The Rusty Blackbird Blitz—Year 3

Posted by Russ Greenberg on April 15, 2011

Rusty blackbirds were tracked down and reported from throughout eastern North America for the third straight year, increasing our knowledge of their winter distribution. The Rusty Blackbird Blitz covered a two-week span (January 31 through February 14) when birders continue to locate the remaining hot spots for wintering rusty blackbirds and report the information to E-bird.

I greatly appreciate everyone's efforts, from the muddy boots birders to the state coordinators and steering committee participants. The data from the three years show some consistent patterns in the overall flock sizes and the geographic distribution of large rusty blackbird flocks. The three years differed in the number of very large flocks (more than 500 birds), with none being reported this Blitz season. Many more insights to come.

Participation

211 birders submitted reports under the E-bird Rusty Blackbird Blitz protocol. This is slightly more than last year and over 20 percent more from the first year.

These observers filed 214 reports where at least one rusty was observed (eliminating duplicate reports from the same site) totaling 9,495 birds. This is a decrease from the last year's 11,736.

An average of 45 birds per sighting was up from last year's 37, but below 77 reported from 2009.

Number of birds per sighting in each year

Bar chart
Average number of birds per sighting: 77, 37, and 45 in 2009, 2010, 2011

State Total Lists (including zeros)

Distribution

Rusty blackbirds were reported from 27 states (27 and 31 in previous years) primarily from east of the 100th Meridian (one report from Montana).

In declining order of number of sightings, the following states had 10 or more sightings:

The number of states with 10 or more sightings (8) declined from 15 in 2010 and 12 in 2009. All of the states in the top tier based on the number of reports are within the core southern wintering range.

Median

2010 median count by state
Median count by state

Relative Abundance per Site – a comparison of states

StateNMeanMedian
South Carolina6128200
Alabama16124196
Mississippi10118145
Indiana275120
Texas295222
North Carolina144453
Connecticut44483
Georgia214365
Pennsylvania73758
Florida63685
Maryland53255
Virginia142649
Kentucky22640
Arkansas72236
New Jersey42235
Tennessee182122
Louisiana201917
Missouri51315
Illinois11212
Ohio4912
New York2712
Oklahoma558
Michigan234
West Virginia334
North Dakota234
Kansas434
Montana111
Total2144548

Note that the mean and median are both presented, but overall the correlation between the two is high (r = 0.96) indicating that the mean is not skewed and therefore highly influenced by a few large flocks.

Rusty Blackbird Hotspots

Sixteen states had reports of 50 or more rusty blackbirds at a site. The leaders are all southern states including:

As in previous years, large flocks were relatively rare. The largest flock reported this year was 500, which is down from the previous two years when flocks of 2,000 or more were seen.

As in previous year, the largest flocks (over 150 birds) were concentrated between 32-36°N. (see map at bottom of page)

The Blitz versus general E-bird reporting

One interesting observation is that while the number of official reports for the Blitz had only shown marginal increases over the three years, the total number of rusty blackbird reports to E-Bird during January and February has sky-rocketed. The total was only about 400 in 2008 (the year before the Blitz began). This number increased to 700 in 2009 and increased to nearly 2000 in 2011.

I am not sure what the rate of growth of E-bird participation has been, but a five-fold increase in four years in rusty reports seems very high. I wonder how much of this is a collateral benefit from the publicity for Rusties surrounding the Blitz. The good news is that we should be able to use the total E-Bird data set for searching for "hotspots."

Further Analyses

There are much more data and many more analyses to conduct. My initial take is that the number of reports or the success rate (reports with rusties/total number of reports) will not provide much meaningful data. The former is a function of effort and the latter appears to be affected by the inconsistency of people filing null reports. It appears that the valuable data will be in group size and composition and local abundance. Since the purpose of the Hotspots Blitz was to locate concentrations of birds, this should not be too surprising.

We will now sit down with the complete three year survey and look more rigorously at the "hotspots" to see where they are and what landscape characteristic distinguishes these sites from not so good rusty blackbird locations.

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