Sunday, September 8, 2013

Sagebrush and Bell's (canescens) Sparrows

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!

Friday, September 6, 2013

Territory Mapping

Vermilion Flycatcher female on nest in screwbean mesquite
I’ve had some folks ask me about territory mapping, so I thought I’d share a bit about how the Nevada Bird Count does it (the Lower Colorado River project does it slightly differently in order to meet their particular program goals – minor variations on the same theme!).   Territory mapping (we’ll often also refer to it as area searching or spot-mapping) is my personal favorite way to get acquainted with birds of a new region or habitat, and is a fantastic way to learn the natural history of bird and plant communities.  Nothing beats point count transects for the chance to hike and explore and get a wide breadth of understanding of your birds and habitat, and their variation across the landscape – but the area searches are a great way to get depth.  Our plots are of variable size – basically, we want a plot to be big enough that we’re able to have it covered by 9:30-ish in the morning, but small enough that we’re able to have it covered well, and aren’t glossing over sections to get them done on time.  Not surprisingly, therefore, our Mojave Scrub plots are going to be a larger size than our coniferous forest or riparian plots – the former have a lot less habitat structure and fewer birds, so we’re able to cover more ground.  A 300 x 300m plot is fairly typical in streamside vegetation, where there’s a lot of structure.  We visit each plot 8-10 times; often our Mojave Scrub or sagebrush plots are able to be thoroughly mapped within 8 visits, but those extra 2 visits can make a big difference in our more complex plots!

Another area search plot, Sandy Valley
Basically, our surveyors are given an aerial photo overlain with a UTM grid, and on each visit, they will walk through the plot in a different pattern, making sure that they get within 50m of every part of the plot on each walk-through.  The different routes ensure that each part of the plot will get surveyed during the best part of the birding morning on at least one occasion, so we don’t have one location that is always surveyed at 5:30 a.m. and one location always surveyed at 9.  We walk through the plot, looking at and listening to birds, watching their behavior, and marking down their locations on our aerial photo.  Once we’ve finished our initial walk-through, somewhere between 9 and 10am, then we’ll often head back to a perplexing area to spend some more time watching, listening, and mapping.   The 2 biggest things to remember are (1) following individuals and (2) simultaneous detections.  When we find an individual, it’s useful to spend some time with it, marking down the path of that individual’s movement, particularly if it’s a singing male or is exhibiting other territorial behavior.   Do we see any behavior indicating where the nest might be found?  Concurrently, you want to look and listen to determine whether you have any other individuals of that species, and if so, map them too.

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! 

Happy birding,
- Jen