Wildlife Wednesday: peregrine falcons use ‘false alarm’ attacks to tire out prey

Plus: 3,000 illegal shark fins seized by the DFO, Atlantic Canada’s seals under investigation, salmon use ‘cooling stations’ to de-stress, and 16-kilogram tortoise found wandering spinach patch

Photo: Mosharaf Hossain/Flickr
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Capable of diving at speeds of up to 300 kilometres per hour, the peregrine falcon is the fastest animal on the planet. And according to new research out of Simon Fraser University in B.C., these birds are as fast in thought as they are in flight.

Long theorized but hard to prove in practice, the Wolf-Mangel model suggests that prey must prioritize safety over food foraging when they feel the threatening presence of a predator. As a result, predators could use false attacks to tactically tire out prey or force them to take bigger risks, then strike when they are most vulnerable.

Scientists observing peregrine falcons have now found evidence that these cunning raptors purposefully take advantage of this prey behaviour by using low-cost false attacks to advertise their presence to Pacific dunlins in Boundary Bay, B.C. 

By doing so, the dunlins are forced to flock over the ocean (where they are safe from predation but unable to forage) before high tide (peregrine falcons’ preferred time for hunting), expending energy and tiring themselves out. Then, when it comes time for the falcons to hunt for real, the dunlins lack the energy to flock off shore and the peregrines hunt with increased success — essentially gaming the system.

Shark fin coup

Canadian fishery officers along with US Coast Guard locate illegally possessed shark fins during an inspection in the North Pacific. (Photo: Fisheries and Oceans Canada)
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Approximately 3,000 illegal shark fins have been seized, along with a myriad of reported widespread fishery violations by Operation North Pacific Guard. For two months, the multinational mission, which was led by Canada, involved ocean patrols, air surveillance and satellites to find illegal high-seas driftnets, illegal fishing activity and examine fishing vessels.

Inspecting more than 400 fishing vessels, the mission patrolled approximately 12,000 nautical miles, ensuring the searched vessels complied with the conservation measures throughout the North Pacific. During this time, 58 violations were detected, as well as incidents of marine pollution, thousands of illegal shark fins (some of which were from threatened species like oceanic whitetip sharks) and many other violations.

In previous years, the annual mission has been led by the United States. It is instrumental in enforcing the United Nations Ban on High Seas Driftnets and ensuring vessels comply with regulations that protect against unreported fishing.  


A seal’s dinner

(Photo: Bouke ten Cate/Wikimedia Commons)
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The Sable Island grey seal herd off Nova Scotia is the largest in the world, a huge chunk of the 310,000-strong Scotian Shelf population. Harp seals, found primarily off Newfoundland and Labrador, number over 7.4 million. Together, these blubber-lined Atlantic Coast sea mammals are the subject of a new federal government investigation into the effect they’re having on the ecosystem following their boom after cod stocks collapsed.

When cod numbers dropped, the species they preyed on — capelin, herring and sand lance — jumped in numbers. Suddenly with an abundance of high-quality forage fish to feed on, seal numbers boomed exponentially. Sara Iverson and Suzanne Budge, biology and chemistry professors respectively at Dalhousie University in Nova Scotia, received $150,000 in government funding to study seal blubber and analyze their diet. 

They will make use of a new technique pioneered by Iverson that analyzes the types and amounts of fatty acids from prey in grey seal blubber to identify exactly what species they’re eating. 

Cold comfort

Close up of the cold thermal plume, in both visible light and thermal images. (Photo: Kathryn Smith)
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As if wild Atlantic salmon didn’t already have enough to deal with — from hungry bears to human-made dams — on their journey upstream to spawn. Now a new challenge has emerged: rising water temperatures in Nova Scotian rivers, a consequence of climate warming, is adding to the stress of a species accustomed to the cold ocean (the migration typically occurs in the summer, when river temperatures peak). 

Known as thermal refuges, natural groundwater springs and cold tributaries in rivers provide salmon with some relief, creating cold areas where the fish can stop for a while to cool down and de-stress. These “cooling stations” could mean the difference between life or death.

The Nova Scotia Salmon Association, along with Dalhousie University in Halifax, has spent four years mapping these crucial thermal refuges, which are becoming increasingly rare. They also launched a pilot project to create additional cold spots along the salmon’s routes, pumping cold water into key spots and digging underground trenches to redirect the meander of a river underground so the water would cool away from the sun’s rays before re-entering the river. 

Underwater wildlife cameras revealed that salmon congregated in both these engineered thermal refuges. The plan now is to scale up these pilot interventions.

Shell shock

Adrian Walton of Dewdney Animal Hospital poses next to Frank the Tank, a 16 kilogram sulcata tortoise. (Photo courtesy Adrian Walton)
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A spinach farmer expects to find the odd rabbit pilfering his crop, but a 16-kilogram tortoise was a bit of a shock. Nicknamed Frank the Tank, the juvenile sulcata tortoise was found happily wandering among rows of spinach and bok choy in Surrey, B.C, last week. He’s now at a local animal shelter and will be put up for adoption once he gets a clean bill of health.

Sulcata tortoises originate in Africa and it is illegal to bring one into Canada without an import permit. That said, now Frank is here, a local vet noted that he would make a great pet — given the right owners and space. He will likely grow up to four times as large and live for up to 150 years so any owner would need a succession plan.  

As well, these tortoises love to dig so his new owner would need to reinforce the walls of an indoor winter enclosure and provide an enclosed field or paddock for him to hang out in — and dig to his heart’s content — during the summer months.  


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