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Mexitron
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Doesn't seem likely, but perhaps a lack of the vultures prefered nesting sights contributes to their scarcity as well.
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Pescador
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Skipjack is right, I live just south of San Lucas Cove and we also have a ton of birds on the shore but I have yet to see a buzzard on San Marcos
Island or Tortuga for that matter where I spend a lot of time. I will question the locals to get their take on this. I know they could fly there if
they were so inclined but for some reason they must opt to not do that. On San Marcos Island their are full time residents on the gypsum mine and
they also have a dump which should attract these birds but I can not remember ever having seen them. I will have to get a pitcher of bloody marys and
do some serious scientific study on this.
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Graham
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Thanks Pescador and Skip. That San Marcos Island observation is really interesting. Unless San Marcos is overun with feral cats from the settlement
out there, I may have to amend the cat theory.
I like your approach to scientific study. Let us know the results.
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Skipjack Joe
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Graham,
The reasons I don't think it's feral cats is because:
1. there are lots of cats around the developed areas on the peninsula and the birds seem to be fine.
2. there are other birds on the island and they seem to survive with the cats.
3. there should be cliffs and ledges where birds should be safe from cats.
If food is not the limiting factor then perhaps they do have difficulty soaring over open water. I thought that perhaps they need those warm updrafts
to soar. They like to follow the cliffs along the shoreline very often. But I could swear remembering laying on my boat in open water and seeing them
far above, a dot in the sky. You would think that crossing 5 miles of open water would be simple.
Competition? I've never seen frigatebirds molest them. They really occupy different niches.
I still think it's lack of sufficient carrion. In a natural setting these birds need a lot of territory to support them. Perhaps the carrion isn't in
the right state for them to eat. Maybe gutted fish and animals are just right but others are not. Perhaps they prefer freshly killed animals and won't
touch partially decomposed matter. Perhaps they only eat fish because anglers have done all the work and warm blooded animals is what they would eat
under 'natural' situations. They definitely have some preferences. I've never seen them eat the dying squid we find everywhere. Need to understand
their feeding habits better before making any judgements. There's probably stuff on the internet ....
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bajalera
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I think they're scared off by the lady vampire wearing the white dress, the one who usually walks the backroads at night.
Nice buzzard essay, Jorge.
\"Very few things happen at the right time, and the rest never happen at all. The conscientious historian will correct these defects.\" -
Mark Twain
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Roberto
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| Quote: | Originally posted by Graham
There used to be a huge scallop camp on the island with as many as 1500 residents, at a time when LA Bay had a fraction of that population.
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I believe there was also a fish camp just off the north end of the island, on Isla Mejia. No permanent settlement in modern times that I know of.
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Pescador
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This is really interesting, because I do not think it has anything to do with food. At San Marcos Island there is a dump which is a typical Mexican
dump with lots of food available but no one that I have talked to so far ever remembers seeing a buzzard there. I think it may have to do with the
issue of flying over water. In fact, now I am curious as to whether or not they fly to the closer islands within a mile of shore.
Now, Skipjack may be right about the soaring behavior over water and it is easy for our larger brains to understand soaring distance, but the
buzzard must not have a flight computer which lets it know it could reach the islands and has come to stay on shore.
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Graham
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Roberto, I think you are right on both points.
Certainly there was no permanent settlement on Guardian Angel Island. The scallop camp that I was referring to operated in the early 1970s. It was in
the SE corner of the island just above Isla Estanque.
At its peak, there were over 200 pangas operating. It was more like a village or small town with several stores, families were living out there,
keeping pigs and goats. You could get much better food and produce on the island than you could get at LA Bay at the time.
An enormous amount of trash was produced, including fish and scallop remains. At first it was all dumped in the sea, but that didn't please the divers
as it attracted a lot of sharks to the area where many of them had to spend hours underwater performing more controlled ascents after brushes with
decompression sickness. So a truck was brought to the island and most of the refuse was trucked to inland dump sites.
And Pescador you are definitely providing food for thought.
I have witnessed gulls mobbing and driving vultures to the water if they come too close to their nesting areas. In fact, I tried to rescue a vulture
in the water off an island in Bahia Concepcion. It was being attacked by several gulls and was close to drowning. I got it up on my sit-on-top kayak,
but the persistent gulls knocked it off again and eventually drowned it. As I paddled around I found several other turkey vultures dead in the water,
perhaps having met a similar fate.
Being over water near a gull nesting site is clearly a dangerous place to be if you're a vulture.
Thanks, Graham
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Skipjack Joe
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gulls and vultures as competing scavengers
| Quote: | Originally posted by Graham
I have witnessed gulls mobbing and driving vultures to the water if they come too close to their nesting areas. |
This made me think about the role gulls play in the whole thing but from a different perspective. If you drive along the highway north of the
immigration booth at GN and you encounter a road kill (cow, coyot, rabbit) you will invariably find vultures feeding on it. This despite the fact that
you're a half mile from the pacific. If you drive the half mile to the waters edge and find a dead spotted bay bass or corvina it will be the gulls
pecking at it. If you drive south to the fish cleaning stations at SLC you will see both vultures and gulls eating the fish that's tossed at them. In
the absence of man I think gulls are superior competitors for seafood than vultures.
Now lets consider an island in the cortez. Here there is an abundance of seafood right next to shore. The gulls become even more concentrated to the
point of nesting. They effectively greatly diminish the vultures ability to feed on what the sea delivers. So their effective feeding territory
becomes the island interior.
To me, the fact that vultures soar is a big deal. It means that in it's natural state the bird requires a lot of territory to sustain it. It glides
because it just doesn't get enough food to actively beat those wings in pursuit of a meal. It's a weak competitor. It gets by on whats left over after
everyone else is through.
It needs a certain amount of territory to sustain it and if the shoreline is removed from the islands then perhaps the remainder is not enough to
support a thriving population.
If that's the case then not all islands are alike. La Guardia should come closer to having the resources than say, La Raza, with it's huge gull
population and no inland foraging territory.
Food for thought. Although the picture is getting clearer in my mind.
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windgrrl
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..saw absolutely scads of turkey vultures near Los Barriles mid-Jan.
When the way comes to an end, then change. Having changed, you pass through.
~ I-Ching
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Crusoe
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Skipjack.......Good work. I think you have pretty much nailed it.Bird behavior is very fascinating stuff. Also in my travels I have observed that some
birds such as crows and ravens absolutley do not like saltwater.This could be why you never see turkey vultures totaly immersed in saltwater and
diving and feeding like ospreys and eagles. A bird bioligist I knew once compared them to chickens and roosters. They sure are fun to watch soar.++C++
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mtgoat666
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| Quote: | Originally posted by Graham
Where were the turkey vultures???
Anyway, there are not many places in Baja where you won’t see a vulture in two months. In my new book I took a wild guess as to why this might be so,
but I’d appreciate any insight or suggestions… |
Educated guess,... vultures are predators to eggs and bird chicks, and vultures are are probably driven from the island by the birds that nest on the
island, gulls perhaps.
Feral cats on the island sound like an ecological nightmare, but may be keeping rats in check, which rats would be an equally bad ecological disaster
if not kept in check by feral cats. Cats and rats have probably driven a few bird species from the island.
Every species has its niche -- and mans activities do a fine job of tweaking everybody's niches.
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Graham
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Wonderful feedback. Thanks Skip, Mtgoat, and Crusoe for all the great information and suggestions. I'm heading to LA Bay for a week or two... with a
very open mind.
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Pescador
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Well, I was wrong, there are turkey vultures on San Marcos Island. I was over there today and went to the windward side and definately saw at least 4
or 5. I had not seen them on the one side of the island, but they were on the east side and the wind was blowing from the east so it made some good
ridge soaring for them.
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