January Surveys Done...Whew.

Burrowing owl, Solano Co, January 2010.........ZS

We barely completed the January raptor surveys this year, thanks to the incredible amount of rain that fell in the last half of the month. All data are in and I've presented the species densities across all routes as they compare with the previous two seasons' data (see table below, numbers represent birds/100Ha or birds/sq.km.). Notable stats include the continued dearth of Rough-legged hawks and robust Red-tail, kestrel, shrike and harrier numbers.

Species	January
	Y1	Y2	Y3
Turkey vulture	0.21	0.22	0.31
Osprey	0.00	0.00	0.00
White-tailed kite	0.05	0.05	0.05
Bald eagle	0.02	0.02	0.03
Northern harrier	0.11	0.08	0.14
Sharp-shinned hawk	0.00	0.00	0.00
Cooper's hawk	0.01	0.00	0.01
Red-shouldered hawk	0.02	0.04	0.05
Swainson's hawk	0.01	0.00	0.00
Red-tailed hawk	0.65	0.66	0.80
Ferruginous hawk	0.06	0.06	0.05
Rough-legged hawk	0.02	0.01	0.00
Golden eagle	0.01	0.01	0.01
American kestrel	0.28	0.30	0.38
Merlin	0.01	0.01	0.01
Peregrine falcon	0.00	0.00	0.01
Prairie falcon	0.02	0.03	0.02
Great-horned owl	0.00	0.00	0.01
Burrowing owl	0.01	0.02	0.02
Short-eared owl	0.00	0.00	0.00
Loggerhead shrike	0.06	0.09	0.13

Raptor densities, January, Year 1-Year 3

December routes completed

Taiga Merlin, Yolo County. 4 Jan 2010..............................ZS

Nearly all the data from the December surveys have been compiled. Observers again worked hard to complete their routes in a timely, yet productive fashion during the holiday season. The monthly total for all raptors observed on all routes combined will likely be around 2500 (compared to 2147 in Year 2 and 2414 in Year 1). Overall raptor density (birds/100Ha) is around 2.2 bp100Ha, which is up from both Years 1 and 2 (2.0 and 1.8, respectively). These figures represent average densities per survey route. Once we correlate the raptor and habitat datasets, we can calculate the density by habitat type...a much more important figure.

Comparison of December species densities (by route), Years 1-3

Some notable items this season include the lack of Rough-legged hawks (only one was observed in December), an apparent boom in Loggerhead shrikes (nearly double the previous year's density), and the apparent consistency of Ferruginous hawks and Prairie falcons. Kestrel numbers are notably higher than in previous years, which is encouraging, but not terribly meaningful with only three years of data. Observers also witnessed the near-death of a Golden eagle on a power pole after it was attacked by a Red-tailed hawk and was nearly electrocuted as it struggled to free a stuck talon. Scary moments.

We are looking forward to the rest of the winter season and many cool raptors to count and enjoy.

Dark Red-tails, Habitat

Dark/Rufous Red-tailed hawk, Butte Co. 11/09. ZS

Dark morph Red-tailed hawks immigrate to the Central Valley each winter in decent numbers. Many of these birds show typical plumage, but a few are unusual. The bird in the above photo is slightly odd due to the white streaking/flecking on the breast, which is a Harlan's Red-tailed trait. The tail was typical for a calurus adult. This bird nearly fits the description in The Wheeler Guide of dark calurus x dark harlani (western x Harlan's). There is debate over whether or not harlani and calurus intergrade in Alaska and northern British Columbia. Is this bird a possible intergrade or simply an aberrant dark/rufous morph calurus? I, for one, am not sure.

We are about 2/3 of the way through ground-truthing the survey routes for changes in habitat. While the changes along the routes are not terribly drastic, they are happening. We have seen new vineyards and orchards as well as alfalfa switching to row crop and vice versa. This year we have been noting stretches of road that are free of telephone poles and/or fencelines, to see how these potential raptor perches might affect observed densities along routes.

Dark Rough-legged hawk, Solano Co. 2/08............................ZS

Winter birds trickling into CV

Over the past couple of days, we have been receiving a huge dose of northerly winds and cooler temps here in the Central Valley. I am hoping in its wake we'll see an increase in numbers of ferruginous hawks, prairie falcons and perhaps a first rough-legged hawk of the season.

I did pick up a light ferruginous hawk on Monday at Robinson Rd. in Solano County, a full month and a half after my first one of the season. And today I spotted a Prairie falcon cutting a low arc in the wind north of the Jepson Prairie. With these birds and the gradual swelling of Red-tailed hawks and kestrels in the valley, it is beginning to look a bit like winter around here.

And to end this post, an ID shot taken on Robinson Road.

Robinson Rd, Solano County. 26 October 09 ZS

New Survey Season Approaching

We are on the cusp of the third winter season for the survey. The weather is changing (tempestuous rain here in Davis today...fantastic!). The birds are changing...lots of white and golden-crowned sparrows, yellowrumps, kinglets and waterfowl on the rise. I had my first ferruginous hawk of the season on September 8 in southern Solano County. That bird was almost a month early according to past Central Valley records. Yesterday, I went looking for mountain plovers (no luck) but the usual spot is along the Jepson raptor route. The shrike numbers were impressive, so I wonder if their numbers will be strong on the surveys. This route typically records the highest shrike count for the survey.

I should have a summary of the first two years of the project up here soon in PDF.

Sac/San Joaquin Valley Comparison

Merlin, Solano County...........................ZS

Wow, I can't wait to get through the process of cleaning up our data. When we ground-truthed the habitat earlier in November, there were numerous changes that needed to be made to the Year 1 habitat data. In addition, we are proofing the raptor data so that birds are placed in the correct habitat blocks. It's hard to explain, but it's a time-consuming and headache-induciing process. I've been sick recently, which has made computer work more of a chore than it already is.

The Central Valley is composed of two smaller, named valleys: the Sacramento Valley (SV) in the north and the San Joaquin Valley (SJV) in the south. While not technically separate valleys, these regions are named and defined by the major rivers flowing through them. They meet at the Delta west of Stockton. This is a convenient geographical division across which I will present a simple comparison.

Twelve of our survey routes lie in the SV north of the Delta and 8 lie to the south in the SJV. I computed the average bp100Ha for each route (all species lumped) and for both years. The densities tend to be higher in the SV, while certain routes in the SJV had high densities. Note that the average density in the SJV barely reached the level recorded in the SV (January in Year 1). Also note how densities along certain routes remain very consistent (i.e. Yuba, Beale, Jepson, Linden) while there was some degree of fluctuation in others. While there were some increases in apparent density along some routes, there was an overall decrease in density in both regions from Year 1 to Year 2.

Raptor Densites in the Sacramento Valley by Route

Raptor Densities in the San Joaquin Valley by Route

Year 2 Survey Effort

Juvenile Golden eagle.....................................ZS

Below is our survey effort for Year 2 of the survey. I've presented the person-hours for each route, kilometers per route as well as the total number of surveys done on each route. The standard was to do three surveys throughout the winter, but some folks chose to do extra ones, which was fine. It gives us more data that can make the habitat association facet of the project stronger. For analyses where comparisons between routes are necessary, we will only use one survey per month for each route.


The next table is a comparison between Years 1 and 2 of the average density of each species (birds/100Ha) by month. This metric is a way to normalize the data so that numbers can be compared across routes. This density figure was calculated for all species on each route as well. Numbers for most species are remarkably similar between the years.