September 03, 2013
In Primorye, Russia, a research team headed by Jonathan Slaght with the WCS and the University of Minnesota, looked at 20,213 square kilometers of forest and found that owl nesting sites are usually within old, large trees – such as Japanese poplars, chosenia and cork bark elms. The nesting sites are all located along streams – which are also the habitat for the owl's primary food source, salmon. This means Blakiston's fish owl is entirely dependent on riparian forests, which refers to the banks along a water source or the interface between water and land.
A Blakiston’s fish owl in Primorye, Russia. Photograph © Jonathan Slaght, WCS Russia
An intact riparian forest doesn't just provide prime nesting site, but also enhances the owl's prey when large, old trees fall into the water. Researchers found that the presence of tree trunks in the water was strongly correlated with owl hunting. The scientists further suspected that this was related to salmon abundance as the added obstacles affect the "stream-channel complexity" - combining areas of slow-moving backwaters and fast moving channels to suit different life stages of the salmon. Some streams also had warm springs, which attract salmon during the winter months, providing a food source for the fish owls when it may otherwise be scarce.
However, the owl's habitat requirements make them extremely susceptible to extinction: the IUCN Red List currently classifies the species as Endangered. Not surprisingly, the logging industry represents one of the main threats to their numbers. Logging is a significant contributor to the local economy and, as such, is unlikely to be eliminated from the area, but the high levels of extraction are threatening the fish owl and many other species in the region. The loss of older trees, especially, limits the availability of fish owl nesting sites and decreases the amount of downed trees needed to create prime foraging areas. Roads for the logging industry are also posing another challenge.
Researcher Shurik Popov scales an old-growth Japanese poplar tree in Primorye, Russia, to inspect a Blakiston’s fish owl nest cavity 15 meters above the ground. Photograph © Jonathan Slaght, WCS Russia
The logging industry also uses many dead or dying trees to create temporary bridges to carry across commercial logs, essentially robbing the fish owls of nesting sites. In addition, logging roads cause erosion when built too close to the waterways, affecting the health of the stream and making it less suitable for salmon, which in turn hurts the giant owls.
Loss of habitat and food are not the only threat to this species. Jonathan Slaght said that the owls are also "vulnerable because they have an extremely low reproductive rate. In Russia, they only breed once every two years, and typically raise only one chick."
In comparison to most other bird species, a young Blakiston's fish owl will remain with its parents for over a year before heading out on its own and doesn’t reach sexual maturity until the age of three years old.
"It basically takes four years for a single bird to be added to the breeding population" says Slaght.
The owls are also very territorial and if a mate dies, it may be a long time before a new potential mate appears in the area.
"Even years before the surviving member of the pair breeds again… losing even one breeding owl is devastating to local populations," Slaght notes.
WCS is now working with the logging industry to alter forest management practices near rivers in a bid to preserve the fish owls. Jonathan Slaght also believes that a "great way to conserve fish owl numbers is to try to contain some of the salmon poaching that occurs, in order to keep prey numbers high for fish owls."
A female Blakiston’s fish owl flushes from its nest, a cavity in an old-growth Chosenia tree in Primorye, Russia. Photograph © Jonathan Slaght, WCS Russia
Tracks in the snow in Primorye, Russia, reveal that a Blakiston’s fish owl hunted here the night before. Photograph © Jonathan Slaght, WCS Russia
Muddy runoff from a logging road built too close to a tributary of the Maksimovka River in Primorye, Russia, degrades habitat for salmon and, by extension, Blakiston’s fish owls. Photograph © Jonathan Slaght, WCS Russia
Slaght, J.C., S.G. Surmach, and R.J. Gutiérrez. 2013. Riparian old-growth forests provide critical nesting and foraging habitat for Blakiston’s fish owl Bubo blakistoni in Russia. Oryx 47: doi: 10.1017/S0030605312000956
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(05/28/2013) The Russian Far East is one of the wildest places on Earth: where giant tigers roam snow-covered forests and the world's biggest owls stalk frozen rivers. Bordering northern China and North Korea, the forests of Primorye are known for the diversity of habitats, including coastal forests along the Sea of Japan, vast coniferous forests in the Sikhote-Alin mountains, and even steppe. These diverse ecosystems also makes the forests a hotspot for endangered species, including Amur tigers (Panthera tigris altaica), Blakiston's fish owls (Bubo blakistoni), and one of the world's rarest big cats, Amur leopards (Panthera pardus orientalis), which number only 30-50 animals.
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