Last night I camped in a beautiful location near Naturita, Colorado. A Common Poorwill was singing me to sleep.

This morning's transect was pretty nice before the rain came. I had a handful of Sage Sparrows, Vesper Sparrows, Brewer's Sparrows, Chipping Sparrows, Lark Sparrows, Spotted Towhees, Ash-throated Flycatchers, Gray Flycatchers, and Say's Phoebes.

The rain started to come down pretty hard around the middle of my transect, so I headed back, hoping to avoid slippery roads. The traction wasn't too bad on my 7 mile drive out, and the rental Kia handled pretty well. It's continued to rain since I left, and I'm assuming the roads are impassable now.

Rainy, rainy, rainy. The Naturita library doesn't open until 10:00, so I'm wasting time, bumming internet off the visitor center (which is also closed; I'm sitting in the parking lot on my laptop).

I guess this is more of a listserv post, but oh well. Life is grand and I enjoy being a field tech.

Carl

A recent post on the Idaho listserv of a Ferruginous Hawk made me think to write this entry. A quiz photo of a juvenile light-morph Ferruginous Hawk was posted and the possibility of it being a Krider's Red-tailed Hawk was discussed. A common ID problem....I think I even show the two side-by-side in "Hawks From Every Angle".

I won't go into detail on how to separate the 2 (I posted a short response on the site), I just wanted to post 3 Krider's Red-tailed Hawks here showing how pale and lightly marked underneath they can be (adults on left and center, juvenile molting on right. Bird on right by Brian Sullivan.

It's funny how birders will drive 6 hours to see a rare bird in St. George, but that same rare bird could be located 6 hours away over a state line & few would care :).

Well, the field season has started, and I'll be doing surveys in western Colorado this year. I can promise you all entertaining stories from up and down the Western Slope, but I can't promise you any good Utah bird sightings this summer :(.

I hope that is okay with everyone, and I hope you all don't vote to kick me off the blog as I'll no longer primarily be a "Utah Birder." I promise to write a lot in the field, and I'll share with you whenever I'm home.

So far I've found that Colorado has just as many lions, rattlesnakes, coyotes and scorpions. They have more Sage Sparrows and Palm Warblers & less Snowy Plovers and Arches. Should be a fun season.

Carl

Base Reflectivity basically corresponds to the amount of radiation that is scattered or reflected back to the radar by whatever targets are located in the radar beam at a given location. These targets can be hydrometeors (snow, rain drops, hail, cloud drops or ice particles) or other targets (dust, smoke, birds, airplanes, insects).

The colors on the Base Reflectivity product correspond to the intensity of the radiation that was received by the radar antenna from a given location.

So how does this translate into numbers that make sense?

Other targets and hydrometeors show up in the same spectrum of reflectivity as one another. However, one key difference is the intensity at which they show up. To the left you can see the full spectrum of dBZ from -30 to 80.

Next to that are numbers for hydrometeors which show the actual millimeters per hour of precipitation in relation to the reflectivity.

To the right of that are the estimated number of birds per kilometer cubed. As you can see the non precipitation reflectivity is much lower on the scale and only go up to about 35 dBZ. Occasionally it does go higher, but that is rare.

In both scales, the higher the dBZ the higher the corresponding numbers are. So the more intense the weather, the more water that falls. The more intense the migration reflectivity, the higher the number of individual birds migrating.

In the radar images above, you can see the dBZ differences between the birds on the left, and the weather on the right. The radar image on the left is an example of a very nice night of migration around 25 dBZ in the center (the green area). This was taken on May 3 at around 10pm mountain time over the Oklahoma/Nebraska state line.

In my next post I will talk about why the radar image appears in a Donut shape, and about the velocity of the migrants.