In case you hadn't seen Peter Pyle's writeup on distinguishing Sagebrush and (canescens) Bell's Sparrows in fresh plumage (fall/early winter; the primary period when their ranges will be overlapping), you can find it here. What is particularly useful is that the writeup contains photos of study specimens from Berkeley's Museum of Vertebrate Zoology; most of these photo sets are comparing fresh plumage, but a few are of worn plumage.
Definitive Prebasic Molt (according to the Sage Sparrow Birds of North America (BNA) account) begins in June, finishing by mid-September (whether anyone has looked at timing differences etc by subspecies, I don't know). Records of arrivals of Sagebrush Sparrows onto territories range from late February to late April. In Mono County, canescens begins nest building in early March, and the final nests started in mid-late June. Southern populations of canescens may start up earlier (I haven't seen any data on it) but I suspect will at least skew to the early side of that range. At any rate, you can see that there will be worn Sagebrush Sparrows migrating northward through canescens territories!
As a note to make things more interesting for us all, the BNA account notes that migrating flocks of "Sage Sparrows" have been found containing both (canescens) Bell's Sparrows and Sagebrush Sparrows.
Hope you find it useful, too!
Sunday, September 8, 2013
Friday, September 6, 2013
|Vermilion Flycatcher female on nest in screwbean mesquite|
|Another area search plot, Sandy Valley|
|Here's one of 3 maps that I filled in during a single visit of my area search plot|
At the end of the survey, we’ll end up with a map of all of our bird locations, criss-crossed with lines – solid ones indicating the movements of a particular individual, dashed lines indicate that we had different individuals, along with a few scribbled behavioral notes. The day’s not done yet, though! We’ll transfer each species’ locations, lines and notes to a species-specific map, that will eventually encompass all of the data for that species from all of the visits. Before each visit, we’ll scrutinize those maps, and figure out where the territory boundaries are unclear and where we need to spend some more time. Then, at the end of our 8 to 10 visits, we’ll draw our territory boundaries, and summarize our findings.
|If you squint, you can make out letters marking locations: the first visit is A, the 2nd visit, B, and so on.|
The area searches are useful for a lot of purposes – they give us detailed natural history information, and because they provide such detailed location information, they’re excellent at monitoring changes in habitat and bird communities through time, so they’re incredibly useful to monitor habitat restoration projects. Plus we’re able to use them to do some calibrating of our extensive program of point count surveys – by conducting point counts on the area search plots, we’re able to compare what our point count surveyors record to the mapped territories, which helps us determine detection rates.
You don’t need UTM grids and GPS units to do your own territory mapping, though. Find your favorite park on (for example) google maps, switch to satellite view, zoom in, and print it out. With a pencil and your binoculars, you’re now set to map out territories of the bird community – or just a species or two of interest. When you’ve mapped out a territory, take a look at it - what does it tell you about that species’ habitat/structural needs? Where is the nest located relative to the territory boundary? If a pair renests, with either a replacement clutch or a second brood, do their territory boundaries shift? As they move along in breeding stages, how do their movements change? Do their defended areas contract, or expand? And of course, spot mapping doesn’t have to be limited to the breeding season, you can also see how birds’ uses of various habitats changes across the seasons. All fun things you can explore with mapping!