|Posted by Brian on May 5, 2017 at 2:15 AM|
As of last Saturday, sampling in California has concluded for this year. I’ll be working along the southern Oregon coast for the next few weeks, I might head to central Oregon in the Florence area (where the hybrid zone ends, and pure Rufous Hummingbird populations begin), and end the field season. The weather has gotten a lot better; less rain, more sun, and highs in the high 50s, which sometimes feels like a heat wave. I saw my first bear of the season last week at Del Norte Coast Redwoods State Park in California; one of the few black bear that actually had black fur that I’ve seen.
Where I’m at now presents the largest unknown of the transect. The Siskiyou mountain range rises to about 6,000 feet in elevation really close to the coast, potentially keeping Rufous Hummingbirds from interbreeding or interfering with potentially pure Allen’s populations. However, thus far, the populations seem to be just as intermediate as the one in Crescent City, northern California. There seem to be two possibilities, which will (hopefully) be sorted out in the coming weeks: the hybrid zone is disjunct, meaning there is a transition from a Rufous-like to an Allen’s-like phenotype (a summary of overall physical characteristics) from Florence, Oregon, to Port Orford, Oregon, a stretch of about 40-50 miles where no hybrids (and possibly pure Allen’s) are found due to the presence of the Siskiyou mountains, and a recurrence of hybrids in northern California where that mountain range is no longer present. The other possibility is that the hybrid zone forms a fairly smooth cline, where there is an overall transition from a Rufous-like to an Allen’s-like phenotype from Florence, OR, straight to the Eureka, CA, area. As of now, the latter seems most likely. One thing is certain; the populations are sparse (or at least less accessible) in this area compared to anywhere else I’ve worked.
After a couple weeks of field work in my first year, two months of field work last year, and nearly three months of field work this year, I’ll have sampled over 200 birds. Over the course of my dissertation, I will probably have sampled in the neighborhood of 400 birds. Why so many? First off, the hybrid zone is a lot larger than any of us anticipated, and sample size will thus need to increase. Also, using a technique called admixture mapping, we’re going to try to find the genes responsible for the pendulum display in Allen’s Hummingbird using recombination that takes place in the hybrid zone. If you have pure Allen’s and pure Rufous interbreed, a hybrid’s genome will include the genetic makeup of both species. Because of this, only bits and pieces of the phenotypes expressed by a “pure parent” might be present, as is the case with the pendulum display. So, we’re looking to correlate the genomes of hybrid birds with the different elements of the pendulum display they perform, and determine how it might have evolved.
Sometimes territorial male hummingbirds I’m getting courtship data from will visit feeders as often as every five minutes. Hummingbirds feed about 14 times an hour because of their extremely high metabolic rates, so some of these guys are getting most of the nectar in their diet from my feeders! When a hummingbird consumes nectar, it fills its crop, which is a storage space for food in birds. Often an individual will perch somewhere for a short while following feeding. This is so the crop can empty and digest the food into its system. Once the crop is about half full, the bird will go feed again. When a bird doesn’t go to a feeder, it can seem impossible to catch it. That’s where mist nets can be useful. A few weeks ago, we built a mist net that has been working out well in catching target birds that won’t visit the feeders. When a bird flies into a mist net, it gets tangled in the net and is typically stuck until safely removed by somebody (with no harm done to the bird). Lots of pictures and videos to share when things start slowing down, including a video of myself and the lab tech at UCR (David) catching a bird using such a net.