Chesterton Tribune

 

 

Is spring arriving earlier than it used to? Just ask the warblers

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By KEVIN NEVERS

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.

 

Posted 11/20/2015

 
 
 
 

 

 

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