our thinking about the life history tradeoffs that occur across the annual cycle of migrants.”

Baby Ospreys Now!

( , 5 march 2017)
Ospreys, fish-eating raptors, are breeding now on Sanibel, FL. This female is delivering fish to her partially grown young. She ate some of the fish herself first, starting with the head,  then she began to feed the babies, pulling off very small bits of fish.
The Osprey nestling period is 50-55 days. Ospreys can have from 1-4 young and eggs do not hatch at the same time. The first egg may hatch up to 5 days before the last one. The oldest hatchling dominates its siblings and may monopolize the food brought. If food is abundant food will be shared and all the chicks will survive. Ospreys breed in parts of the West and northern U.S and across Canada, and live all year in FL and parts of the Gulf Coast. You can see them migrating through much of the country.

Can we bring vultures back to Thailand?

(Authors: Dr. Boripat Siriaroonrat and Kaset Sutasha; Photo: Lip Kee; )

It’s the most dramatic bird decline ever recorded – faster even than those that robbed our planet of the Passenger Pigeon Ectopistes migratorius or the Dodo Raphus cucullatus. Since the 1990s, a staggering 99% of the vulture population in Asia have disappeared – a drop from several million to just a few thousand.

As a result of these steep declines, four species of Asian vulture – White-rumped Vulture Gyps bengalensis, Red-headed Vulture Sarcogyps calvus, Slender-billed Vulture Gyps tenuirostris and Indian Vulture Gyps indicus – are now assessed as being Critically Endangered – the highest threat category of all, and a status that indicates that if we do not continue to act, they will disappear from Asia’s skies within our lifetimes.

The main driver for the decline of vultures on the Indian subcontinent is well-publicised – the use of the veterinary drug Diclofenac to control pain and muscle fatigue in sick and aging cattle. Unfortunately, the drug proved lethal to vultures, who were unwittingly killed in large numbers in South Asia when they feasted on the poisoned carcasses of cattle who were left out in the open to die by herders.

Fortunately, the use of Diclofenac is now banned in India, Nepal and Pakistan, and thanks to the introduction of initiatives such as Safe Zones (areas in which threats are controlled within a 100kn radius, allowing viable populations to develop), vulture numbers are now finally stabilising on the Indian subcontinent. But why have vultures all but disappeared from other parts of Asia where Diclofenac isn’t an issue – as just as importantly, can we bring them back?

In Thailand, as in other parts of South-East Asia, Diclofenac isn’t an issue for vultures. Although the drug is widely available in pharmacies, it comes in cream and tablet forms, and is intended for human use – not for cattle. Despite this, the situation for vultures is even worse than it is in India – although two migratory species Cinereous Vulture Aegypius monachus and Himalayan Griffon Gyps himalayensis, can still be spotted every winter, all three of the species that were once resident in the country (Red-headed Vulture White-rumped Vulture and Slender-billed Vulture) are now extinct in Thailand.

Of the three, the Red-headed Vulture was the most abundant and could be found right in the center of Bangkok until the late 1960s-early 1970s, when burials were not widely practiced and dead bodies were left in the open waiting to be burned.  A cholera outbreak in Bangkok in the 19th Century is immortalised by sculptures of vultures feeding on corpses at the Golden Mountain (Wat Saket), which are still standing for us to see today even if the birds themselves are not. Vultures took advantage of the dead bodies until the modernization of the country in the 20th Century.  With cemeteries now becoming normal practice, vultures have struggled in the face of the reduced food availability

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The Raptor Situation in Costa Rica

white-hawk2.jpg
(Patrick O’Donnell, March 4, 2017)

What birder doesn’t get excited about raptors? Sort of like the mega birds, these aren’t your average worm-eating, seed-feeding, chirping guys with brightly colored plumage. Instead of being “little brown jobs”, most are large, in charge, and always ready to sink their talons into prey. By merit of their dimensions and fierce appearance, even non-birders throughout history have taken note of the raptors.

In Costa Rica, we have more than our fair share. In keeping with high diversity in other aspects of the avian kingdom, including falcons and excluding owls, this small country has a raptor list that tops fifty species. It’s a fine selection of birds for a place the same size as West Virginia but it also comes with a catch commonly found in tropical forest ecosystems. There might be a lot of species, but competition and other factors result in fewer individuals of each species. This basically means that it’s not easy being a raptor in Costa Rica. While there’s a lot of protected habitat, with so many other raptors and birds to compete with, each species has a pretty small population. In fact, because the numbers are so small, I bet we could get a fair estimate about the numbers of every raptor species in Costa Rica with a bit of effort.

To throw another monkey wrench into the raptor situation, clime change isn’t doing them any favors. The hotter, drier weather in Costa Rica might be helping the caracaras and a few other open country species, but the ones that rely on healthy humid forest environments are being seriously challenged. As with so many other bird species in Costa Rica that require humid tropical forest, various raptors seem to also be in decline. A few, like the Ornate Hawk-Eagle, are probably out-competing other species and thus on the increase but the numbers for most seem to be going down.

So, to make a long story short, it’s getting even harder to see raptors in Costa Rica and thus that much more pertinent to know about the best places for seeing them. In general, the best spots aren’t going to be wide open fields because those are recent, human-made habitats much more suited for cattle than forest birds. Instead, spend more time in protected areas with humid forest where you can see the sky and canopy. This way, you can spot that White Hawk making a bright exclamation point against the green wall of forest.

But don’t take my word for it, come to Costa Rica to check out the raptor situation for yourself. You’ll see a few hundred other bird species while looking for hawks, hawk-eagles, and kites anyways.

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