On 2/13/08 I headed down to Brawley for the Burrowing Owl Consortium meeting. There were a number of great talks, and I’ve included a synopsis at the end of this entry of what I found most interesting.
On the morning of 2/14, I spent an hour at Cattle Call Park before the meeting began. This Red-naped Sapsucker was partial to a small eucalyptus.
I was happy to find the reported Gray Flycatcher.
This calling Mourning Dove (note "inflated" neck) was interesting: a fair amount of iridescence on its neck and the odd sharp transition of the head and neck color with the rest of the body.
And the now-ubiquitous Eurasian Collared-Dove.
Northern Mockingbirds were so numerous…
they were trash birds.
On Saturday morning, 2/16/08, I joined the LeConte’s Thrasher/Algodones Dunes tour. It was a beautiful morning, somewhat marred by the noise of the ATVs on the south side of Hwy 78. We had nice, but somewhat distant, scope views of the thrasher singing and a five-mile walk through the dunes.
Desert primrose.
These darkling beetles were abundant. I’d like to go back just to photograph the cool patterns that their tracks make in the dunes.
An interesting moth.
The Burrowing Owl Consortium meeting was part of the Salton Sea International Birding Festival. There were a couple of excellent but depressing talks on the Salton Sea. Long story short: there will be less water going into the sea since there will be less water from the Colorado River for agriculture. If the sea’s level drops, it will become more concentrated with salt and other constituents, and eventually become a dead sea. There’s a $8+ billion plan to save part of the sea, but it has yet to be funded.
In the evening I was able to find the Neotropic Cormorant at Fig Lagoon–on the second try. I managed a few poor digiscopes.
Guy McCaskie drove up and told me he had just seen the Tropical Kingbird at the Rio Bend RV Park/Golf Course. With a little light left, I was able to find it.
Reports of a Crescent-chested Warbler (and recent reports of Aztec Thrush and Eared Quetzal) in Madera Canyon were too much to pass up–only another five hours.
I arrived at the upper parking area at Madera at 0615 on Sunday, with a Northern Pygmy-Owl calling. The trail was treacherous, with a slick icy middle and up to 10" of snow from two days earlier. The warbler wasn’t seen again after the snow. In fact, there were hardly any birds active in the upper canyon.
I was amazed to see three mountain spiny lizards out sunning on a rock surrounded by snow. It was still cool when they were out around 1130.
Down at Santa Rita Lodge, this Arizona Woodpecker was caching seeds from the feeder.
Farther down the canyon was this cooperative Townsend’s Warbler.
As well as this gorgeous Painted Redstart.
Preening.
I arrived in time to see the Northern Jacana at Casa Grande, AZ.
What a neat bird. It flew twice, showing its bright yellow underwings. It held its wings up for a few seconds before folding them.
Here it is with a Sonora mud turtle.
The ag lands south of Casa Grande reminded me a bit of the Imperial Valley, and, sure enough, I even saw a Burrowing Owl along with many round-tailed ground squirrels. There was also a lot of new development threatening the ag lands.
*******************************************************
From the Burrowing Owl Consortium meeting: of particular interest to me were the talks by Geoff Holroyd, Dave McDonald, and Courtney Conway. They built upon each other, and led to some very interesting conclusions (I apologize for over generalizing some of this material):
To paraphrase the most direct statement: there are no Burrowing Owl populations–the Western Burrowing Owl, from Canada to Mexico, California to the Dakotas, is ONE population. Various genetic markers show that there is continual gene flow between these populations. Adjacent local "populations" are no more closely related to one another than owls sampled thousands of miles away from one another. On a genetic tree, there is no geographical pattern, as one might expect. All Western Burrowing Owls sampled are quite closely related. If I’m remembering this one example correctly, samples from Lemoore, CA showed a closer affinity to birds from Colorado than they did from those sampled at Carrizo Plain, CA. By contrast, the Florida Burrowing Owl is quite genetically distinct from the Western Burrowing Owl, as would be suspected.
This all stems from the fact that Western BUOWs move around a lot. Birds may be "resident" one year and migratory the next. As might be expected, younger birds are more likely to disperse than older birds. Larger males are more likely to be resident than smaller males. In one study, a bird that was a migrant in one year has a 50% likelihood of being a resident the next year. A bird that is a resident one year has a 69% likelihood of being a resident the next (but a 31% likelihood of migrating).
Populations have been tracked by banding (still fairly low numbers), some radio telemetry, and with over 6,000 feather samples. Stable isotope analysis of feather samples shows where the bird was when it was growing the sampled feather (for basic info on stable isotope analysis, check http://biology.usgs.gov/cro/Information%20Sheets/StableIsotope.pdf).
One interesting example of how much these birds move around: a banded female was observed with young and a mate on 4/30 in Arizona. The same female was found that same year with 7 young and a mate (I assume a different one) on 7/12 in Canada!!!
So, what does all this mean? Well, everyone agreed that the population has been declining. This is based on reduction of habitat quality. However, instead of thinking of this as the extirpation of local populations, as many of us have (at least in part), it is rather a contraction of formerly occupied areas within the larger Western BUOW population.
I’m not sure I don’t still believe that there are some especially isolated areas where birds are holding on (think sites in the Bay Area) that, once the birds breeding there decline to an unsustainable level, it is unlikely for new birds to come in to replace them. I’m not sure how BUOWs find new sites, but they often turn up in odd places. Apparently suitable habitat is often unoccupied while drain pipes made available for a couple of days will attract an owl. It would be interesting to know how "random" these events are and how much scouting for new sites the owls are actually doing. When they are excluded from a burrow, for example, where do they go?
Below are some more interesting concepts, added mostly without comment from me:
Populations trends appear to show that Canada is losing some of its owls to the U.S. The birds are staying in the U.S. Site fidelity in Canada is low.
The Imperial Valley, CA and Sinaloa, Mexico pops appear to have grown where nearly all others areas have declined.
The overall range has contracted especially in the north (Canada) and the east (Dakotas, Texas, etc.).
Declines largest where owls are most strongly migratory. Pop trend generally south and west to heavy ag areas like Imperial Valley.
Canada pop has experienced a 22% decline each year in recent years, leading to an overall 95% decline.
Some birds that migrated south to Mexico were found under vegetation and not in burrows–some in heavily vegetated areas.
The reason owls line burrow entries and nest chambers with manure may be to attract insects, making feeding easier.
Human disturbance is probably attractive to owls. Levees, development attracts them until greater than half the land is built up–then numbers begin to drop.
2006-2007 Statewide survey: the official results will come out soon, but I wrote these down as fast as I could (so there may be an error or two).
1993 population estimate was 9266 breeding pairs.
2007 estimate is 8465 pairs in areas surveyed in 91-93, plus additional, previously unsampled portions of the state, leading to an overall population estimate of 9236 breeding pairs.
Many areas had owls in 91-93, with none or far fewer in 2006-2007. Especially true at more urban sites.
Main portion of population in Imperial Valley: 6400 pairs is the current estimate (521 were actually detected). ~6600 in 93.
Coachella Valley (0 in 93; 53 pairs in 06-07).
No owls were found at the Modoc Plateau, an area that hadn’t been covered in 91-93. Good numbers were found in the Palo Verde Valley near Blythe–another area not covered in 91-93.
The other stronghold is in the southern Central Valley: ~1100 pairs (~1400 in 93).
I wrote down a lot of the pair estimates for the regions, but probably should wait for the official survey results before promulgating them.
5 km X 5 km blocks were surveyed. These included blocks with previous owls records ("owl blocks") and random blocks. Estimates were based on a formula using owls found on randomly selected blocks (# of owls found in "owl blocks" and other sites discovered incidentally were simply added to the totals that were estimated using the random blocks). This was covered quickly, but I’m sure there will be more details on the methods in the upcoming report.
A couple notes on artificial burrows. There was a talk from Bob Fox from Wild at Heart of Arizona. They have done a lot of artificial burrow construction and have relocated owls to artificial burrows. Owls are kept at least 60 days (maybe it was 90?) and fed mice. Obviously very labor intensive. Not currently an option in CA.
They have also had many owls move into their sites. They build hundreds of burrows to give the owls a lot of options. In a conversation with them afterwards, they felt that our Bufferlands nest chambers weren’t buried deeply enough (which could explain why the owls have been using them more in the winter). They bury their chambers 4 feet. Dig with a backhoe.
In their experience as well as Jack Barclay’s in San Jose, they build a lot of burrows and don’t do much maintenance. The San Jose sites are on in the flat ground and mowed over the top. The desert sites in AZ don’t usually require mowing.
I brought up the fact (as others have) that the current practice of "passive" relocation (exclusion) is based on the premise that the owls will move to sites nearby, but there has been very little (if any) study of this. Where are the owls going? It’s also a major assumption that artificial burrows built for the owls that are excluded will be occupied by those owls. Then there are those built miles away (or years after the fact).
I also raised the problem that comes from levee projects or other temporary disturbances that require the owls to be excluded. Leads to driving all of the owls out of the area with no knowledge of where they are going.
All agreed that it is a major problem that so many of the owls (including most of the state pop in Imperial Valley) are living on levees or along water conveyance canals.
Friday and Saturday were the Salton Sea Bird Fest. Good but depressing talks on the problems with the Salton Sea. Reductions in allocations of Colorado River water may threaten (or reduce) ag in the Imperial Valley which could threaten (or reduce) the BUOWs.
Major problems for the Salton Sea. It is an amazing place harboring literally millions of birds. It has functioned as a replacement for the loss of the Colorado River delta (the river rarely reaches the Gulf of CA since there are so many urban and ag demands on it).
In the past, siltation in the delta would occasionally lead to the Salton Sink filling with Colorado River water. The latest example of this was an accident on the All American Canal in 1905. The Colorado River shifted into the canal, out of control, and filled the Sink. The levels have been maintained over the decades by ag runoff. This has allowed the Sea to persist, but has led to increasing concentrations of salts as the water evaporates and the salts, phosphates, and other constituents are left behind.
The water is saltier than the ocean. If nothing is done, it will become a dead sea. First, ALL of the fish will die. Eventually, all the inverts will die, and it will be of no value to birds or other wildlife. With cuts in water allocations (and, therefore, runoff to the Sea), this could happen as early as 2018. A huge plan has been proposed (52 miles of levees) to create a ring of better water along the outside of the current sea, with a dead zone in the middle. Also, with less water, there will be much exposed land. The strong winds will put more particulate in the area, leading to already bad air quality to become much worse. More at http://www.saltonsea.water.ca.gov/
To quote from 
