The proverbial
canary in a coal mine refers to the early warning system used by miners back
in the day: a caged bird whose sudden death down in the shafts probably
signaled the presence of some noxious gas.
In Indiana,
however, one might speak instead of the warbler on the wing.
In a paper accepted
for publication by the prestigious journal North American Birds, Ken
Brock of Westchester Township and Randy Pals of Chesterton review data
collected throughout the Hoosier state between 1996 and 2015 on warbler
sightings in late winter and spring, specifically in the March 1-June 10
window.
Their finding: more
than a dozen species of wood warbler are arriving in Indiana from their
over-wintering sites nearly five days earlier now than they were 20 years
ago.
The significance of
that finding?
Spring migration is
ultimately a breeding behavior and avian breeding and nesting are
intrinsically linked to habitat and climate.
Brock, a geologist
by trade now retired from the faculty of Indiana University Northwest, is
the acknowledged dean of birding in Northwest Indiana who, along with Pete
Grube, pioneered the discipline here in the Dunes in the Seventies and
Eighties. He’s the author of The Birds of Indiana Dunes, an
invaluable reference on population trends, migration patterns, and seasonal
hotspots, as well as of The Birds of Indiana, which is based on a
database of 615,000 sightings and does for the entire state what his earlier
work does for the Dunes.
Pals is an
outstanding birder who learned his craft under Brock’s tutelage and on any
given early Saturday morning in May is likely to be found with a company of
other birders at the Green Tower site at Indiana Dunes State Park, calling
out the species and numbers of the migrating birds shooting the lake--Golden-winged
Warbler, nice! One, two, three Yellow-rumped, make that four. Blue
Grosbeak!? What’s that doing here?--as Brock duly records them. Pals is
also a gifted herpetologist who, only last month, identified a Five-Lined
Skink in Whiting Park, the first of that species actually seen in Lake
County since 1899.
Prompted by studies
done in Europe of the possible impact of climate change on avian
populations--a number of which have indicated that some migrant species are
arriving more than a week earlier than they did 30 years before--Brock and
Pals crunched the numbers on all 67,942 individual sightings of 16 species
of warbler and found that as a group those migrant species are arriving in
the state 4.76 days earlier than they were 20 years ago.
Another, not
altogether precise way, of saying the same thing is that spring is greening
Indiana almost a full work-week earlier than it used to not so very long
ago.
“Upon initially
seeing the data I was astonished,” Brock told the Chesterton Tribune.
“It was hard to believe that migration dates could change so rapidly.
However, warblers eat insects, insects eat vegetation, and it is well
established that global warming has caused spring vegetation to develop
earlier.”
“Accordingly, the
warblers are just keeping up with the climate,” Brock added. That is, “This
result is consistent with a warming climate.”
Brock and Pals are
currently working on a companion study, of the same 16 species’ departure
dates in the fall, when they migrate south from Indiana for the winter.
Although the fall data, on a preliminary reading, suggest a less pronounced
trend than the spring data do, they nevertheless do appear to show “that 15
of the 16 warblers are migrating later than they did in 1996,” Brock noted.
Which would suggest that fall is lasting longer or winter beginning later.
In any case, the data aren’t all in yet: Orange-crowned and Palm warblers
are still being seen in southern Indiana and will be into December.
Brock acknowledged
that 4.76 days--4.76±0.23 days, to be exact--may seem, out of context, like
a trivially random result. Yet when one takes the long view of climate,
which tends to be changeable only within pretty consistently--that is to
say, historically--prevailing parameters, then a quickening in the onset of
one season, or of the passage of another, of almost one-sixth of a month in
less than a generation is kind of a big deal.
“I realize this is
a rather arcane topic but we believe that it is extremely significant,”
Brock said.
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