McChord AFB & Morse, Period 6: June 26 & 28, 2011
by Dan Froehlich
- 26 Jun: Daniel Froehlich, Clarice Clark, Emma White & John White (driver)
- 28 Jun: Daniel Froehlich, Don Norman (driver), Emma White
We were blessed with two more days of perfect banding weather, not too cool at night so hardly any dew on the grass under the nets followed by persistent clouds during the day that kept the sun off the nets.
Here’s a summary of the captures at both stations this period:
26 Jun at Morse Preserve:
- Rufous Hummingbird 4 including 3 juveniles
- Western Wood-Pewee 1
- Pacific Wren 4 juveniles
- Bewick’s Wren 1
- Bushtit 2 juvies and 1 adult
- Red-breasted Nuthatch 1 second-year male
- Hutton’s Vireo 1 female originally banded in 2009
- Cedar Waxwing 1 female without any red waxy tips
- American Robin 1 juvie
- Swainson’s Thrush 2
- Orange-crowned Warbler 2
- Spotted Towhee 5 including 3 juvies
- Song Sparrow 1
- Black-headed Grosbeak 1 ASY female
- Western Tanager 1 bright SY male
- Brown-headed Cowbird 1 SY female
28 Jun at McChord AFB:
- Rufous Hummingbird 5 including 2 juveniles
- Willow Flycatcher 2 second-years
- Bewick’s Wren 1
- Chestnut-backed Chickadee 1
- Black-capped Chickadee 1
- American Robin 1 juvie
- Swainson’s Thrush 11!
- Orange-crowned Warbler 3 including 1 juvie
- Yellow Warbler 6
- Common Yellowthroat 3 including 1 juvie
- MacGillivray’s Warbler 1 ASY male
- Song Sparrow 7 including 4 juvies
- Oregon Junco 1
- Black-headed Grosbeak 2, a pair of ASY birds
Since I was at both MAPS stations this period, I looked at the recapture results from both sites. At McChord, 14 of the 45 birds were recaptures, while at Morse the relationship was 7 of 30 birds, so proportionally slightly fewer at Morse. What’s striking, though, is that of those 7 recaptures at Morse, all but one were of birds caught earlier this year, at one of the two previous banding sessions. Only the Hutton’s Vireo was from a previous year, a long-term resident originally captured as an adult in 2009. By contrast, a majority of the recaptures at McChord were birds captured in previous years. Among the 7 Swainson’s recaptures, for example, three were first caught earlier this year (one twice on the 28th), while the other three were recaptures of birds initially caught in 2008, 2009 and 2010. One of the Song Sparrows was first caught in 2006 as an AHY, so he’s an old-timer!
If this observation among the recaptures represents a pattern, it suggests that the bird population at Morse has pretty high turnover from year-to-year, while that at McChord includes more birds returning year after year. An analysis I did for Swainson’s Thrushes at the two stations a few years ago showed the same pattern: high within-year recapture rates at Morse vs. high between-year recapture rates for McChord. I’ll try to post that analysis on the website later this summer. What I found interesting about that result was that the Swainson’s were clearly breeding at both sites: lots of singing and feeding observations, lots of captures with full-blown brood patches and occasionally even nests. At McChord, the local breeders would hit the nets a few times a season, but chances were that recaptures later in the season hadn’t been caught earlier that season. But at Morse, we’d catch the same local breeders all season long, over and over again. Why? Was it something about the habitat?
To check it out, I pulled up satellite photos of the two banding sites:
The aerial view suggested an obvious answer. The Morse woodlot is a small island in a matrix of rural clearings; the McChord site is part of a large connected network of suitable Swainson’s Thrush woodlands. So the territory-holders at Morse cover the same ground over and over again, stuck within the confines of the reserve, hitting the nets scattered throughout repeatedly. At McChord, by contrast, the territory-holders move around larger patches hitting the nets only occasionally. It follows that the area sampled by the nets at McChord likely intersects more territories than at Morse.
The landscape perspective explains the many within-season recaptures at Morse, but it doesn’t address why the birds are more likely to return year after year at McChord. I guess it could be survivorship—perhaps survival is reduced when your breeding site is so constrained. Or could it be that birds at Morse move on after trying it there for a year? One of the MAPS assumptions is that at least within species, site fidelity—the likelihood an individual bird will return to its territory year after year—is fairly constant within age classes. But maybe the returns at these sites, just a few miles apart and with somewhat similar vegetation communities, suggest that individual birds adjust their site-faithfulness behavior based on the quality of their territories in the habitat matrix. It’s a hard idea to test because you’d have to show rule out alternative explanations. Another possibility, for example, is that the frequent netting during the breeding season at Morse induces them to move on! At least that resident Hutton’s Vireo wasn’t discouraged.
Emma White from Shoreline is PSBO’s high school intern for the summer; she’ll be attending our banding sessions regularly and helping out with keeping our data sheets in order. We’re excited to have her participate. She’ll also be blogging about the MAPS banding, so watch for her byline shortly.