Monday, January 9, 2012

Evening Grosbeaks: What Is Happening with Them?

(Transcripts of For the Birds for January 9 and January 10, 2012)

When I moved to Duluth in 1981, Evening Grosbeaks were immediately woven into the fabric of my daily life. We heard them in our box elders as we lugged boxes into our new house and they were the first species to visit our feeders. Their calls provided background sound indoors and out. Their numbers were down in summer, up in winter, and huge during spring and fall migrations, but season after season, year after year throughout the 80s, Evening Grosbeaks were in my yard. I had better luck with them than many people because my box elder trees drew in flocks flying overhead, but just about anyone in Duluth with platform feeders offering sunflower seeds had Evening Grosbeaks back then.

By the early 90s, grosbeak numbers seemed to be declining. I was very concerned, but thought it was part of a disturbing pattern in Duluth—during this same period, my neighborhood lost all of our nesting Tree Swallows, Red-eyed Vireos, and Yellow Warblers, and the huge waves of migrating warblers and thrushes in my backyard had dwindled. Friends of mine who lived in Duluth for several decades before I did also noticed the disappearance of local nesting species then—birds which have not returned. Evening Grosbeaks were counted on every single Christmas Bird Count from the start in 1979 until 2002, when not one appeared. There were a handful in the following years, but 2011 has now been the third year in a row that they weren’t found at all on Duluth’s Christmas Bird Count. The pattern of Christmas Bird Count data for all of Minnesota shows a very steep climb in Evening Grosbeak numbers peaking in the mid-60s.

The pattern of data for Wisconsin Christmas Bird Counts shows the same steep peak, only in the early 70s.

In Michigan, where Christmas Bird Counts have a longer history, the graph peak is more sustained, from the early 60s through late 70s, but shows that same troubling decline since then.

Some birders and ornithologists dismiss the current, widespread, and huge decline of grosbeaks in much of their former range with the argument that their former abundance may have been nothing more than an historical blip. The Christmas Bird Count patterns do imply that Evening Grosbeak numbers were quite low before the 1950s and 60s in these three states, but I suspect that’s due to the low participation before that time, particularly in the northern reaches of these three states, where the grosbeaks were most often found. The Christmas Bird Count began in 1900, but had very few participants for decades, and provides no information whatsoever for the 1800s or earlier.

Breeding Bird Survey numbers in all three states have declined significantly since the 1960s, when the survey began—sadly, this survey can’t provide any information from before then.

It is interesting to speculate about a possible population cycle that lasts many decades, or about an inexplicable historical blip, but the simplest explanation for the drop in Evening Grosbeaks numbers in the Great Lakes region in the past two decades, the explanation Occam’s razor would ask us to consider first, is that the population actually has declined, and is a serious conservation issue that deserves serious study.

Yesterday I mentioned that 2011 was the third year in a row that not a single Evening Grosbeak was found during Duluth’s Christmas Bird Count. Before 2009, the only other year in our count history that no Evening Grosbeaks were found was 2002.

No one understands why Evening Grosbeaks underwent a huge decline since the late 1980s to the point where they’ve disappeared altogether from many areas. I had a flock of about 16 in my neighborhood every day for about six weeks this summer, including adults feeding young birds, but this group was the only one I’ve had in years, and I haven’t seen one since my group left on September 15.

It’s reassuring to seek out proof that things aren’t as bad as they seem, and some birders and ornithologists have argued that the large numbers of Evening Grosbeaks in the eastern half of the continent from the 1950s through the 80s were simply an historic aberration. Without a time machine, it’s impossible to know the truth about what their numbers were during the 1700s and 1800s, much less further back in time. According to the species account written by Scott Gillihan and Bruce Byers in the Birds of North America, the Evening Grosbeak “at least mid-1800s was considered uncommon to rare east of Rockies and especially east of Mississippi River, although reported as ‘not uncommon’ winter visitor in Wisconsin in mid-1800s and ‘common’ in n. Illinois during winter in 1870s.”

I’m sure Native Americans were aware of Evening Grosbeaks before any record was made of them in written English. Indeed, the Ojibwe name for them, as transcribed by Henry Schoolcraft in 1823, was “Paushkundamo,” derived from their word for breaking something such as a cherry or berry, referring to the grosbeak’s style of eating. Schoolcraft also provided the first record ornithologists have of the existence of the species, a grosbeak shot with an arrow by a child in Sault Ste. Marie on April 7, 1823, when the bird could have been either a resident or a migrant. (See T.S. Roberts The Birds of Minnesota.) This and the fact that local native people had a word for this bird don’t prove that the species was regularly found in Michigan through earlier times, but it is consistent with that probability. A comprehensive study of the species, published in 1940 by James Baillie, mapped 82 summer records which formed an almost continuous belt in the US and Canada from southeastern Manitoba through eastern Ontario, concentrated mainly in the Great Lakes. Later expansion east of that band was attributed to plantings of box elder, the seeds of which are one of the grosbeak’s preferred food sources.

Until feeding birds sunflower seeds became a common hobby, I don’t think most people living among them would particularly have noticed Evening Grosbeaks. They are secretive nesters and have no song associated with courtship or territory. They usually stay within the branches of trees, eating a variety of seeds and fruits. Adults are pretty much entirely vegetarians—people maintaining non-breeding Evening Grosbeaks in captivity, even over a two-year period, found that they did not eat any insects offered to them—but they are known to feed their growing chicks a variety of insects including spruce budworms. Whether losses of grosbeaks are related to controls used against this forest pest is not known.

The species is incredibly difficult to study, both because it’s so secretive during nesting and because it wanders so very widely. But despite the difficulties a solid study of grosbeak population trends poses, it seems imperative to start trying to tease out what has happened and what is happening now to its population. If its dwindling numbers are indeed reflective of a problem, it’s important to figure that out while there’s still time to turn things around for this beautiful bird.

Evening Grosbeak