Date: 6/13/18 10:51 am From: DJ Lauten and KACastelein <deweysage...> Subject: [obol] Re: Oystercatchers
A few comments on Wayne's comments:
On 6/13/2018 9:10 AM, Wayne Hoffman wrote: > > Second Point. Re release at Crater Lake. In the early 1970s there > were no known (or at least acknowledged-there was lots of paranoia > about falconers) active nests in Oregon. The first one found was at > Crater Lake, about 1977. This was a natural nest, apparently not the > result of hacking birds. It is a mistake to think that "There is > obviously no food supply in the national park." Peregrines can and do > subsist on land birds as well as aquatic ones. I have extensive prey > data from the Yaquina Head nestings, and at this site they eat more > land birds than aquatic ones. The bulk of the land bird prey are > Starlings and Eurasian Collared Doves, but they have also brought in > thrushes, an occasional Band-tailed Pigeon, a Western Tanager, a few > Crows, etc., as well as a Short-tailed or immature Long-tailed Weasel, > and several chipmunks and smaller rodents. I have seen reference > elsewhere to Peregrines that fed extensively on Gray Jays.
I know a falconer who probably knows more about Peregrine Falcons then anyone in Oregon. They are actually rather common even in forested habitat, and we have discussed what their food source would be in such habitats, and he is rather convinced that there are plenty of Band-tailed Pigeons, jays, and other species to sustain the populations. Peregrines do not dine on just shorebirds, as Wayne has noted.
> > Third point: Lars wrote "...none of them the result of human > effort—just spontaneous response to the opportunity. That is to say, > the expensive efforts bore no results." Indeed in some parts of the > country, urban-hacked birds seem to only be producing progeny that > nest in urban situations, and not re-populating historic cliff sites. > In Oregon not all hacking was in urban areas, and hacked birds did > contribute to the current population. I say this because I have > photographed many Peregrines to study plumage and other physical > characteristics, and I see far more evidence of mixed parentage than I > would expect if the hacking programs did not contribute to the population.
What is happening with Aplomado Falcons is not the same as Peregrines, and the hacking efforts of Peregrines around the country was definitely successful in helping to recover the species. Each case is unique.
> > > I realize that this is the same kind of evidence I cited for the > Oystercatchers - "surplus" nonbreeding adults suggest a healthy > population - but I think it is a reliable indication of > more-than-adequate recruitment to balance adult mortality.
A healthy population of Peregrines does not translate into a negative effect on any particular species population. In order for Peregrines to have that much effect on any population, they would have to be depredating more individuals than the population is producing. This would be a stunning phenomenon for any native predator on any prey species. Just based on the prey species Wayne has documented Peregrines bringing in pretty much suggests that they are not doing that.
With that said, it is important to understand that Black Oystercatchers are inherently a rare bird, and have never been all that common. The facts are that they inhabit a very narrow and limited band on habitat. They are not found a few hundred yards inland from the coast, nor are they found out at sea. They are only found from California to Alaska, and there are a limited number of available rocky islands for them to breed on, and thus by the nature of their habitat they are effectively limited to a certain population size. If Peregrines were limiting their population size, there certainly would not be "extra" adults in the population without mates or territories. There are diminishing returns for any Peregrine solely or mostly hunting on Black Oystercatchers - there simple are not enough of them to sustain a pair of Peregrines. This is all the reality of population dynamics, and predator prey interactions. It really is nothing to be overly concerned about.
Nature has a wonderful way of balancing itself.
Cheers Dave Lauten
> > Wayne >> >> On 6/13/2018 5:57:29 AM, Lars Per Norgren <larspernorgren...> >> wrote: >> >> * >> >> At one point I heard that there were three pairs nesting inside the >> city limits of Portland, none of them the result of human effort—just >> spontaneous response to the opportunity. That is to say, the >> expensive efforts bore no results. A fortune has been spent in south >> Texas to reintroduce Aplomado Falcons. Great Horned Owls eat them as >> fast as they are released. Money would be far better spent on >> chainsaws and their operators to remove the mesquite that harbors the >> owls, compromises the grassland. Not nearly as glamorous, but I like >> a bang for my endangered species buck. These high profile black holes >> pale in comparison to the Steller’s Eider. A graduate student working >> on their recovery program on Alaska’s North Slope told me it has been >> the most expensive program per bird to date. Two years ago 360 >> fertile eggs intended for cross fostering were never placed in nests. >> I met a biologist at Thompson Reservoir in June of 1982, when >> the Peregrine hacking program was in its infancy. At that time the >> first site planned for Oregon was Crater Lake. There is obviously no >> food supply in the national park, putative parents would have had to >> commute to Klamath Forest marsh. But there were many human visitors >> to the desert cliffs of Crater Lake, making it a high profile >> endeavor. lpn >>> On Jun 12, 2018, at 5:05 PM, Jeff Gilligan <jeffgilligan10...> >>> <mailto:<jeffgilligan10...>> wrote: >>> >>> >>>> On Jun 12, 2018, at 5:02 PM, Roy Lowe <roy.loweiii...> >>>> <mailto:<roy.loweiii...>> wrote: >>>> >>>> I don’t think peregrines have been hacked in Oregon for more than >>>> two decades. They’re doing well on their own. >>>> >>>> Roy >>>> >>> >>> They were being hacked on Sauvie's Island as recently s a few years >>> ago, as well as somewhere on the Washington side of the Columbia >>> nearby. I agree that they are doing fine on their own. >>> >>> Jeff Gilligan >>> >>