Monday, May 12, 2008
All Three Riverside Eyasses Believed Dead
Intrepid foremel of the Riverside nest stuck tight as the branch swung and swayed.
11:13PM The Riverside Tiercel arrived at the nest with a rat.
Blog Contributor Eleanor Taubor writes that she was told by long time Hawkwatcher and photographer Rik Davis that on Friday, May 9th, he visited the Riverside nest, and only saw two eyasses. He wondered at the time if perhaps there had been a mistake in the count as he never sighted a third. It never appeared. It's unclear whether Rik visited before or after the rain so there may have been something wrong with at least one eyass while the other two were still acting reasonably normally.
On Saturday, May 10th, Lincoln Karim and Bruce Yolton reported no observations of eyasses on the nest plus erratic behavior on the part of the adults.
On Sunday, May 11th, Cal Vornberger reports seeing the formel, Intrepid, remove a dead eyass from the nest and carry it to the lawn. Lincoln will take the body to New York State Wildlife Pathologist Ward Stone on Monday for a necropsy.
What went wrong?
Dr. Stone will no doubt tell us eventually but in the meantime I can't help but wonder why three thriving young Red-tails have seemingly died. My first thoughts were Frounce or rat poison. I then learned there had been a drenching rain and cold temperatures on Friday which could also be a death sentence
How old were these eyasses anyway? I started to investigate. When we actually see them above the nest rim or we see feeding behavior, that isn't necessarily the day they've hatched. There are fewer experienced Hawkwatching eyes at Riverside daily, than there are at the Hawk Bench so in particular we may have caught this hatch late.
I looked back at my field notes and as of March 11th, Intrepid was sitting half down in the nest and therefore had probably started her clutch. If we add 28-34 days for a hatch we come up with eyasses out of eggs from April 8-12 approximately. Fledging occurs about 6 weeks after hatching, so these three might have been ready to go in a week or two.
Of course all the previous data is deductive, none of us know positively when the eggs were laid and the first day they hatched.
What went wrong? So far I've come up with three possibilities: Disease, Poison, Cold.
I mentioned the disease Frounce. It is a bacterial disease that is contracted by raptors from infected pigeons. Contrary to what some say, that "pigeons are carriers but aren't affected by the disease" that is untrue. Malnourished pigeon's health is impacted by the disease but it is just called by a different name.
When the no feed ban was put into effect in the parks, the increase in disease and the decrease of prey had me worried. Not only that pigeons depend on humans for food in the city, they are feral domesticated animals and therefore the ban was inhumane (By the way, from the NYC Board of Health, there are absolutely no documented cases of humans getting disease from pigeons. Yup, you heard it here folks.) but also that an unhealthy prey population or a nearly nonexistent one, could wipe out the urban raptors.
I've collected the Hawk Eats data. The park Red-tails eat about 81% pigeons, 9% squirrels, 8% rats and the rest tend toward the out of the ordinary, songbird, gull, nestling, etc. It does vary by season, year, territory, and time of day.
Poison as in rat poison could be another culprit. True we're told that the parks use a rat bait that is less toxic to raptors, but Riverside is a very narrow park and the Riverside nest is quite close to buildings in which the old style less expensive bait, the anti-coagulant kind, may well be used. Rats poisoned by this bait absolutely do come out in the daytime in a desperate search for water. I've seen them many times in my neighborhood, in Grand Central, and Penn Station. I've seen rats brought to the Riverside nest before dusk when most self respecting rats are still hiding out somewhere. True many poisoned rats do crawl off to die, but many also go into the open to search for water. But, a caveat here, not all daytime rats are poisoned as sometimes a colony may be disrupted by construction, flushed out of their holes, and conceivably into the park to be nabbed by raptors.
The third possible culprit is cold drenching rain and resulting hypothermia. According to research that was done early in the 20th century in Alaska, cold drenching rain is a leading cause of nest failure. The formel gets soaked, the eggs or downy eyasses get cold and bam, they get hypothermia and die. I thought that only eggs and very young eyasses would be affected but I may have gotten the wrong impression and even fully feathered youngsters are at risk. If it were hypothermia, I assume the eyasses would go nearly at the same time. Whereas the other causes might have a more staggered mortality, but nothing is set in concrete.
I know that nature is a very hard system and animals die everyday as do humans. But the beautiful young pair in Riverside, with their three lusty eyasses plus the fact that the formel looks so much like Tristan--and Pale Male before him, seemed a kind of consolation for the failure of the Fifth Avenue nest yet again. And yes we know that not every year can be a bumper crop of eyasses as last season seemed to be in so many places in the country including New York City. We know that if it happened every year, many eyasses would be hungry and there just wouldn't be enough room for them all.
Still no matter the good reasons that not all creatures may have a long life, including the ones fed to those eyasses, at every feeding I am glad the eyasses are fed, but I also grieve for the creatures who make up their dinner.