Dear Birders,

There seems to be general agreement that the 1999 spring migration
was one of the latest in recent years, especially for songbirds, and
especially for those that normally arrive in the month of May. In my
area, I would estimate that the peak migration was 7 to 10 days later
than normal for the majority of passerine species. This is correlated
with a spring which was unusually cool and stormy over much of the
Pacific Northwest.
I decided to try to test this hypothesis of late arrival on a
table of first arrival dates for the Nicola Valley in south-central
B.C. The results were not what I expected, but I thought they were
worth sharing with you anyway.
The table of 1999 arrival dates, versus average arrival dates,
with associated calculations, is in the attached Excel spreadsheet. I
apologize to those of you who don't have Excel and may not be able to
read the attachment.
First, a little background. The Nicola watershed, centred around
the city of Merritt in south-central B.C., is an area of about 7300
km2 (2800 square miles). Altitudes range from about 700 feet to 7000
feet. There is a wide variety of habitats including extensive
grasslands, forests ranging from ponderosa pine to Engelmann
spruce/subalpine fir, three large lakes (Nicola, Douglas, and Stump),
one large wetland (Guichon Flats), and many smaller lakes and
wetlands. I tried to spend a minimum of 8 to 15 hours birding in the
valley each week, and visit most major habitats, although I was not
able to visit all habitat types every week. About 80% of the arrival
dates are from my notes, but they are supplemented by some earlier
dates from Katharine Shewchuk (Merritt), Rick Howie (Kamloops), and
Jerry Herzig (Princeton), who I thank for making their notes
available. Nevertheless, this is mainly a single-observer compilation.
The table lists arrival dates for 114 species in 1999. There are
15 additional species with the notation "WINT"; these are species
which normally do not stay all winter in the valley, but which did in
1998/99 because of the unusually mild winter. This resulted in Nicola
Lake remaining unfrozen all winter, in contrast to the usual situation
where it is frozen from early January through early to mid-March.
A few species (e.g. Brown Creeper, Cassin's Finch, Lincoln's
Sparrow) have their 1999 arrival dates in parentheses, because they
almost certainly arrived 2 weeks or more before my first sighting.
Dates for these species were not used in the comparisons.
The "average" arrival dates are given in the next column, followed
by the number of years' records on which it is based (usually 3 to 5
years). This is not a lot of years' data, but it is enough to give a
fairly good idea of average arrival dates for all except the scarcer
or more irregular species.
The next column gives my earliest-ever arrival date for each
species for the Nicola Valley. Note that for 31 species, my earliest
arrival ever was in 1999. Several of these were "ties", but for a few
species, my 1999 arrival date was up to 2 or 3 weeks ahead of normal.
I probably spent a bit more time in the field this spring than in
previous years, but in general, the time expended was about the same
as in 1995, 1996, and 1997. I was absent from the area in spring 1998.
There were a few species (e.g. Virginia Rail and Sora) for which
record early 1999 dates were the result of special efforts, using
tapes, to find the species, but this was the exception, not the rule.
I looked at arrival dates (1999 versus average) in 3 ways: all
species (the "+ or - column), passerine species only (the "PASS"
column), and passerine species normally arriving in May (the "MAYPASS"
column). A figure of 10 in one of these columns means that the 1999
arrival date was 10 days ahead of average; a figure of
-10, 10 days later than average. The results were about the same for
all 3 comparisons. For all bird species (103 comparison of arrival
dates), the 1999 arrival dates averaged 0.8 days earlier than average;
for passerine species only (56 species), 1.5 days later than average;
for passerine species normally arriving in May, 0.7 days earlier than
average. Based on first arrival dates, you would be hard-pressed to
show that the timing of migration in spring 1999 was much different
from the average.
At the same time, look at the arrival dates for some of the
commonest and most obvious species: Cliff Swallow, 14 days late; Dusky
Flycatcher, 10 days; Golden-crowned Kinglet, 14 days; House Wren, 10
days; N. Rough-winged Swallow, 21 days; Ruby-crowned Kinglet, 11 days;
Vesper Sparrow, 12 days; Warbling Vireo, 11 days; and Yellow-rumped
Warbler, 10 days late.
There is no question that the peak migration for many passerines
was at least a week late. However, it seems that in late years like
this one, for many species, you are likely to get a few "early birds"
well in advance of the peak movement. For instance, my first Western
Kingbird was on May 1st, tying my record early date, and 2 weeks
before the main arrival. My first Olive-sided Flycatcher was singing
at the Coquihalla Lakes on May 11, with the lakes still frozen and 5
or 6 feet of snow on the ground-- at least 2 weeks before the main
arrival. Occurrences like this tend to skew the data.
It may be that arrival dates for an area with lots of observers
(e.g. Vancouver or Seattle, or even Kamloops or Vernon) would show a
closer relationship to the peak migration dates. In data based mainly
on one person's observations, it may be that the hit-or-miss nature of
the observations (i.e., the small sample size) obscures significant
trends.
I keep track of numbers for each species religiously when I am out
birding, but I am not sure if I have enough data to show that the 1999
spring migration was late, based on peak counts. Maybe the best way to
compare migration timing in different years is to look at counts of a
few key species (e.g. Dark-eyed Junco, American Robin, White-crowned
Sparrow, Yellow-rumped Warbler, Ruby-crowned Kinglet, Wilson's
Warbler). For some of these species, concentrations in the valleys
appeared late and lingered much later than usual this year.
If anyone has tabulated spring arrival dates and has time to make
the kind of comparisons I did, I'd be very interested in seeing your
results, or a summary of them. I'd also be interested in any comments
from our resident weather guru and former FIELD NOTES regional editor,
Jack Bowling. Were arrival dates late in Prince George, Jack? And can
you provide any data on just how much cooler and stormier this spring
was than usual? I don't have the data at hand, and I am reluctant to
pay the exorbitant fees demanded for monthly weather summaries by
Canada's Atmospheric Environment Service.

Sincerely,

Wayne Weber
114-525 Dalgleish Drive
Kamloops, B.C. V2C 6E4
wayne_weber at bc.sympatico.ca




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