Fall Landbird Vagrants

Northern CA, 1994-99

Contents:

This page arose partly out of a wish to do something, however useless, with all the transcripts I've written up in the past five years. This past (1998) fall, the landbird migration seemed exceptional, but I was missing any historical context. A few old-timers I asked opined this was the best fall for rarities since the early 1980's. I don't have enough data to confirm that, but what I do have makes that sound reasonable.

Any and all comments are welcome. I've preemptively described below a bunch of reasons why the methodology is lame and the data too biased for any real scientific purpose, so you needn't point that out. I'm most interested (for now) in hearing how similar or dissimilar were the experiences of birders in other areas, especially Humboldt, SLO, LA, and San Diego counties in California, as well as Oregon, Washington, and Arizona.

Table 1: Doves to Warblers

Species

'94

'95

'96

'97

'98

'99

Average

White-winged Dove

2

2

2

4

1.7

Ruby-throated Hummingbird

1

0.2

Yellow-bellied Sapsucker

4

5

4

3

2

1

3.2

Red-naped Sapsucker

2

1

3

2

1.3

Yellow-bellied Flycatcher

Alder Flycatcher

1

0.2

Least Flycatcher

6

8

2

3

13

2

5.7

Gray Flycatcher

3

1

1

5

1.7

Cordilleran Flycatcher

1

0.2

Eastern Phoebe

2

1

1

1

2

4

1.8

Dusky-capped Flycatcher

1

0.2

Great-crested Flycatcher

Sulphur-bellied Flycatcher

1

1

1

0.5

Eastern Kingbird

3

3

6

2

5

1

3.3

Tropical Kingbird

15

15

12

12

16

10

13.3

Scissor-tailed Flycatcher

1

0.2

White-eyed Vireo

Yellow-throated Vireo

1

1

1

0.5

Plumbeous Vireo

2

5

4

1.8

Blue-headed Vireo

1

5

4

4

2.3

Philadelphia Vireo

1

1

2

5

5

2.3

Red-eyed Vireo

4

5

6

6

7

3

5.2

Yellow-green Vireo

1

2

2

2

3

1.7

Sedge Wren

Dusky Warbler

2

0.3

Northern Wheatear

2

1

0.5

Veery

Gray-cheeked Thrush

1

1

1

0.5

Gray Catbird

1

4

0.8

Sage Thrasher

3

6

3

1

4

3

3.3

Brown Thrasher

1

3

1

0.8

Black-backed Wagtail

1

1

0.3

BB/White Wagtail

1

0.2

Red-throated Pipit

2

9

3

2

2

3

3.5

Blue-winged Warbler

Golden-winged Warbler

1

0.2

Tennessee Warbler

18

20

8

6

19

28

16.5

Virginia's Warbler

2

6

5

2

1

4

3.3

Lucy's Warbler

1

3

1

4

1.5

Northern Parula

3

7

2

5

5

1

3.8

Chestnut-sided Warbler

21

15

6

10

37

58

24.5

Magnolia Warbler

15

14

2

7

23

17

13

Cape May Warbler

2

1

2

3

1.3

Black-throated Blue Warbler

7

5

5

3

23

7

8.3

Black-throated Green Warbler

1

2

6

1

1.7

Blackburnian Warbler

5

7

2

1

8

7

5

Yellow-throated Warbler

1

0.2

Pine Warbler

Prairie Warbler

3

3

7

10

9

12

7.3

Palm Warbler

64

63

25

29

42

49

45.3

Bay-breasted Warbler

1

1

1

1

3

1.2

Blackpoll Warbler

27

40

14

3

60

40

30.7

Black-and-white Warbler

17

23

10

11

27

15

17.2

American Redstart

31

46

30

12

44

33

32.7

Prothonotary Warbler

2

1

3

3

7

1

2.8

Worm-eating Warbler

2

0.3

Ovenbird

3

2

1

1

2

3

2

Northern Waterthrush

9

13

5

8

14

12

10.2

Louisiana Waterthrush

Kentucky Warbler

1

0.2

Connecticut Warbler

1

1

1

0.5

Mourning Warbler

1

1

1

2

0.8

Hooded Warbler

2

1

1

1

0.8

Canada Warbler

4

1

3

1

1.5

Painted Redstart

1

1(2?)

0.3

Table 2: Tanagers to Orioles

Species

'94

'95

'96

'97

'98

'99

Average

Summer Tanager

2

1

2

3

1.3

Scarlet Tanager

1

1

0.3

American Tree Sparrow

2

1

1

4

1.3

Clay-colored Sparrow

37

18

12

13

46

9

22.5

Brewer's Sparrow

7

6

10

8

7

8

7.7

Field Sparrow

Black-throated Sparrow

3

3

1

1.2

Lark Bunting

3

3

2

4

10

1

3.8

LeConte's Sparrow

Swamp Sparrow

31

23

7

8

12

11

15.3

White-throated Sparrow

25

35

10

11

49

9

23.2

Harris's Sparrow

2

0.3

Green-tailed Towhee

3

1

1

2

1.2

McCown's Longspur

1

2

2

0.8

Smith's Longspur

1

0.2

Chestnut-collared Longspur

9

14

11

10

9

3

9.3

Snow Bunting

1

1

1

0.5

Rose-breasted Grosbeak

7

8

6

7

10

8

7.7

Indigo Bunting

7

3

5

3

3

7

4.7

Painted Bunting

1

1

0.3

Dickcissel

1

0.2

Bobolink

14

11

3

3

7

1

6.5

Rusty Blackbird

3

1

1

0.8

Common Grackle

Orchard Oriole

2

5

6

3

6

2

4

Baltimore Oriole

1

2

3

1

1.2

Scott's Oriole

1

0.2

Summary

'94

'95

'96

'97

'98

'99

Average

Total species:

52

55

56

52

59

52

54.5 (81 total)

Total individuals:

438

478

265

242

599

405

404.3

Diversity:

3.270

3.333

3.528

3.531

3.426

Not calculated

3.513 (total)

Total "eastern" species:

40

43

41

36

46

40

41 (57 total)

Total "eastern" individuals

396

423

218

198

546

369

358.3

Total CBRC species:

6

10

11

5

9

9

8.3 (24 total)

Total CBRC individuals:

6

13

16

7

18

13

12.2

Common individuals:

286

298

134

115

352

262

235.2

Percentage of common:

65.6%

62.2%

51.0%

47.5%

58.8%

64.7%

58.0%

In the above tables, bolded species names denotes CBRC review species. (In truth, this is a mediocre indicator of rarity for this region, as the CBRC review list is based only on statewide status. For instance, Cordilleran Flycatcher is a regular breeder in NE California, but seems to be an exceptional rarity in this region; Scott's Oriole breeds in southern California, but is much rarer than Baltimore Oriole in this region; etc..)

Italicized names are "non-eastern". Deciding on what species qualify as "eastern" isn't always obvious. Great Basin species (e.g. Green-tailed Towhee), southwestern U.S and Mexican species, and Asian and Alaskan species are excluded, but some species have both southwestern and eastern races. In particular, I've assumed Summer Tanagers in our area are usually of the nominate eastern "rubra" race. Also, all Palm Warblers qualify, even though truely eastern "Yellow" Palm Warblers are rare.

What's fairly interesting is that the "non-eastern" component has been very steady, at about 45-55 individuals each year, far less variable in numbers than the eastern vagrants. Tropical Kingbird numbers, for instance, have been between 12 and 16 birds every year. What variation there is from year to year seems to be independent, i.e., good eastern years can be mediocre non-eastern years and vice versa. (In 1999, only a mere 36 "non-eastern" 36 birds came through.)

The common 10: The following species have been the most common over the past 5 years: Palm Warbler, American Redstart, Black-and-white Warbler, Blackpoll Warbler, Chestnut-sided Warbler, Tennessee Warbler, Clay-colored Sparrow, Swamp Sparrow, White-throated Sparrow, and Tropical Kingbird. This was used to generate yet another pointless statistic, in the hopes of elucidating whether "good" years were, relatively speaking, better for common or less common birds. The answer seems to be that proportionally more individuals fall into the "common vagrant" category in good years than bad. But, oddly, 1998 was marked by an intermediate percentage of common vagrants. Perhaps there was so much "good stuff" that birders tired of calling in these species. [You get roughly the same results if you consider the most common 10 eastern vagrants (subtract TRKI, add MAWA) as a percentage of overall eastern vagrants: 72.2%, 70.2%, 56.9%, 55.6%, and 66.1% for 1994-1998 respectively]

Diversity is measured using the usual -sum(pi* log( pi)) formula, and tells us absolutely nothing.

How good was 1998?

Pretty darn good. Numbers of the following species were far above average (as percentages of the average of the previous 4 years):

Some of the less regular vagrants, like Gray Catbird, Black-throated Green Warbler, Prothonotary Warbler, and Lark Bunting, were far more numerous this year than usual, some with more reports this fall than the previous four combined.

These numbers are exaggerated by how utterly awful 1996 and 1997 were (more individuals were seen in 1998 than both 1996 and 1997 combined!), but, by any measure, things were hoppin'. The turnaround in Blackpoll Warbler numbers from 1997 to 1998 is an amazing contrast: 3 versus 60! And while only a single Blackpoll was found in all of September 1997, at least 44 came through in September 1998.

Meanwhile, some of the more usual vagrants actually weren't reported in unusual numbers - Palm Warblers and Swamp Sparrows were well down from '94 and '95, and numbers of Tennessee Warblers and American Redstarts were just good, not great.

An oddity: Prairie Warbler numbers seem inversely related to the quality of migration. Explanations, anyone?

But 1995 was also pretty good...

Not only is 1995 the second best of these years, but a fire in October of '95 closed Point Reyes for weeks right in the middle of migration. Who knows what was out there! Then again, with Point Reyes closed, lots of birders went elsewhere and found other birds that might have been missed.

What about 1999?

The fall of '99 started off with a bang, and mid-September saw a stunning flurry of activity, but the hammer fell shortly after September 20th. Chestnut-sided Warblers and Tennessee Warblers were everywhere, and the two Mourning Warblers in this area were joined by another in Monterey County and two on the Farallones. Other species barely made their presence known, especially when compared with 1998:

Flycatchers were extremely scarce - only 18 vagrants, compared to 43 in 1999 (and 8 vs. 27 if you exclude Tropical Kingbird) - and only 2 Least Flycatchers, one Eastern Kingbird, and no Gray Flycatchers. What happened?

Dates included

I chose August 15 through November 30. The latter date is a bit late, as it includes a lot of wintering birds, and therefore jacks up Palm Warbler, Swamp Sparrow, and White-throated Sparrow counts, but it does match the end of the fall Field Notes reporting season. That season begins on August 1, but, in practice, landbird migration hasn't really started by then.

Species included

Basically, just passerines, plus a few others out of personal curiosity. Only vagrants are included. (Northern Shrike should be in the table, but was omitted the first time around, and I'm too lazy to add it back in). In practice, anything with less than about 50 reports per (average) fall makes for a decent cutoff.

Counties included

The above tables do not include all reports called into the BirdBox. In general, I eliminated all reports from Northeastern California (e.g. Siskiyou, Lassen, Modoc), and all reports from the Sierras and east (esp. Mono). Including these counties could greatly skew counts of some birds that are vagrants to the coast.

In addition, I've excluded Kern, Monterey, Humboldt, and Del Norte counties. In each case, these counties are only infrequently called into the BirdBox. Kern County is universally considered part of Southern California, and Monterey, Humboldt, and Del Norte rely on their own alerts, and only rarely call the BirdBox. Given the cutoff at Monterey, San Luis Obispo and San Benito are also out. I should have excluded Santa Cruz, since that county generally relies on Monterey's RBA, but I didn't. Too late now.

The Central Valley is included, though, in the end, a large majority of the reports came from the coastal counties of San Mateo, San Francisco, Marin, Sonoma, and Mendocino. For what it's worth, I've included westernmost Placer County (i.e. the Brewer Road longspurs), but none of the Sierra regions of that (or any other) county.

Finally, I've deleted all reports from the Farallones. These islands fall in San Francisco County for administrative (and list-keeping) purposes, and have some incredible reports, but birders can't visit these islands. So, they're off. My statistics, my rules.

I've gotten comments from birders in some of these excluded counties that might be of interest. Don Roberson wrote in about Monterey county: "Fall 98 [was] an exceptional year for Blackpolls (best since back in the 1970's, I think) and some other eastern vagrants... However, fall 1996 was also pretty good here". Matt Heindel wrote, "For Kern, it was one of the best years on record, though just average for warblers," and especially good for rarities.

I'm extremely interested to know if any Humboldt, SoCal, or even Oregon and Washington people can provide any similar comparisons. Was 1998 that good in your part of the world? Were 1996 and 1997 that bad?

How duplicates are eliminated

Poorly.

In general, the same species seen on consecutive days in the same spot would always be considered the same individual (except for obvious age/sex differences). However, beyond this simple and naive rule, it gets much harder. Places aren't visited every day, not all observers call in birds each day, and skulkers go without showing themselves despite the most ardent efforts. Even worse, birds can fly. (No, really, they can.) We know birds move from one ranch to another on Point Reyes, and more conspicuous birds can be refound at entirely different spots - witness the Painted Redstart in 1998, first found in the Marin Headlands, then at the Point Reyes Lighthouse, then at the Nunes Ranch, and finally at the Fish Docks on Point Reyes, all over a period of five days. Likely the same bird, but then again, maybe not.

Added up, this probably inflates the totals from migrant hot spots, and deflates the totals from more local spots. Whether it affects the relative standing of year-to-year totals is questionable.

How incorrect ID's are eliminated

Even more poorly.

Completely bizarre and unsubstantiated reports are eliminated. However, no attempt has been made to go back and check on acceptance of any CBRC birds, or to find out whether any individual reports were submitted and passed muster with the regional Field Notes editor. Reports called in as "possible" so-and-so's are not included, but "probables" are usually included, especially if relevant field marks were described at the time, and the birds aren't truly exceptional. I'll probably end up offending someone by omitting their sighting, but, remember, my opinions don't actually matter.

Such low standards are, I feel, essential if I want to be able to compare this year's sightings (none of which, obviously, have been reviewed yet) with past years, which is the whole reason I did this. At least that's my excuse, and I'm sticking by it.

Other reasons why this data is useless

Recent splits: Solitary Vireo and Northern Oriole were only split recently, and the recent rise in Baltimore Oriole and Plumbeous and Blue-headed Vireo reports is unmistakable. Even when those races were being identified pre-split, it's likely that they weren't being called in. It's also possible that, post-split, overeager birders anxious to increase their state or county lists will misidentify these races, . Look for this to happen again if Fox Sparrow or Sage Sparrow are split.

Patagonia rest stop effect: good birds lead to more good birds. Witness the barrage of rarities at the Fort Funston Skyline Grove in '98.

Varying effort of birders: The notion that lots of birds are around leads to more general effort, which leads to more birds, etc. On the other, other hand, the more genuine rarities are around, the fewer second-rate rarities might get called in.

Last updated December 4, 1999. Send comments, etc. to Adam Winer. The contents of this page are free for any use whatsoever, with no need for permission, though I can't imagine any real reason for wanting to do so.