A story in the latest online edition of the Berkeley Daily Planet reminds us of the dangers of the stuff we use without thinking to rid ourselves of pests.
Joe Eaton writes that someone in Berkeley trying to rid themselves of rats has caused the death of esnl‘s favorite flying critter, the Cooper’s Hawk:
It’s the worst kind of déjà vu. Last month a juvenile Cooper’s hawk was found dead in a pool of blood on a west Berkeley sidewalk, not far from where three other hawks succumbed four years ago. This year’s victim tested positive for the anticoagulant rodenticide brodifacoum, with a trace amount of another rodenticide, diphacinone. Brodifacoum was also implicated in at least two of the 2007 deaths.
Some rodenticide users, homeowners and professionals alike, seem oblivious to the collateral damage the stuff can cause. Even if the bait is placed indoors, a poisoned rat or mouse can wander outside where it can be picked off or scavenged by a predator or pet. Although Cooper’s hawks are primarily bird-hunters, rats may be “starter” prey for younger individuals, easier to catch than pigeons or starlings. Hard-pressed parents may also bring rodents home for their hungry nestlings.
Death by brodifacoum is particularly nasty. It kills by internal bleeding, which results in intense thirst. (The 2008 hawks were found in a backyard wading pool.) Like other “second-generation anticoagulants,” brodifacoum was introduced in the 1970s after rodents developed resistance to older products. The risk of secondary poisoning of non-target species like hawks is increased by the fact that the poison is not immediately fatal: a rat may keep coming back to the bait for several days as the brodifacoum in its body builds up to several times the lethal amount.
According to the American Bird Conservancy (www.abcbirds.org/abcprograms/policy/toxins/pesticide), brodifacoum has killed hundreds of birds of prey: red-tailed and Cooper’s hawks, great horned owls, eastern screech-owls, golden eagles. Even mountain lions and endangered kit foxes have fallen victim. In New Zealand, populations of both raptors and insect-eating birds decreased following a brodifacoum-baiting program.
The second chemical found in the hawks’ tissues, diphacinone, is one of the first-generation anticoagulants. Previous tests on mallard ducks and bobwhite quail had been used to claim that it was only minimally harmful to birds. However, a more recent US Geological Survey study found that small amounts of diphacinone were lethal to American kestrels. As little as 3 grams of liver from a poisoned rodent could kill one of these small falcons.
Read the rest.
First, some Cooper’s Hawk factoids, thanks to Cornell University’s All About Birds page on the critter. Lots of interesting things thing, including recordings of the critter’s call.
To the ornithologically minded, the hawk is known by its formal handle, Accipiter cooperii.
Some other hawk lore:
- A Cooper’s Hawk captures a bird with its feet and kills it by repeated squeezing. Falcons tend to kill their prey by biting it, but Cooper’s Hawks hold their catch away from the body until it dies. They’ve even been known to drown their prey, holding a bird underwater until it stopped moving.
- Once thought averse to towns and cities, Cooper’s Hawks are now fairly common urban and suburban birds. Some studies show their numbers are actually higher in towns than in their natural habitat, forests. Cities provide plenty of Rock Pigeon and Mourning Dove prey. Though one study in Arizona found a downside to the high-dove diet: Cooper’s Hawk nestlings suffered from a parasitic disease they acquired from eating dove meat.
- Life is tricky for male Cooper’s Hawks. As in most hawks, males are significantly smaller than their mates. The danger is that female Cooper’s Hawks specialize in eating medium-sized birds. Males tend to be submissive to females and to listen out for reassuring call notes the females make when they’re willing to be approached. Males build the nest, then provide nearly all the food to females and young over the next 90 days before the young fledge.
- The oldest known Cooper’s Hawk was 20 years, 4 months old.
This afternoon, one of the hawks lit in a favorite perch two trees west of its nesting tree. The branches are thinner, making it easy to catch a glimpse of possible prey. This fellow was in the midst of grooming when a pigeon passed by, and the lens snapped at the instant he [?] turned to catch a glimpse of possible prey. But an ongoing itch proved the more compelling draw, so at least one Rock Dove [the true name of our pretend pigeons] was able to escape the raptor hug of death — at least for the moment.
Seconds later, another avian arrived, this one a sibling. The bird perched higher up the tree in one of the few areas heavily shaded by the branches above.
11 July 2010, 600mm, 1/1250 sec, f5.3
All three of the young birds were perched a couple of trees south of the nest, but two had flown by the time the camera was in range, leaving this critter as the sole candidate for today’s hawk post.
10 July 2010, 600mm, 1/500 sec, f6.3
Chin-scratching is quite a feat for a young Cooper’s Hawk, since it requires standing on one foot while keeping balance from atop a branch.
8 July 2010, 600mm, 1/500 sec, f5.3
A pair of the young were ought to catch the rays today.
8 July 2010, 440mm, 1/1000 sec, f5.6
Here a sibling comes in for a landing, just a bit too fast for the camera to grab the sharpest possible image. Still. . .
8 July 2010, 440mm, 1/800 sec, f6.3
While a nestmate dines on birdie de jour, a sibling looks on hungrily moments after being driven off with by the well fed erstwhile comrade.
3 July 2010, 600mm,
At least esnl was. Shooting a bird flying with a long lens is tricky, but this worked out perfectly. One of the young taking wing. . .
6 July 2010, 600mm, 1/8000 sec, f5.6