The 117th CBC in Michigan

The 117th Christmas Bird Count (CBC) yielded results from 68 Michigan circles. A total of 526,853 individuals of a definitive 150 species was documented. Additionally, one species was reported during count week but not on count day, and one identifiable subspecies was noted on count day. The median number of individuals/circle was about 5300, with half of all circles reporting between about 2200 and 9300 individuals. At the upper end of the scale were Anchor Bay with 82,339 individuals and Rockwood with 34,186, with five other circles exceeding 20,000 individuals. The median number of species/circle was 54, with half of all circles reporting between 43 and 64 species. The greatest species diversities were noted at Anchor Bay (99 species, undoubtedly a new CBC high for Michigan), Rockwood (83), and Monroe (80); an additional six circles, all in the Southern Lower Peninsula, had species totals in the 70s.

Well-documented vagrants or seasonal rarities (species with annual frequencies of less than 50% in the previous 10 years) included the following 14 species (including 1 seen during the count-period only) and one subspecies: Eurasian Collared-Dove—11 birds at New Buffalo is an unprecedented number, reported without details but in an area where seen regularly in recent years (recorded twice in the previous 10 years, and in 4 (9%) of 46 years, 1970-2015); Virginia Rail—one at Tittabawassee Valley (recorded four times in the previous 10 years, most recently in 2015, and in 25 (54%) of 46 years, 1970-2015); Dunlin—a total of two birds, with singles at Anchor Bay and Monroe (recorded in 12 (26%) of 46 years, 1970-2015, last in 1991); Gyrfalcon—one at Alpena (recorded once in the previous 10 years, in 2007, and in 5 (11%) of 46 years, 1970-2015); Eastern Phoebe—one at Waterloo State Recreation Area (recorded three times in the previous ten years, most recently in 2015, and in 15 (33%) of 46 years, 1970-2015); Marsh Wren—a total of two birds, with singles at Allegan State Game Area and Anchor Bay (recorded three times in the past 10 years, most recently in 2014, and in 32 (70%) of 46 years, 1970-2015); Mountain Bluebird—one at Anchor Bay (this 9th Michigan record, and the 1st in winter, was present in a public park for most of December and viewed by many); Townsend’s Solitaire—a total of two birds, with singles at Eagle Harbor and New Buffalo (recorded four times in the previous ten years, most recently in 2012, and in 12 (26%) of 46 years, 1970-2015; American Pipit—one at Anchor Bay (recorded twice in the previous 10 years, most recently in 2015, and in 14 (30%) of 46 years, 1970-2015; Ovenbird—one at East Lansing (recorded once in the previous 10 years, in 2012, and in 2 (4%) of 46 years, 1970-2015; Yellow-throated Warbler—one attending a feeder before and after count day (but not seen on count day!) at Little Bay de Noc (recorded in 2 (4%) of 46 years, 1970-1915, most recently in 2003); Savannah Sparrow—two at Rockwood (recorded four times in the previous 10 years, last in 2013, and in 17 (37%) of 46 years, 1970-2015); Harris’s Sparrow—one at Marquette (recorded twice in the previous 10 years, last in 2015, and in 10 (22%) of 46 years, 1970-2015); Dark-eyed (Oregon) Junco—one at Barry County (recorded three times in the previous 10 years, last in 2015, and in 26 (57%) of 46 years, 1970-2015); Brewer’s Blackbird—one at Niles (recorded three times in the previous 10 years, last in 2011, and in 19 (41%) of 46 years, 1970-2015). Amazingly, an additional 45 species that had been documented in 1-4 of the previous 10 years went unreported this year.

“Borderline” species, those detected in five or six of the previous 10 years, are so-defined because with only a modest change in annual frequency they could move upward into the regular category or downward into the infrequent or rare category. Two “borderline” species were reported this year: Greater White-fronted Goose—nine at Allegan State Game Area (reported in 5 of the previous 10 years and averaging 2.6 birds/year; Chipping Sparrow—a total of three birds, with singles at Ann Arbor, Huron County, and Western Macomb County (reported in 5 of the previous 10 years and averaging 2.1 birds/year. An additional five “borderline” species went unreported this year: Ross’s Goose (reported in 5 of 10 years, with average of 1.2 birds/year); Purple Sandpiper (reported in 6 of 10 years, with average of 1.3 birds/year); Black-backed Woodpecker (reported in 6 of 10 years, with average of 1.4 birds/year); Boreal Chickadee (reported in 6 of 10 years, with average of 1.7 birds/year); Hoary Redpoll (reported in 6 of 10 years, with average of 5.0 birds/year).

Of 150 species recorded on count day, 135 are considered to be of regular occurrence on Michigan CBCs, having been recorded in seven or more of the previous 10 years. Two other species seen frequently in recent years went undetected: Gray Jay and Common Yellowthroat. The remainder of this review will focus on 48 species reported in numbers that were above or below expected levels based on historical CBC results. The status of a species is considered to be “changed” (i.e., substantially above or below average) if the number reported (standardized as birds/circle) was more than one standard deviation above or below the average of the previous 10 years. That analysis reveals that 21 (16%) of the 135 frequent, or expected, species detected on the 117th CBC were present in above-average numbers, 27 (20%) were below average, and 87 (64%) did not differ markedly from their respective 10-year (2006-2015) averages.

Ten of the 29 species of waterfowl seen annually or near-annually on Michigan CBCs deviated substantially from the 10-year average: Cackling Goose (6 birds, or 0.09/circle, the lowest index in eight years) was down 76%; Mute Swan (2390 birds, or 35.2/circle, the third lowest index since count-year [CY] 99) was down 35%, continuing a downward trend for the third year running; Trumpeter Swan (271 birds, or 3.99/circle, an index exceeded only by last year’s 4.03) was up 31%; American Black Duck (2328 birds, or 34.2/circle) was up 65% from the previous 10 years but still suppressed relative to years past (i.e., averages of 59/circle in the 70s and 42/circle in the 80s); Mallard (45,569 birds, or 670/circle) was up 37%; scaup were present in the lowest numbers in eight years, with Greater  (1093 birds, or 16.1/circle) down 79% and Lesser (268 birds, or 3.94/circle) down 93%; Bufflehead (1282 birds, or 18.6/circle, the lowest index in 28 years) was down 61%; Common Goldeneye (10,628 birds, or 156/circle, the 2nd lowest index in the last 12 years) was down 29%; and Common Merganser (9019 birds, or 90.2/circle, the lowest index in 39 years) was down 41%.

Ruffed Grouse (63 birds, or 0.93/circle, down 45% and the lowest index since before CY 71) continued a long-term decline (i.e., compare to average indices exceeding 4/circle in the 70s and 80s). Sharp-tailed Grouse, an Upper Peninsula specialty, was up 598% (104 birds, or 1.53/circle) thanks to Les Cheneaux. Our two common grebes exhibited radically different trends relative to past years: Pied-billed (75 birds, or 1.10/circle, the 3rd highest index in the last 15 years) was up 132% while Horned (12 birds, or 0.18/circle, the lowest index since CY 81) was down 88%.

Five of eight species of gulls that winter regularly in Michigan exhibited unexpected deviations from the norm: Bonaparte’s Gull (202 birds, or 2.97/circle, the 3rd lowest index in the last 16 years) was down 88%; Ring-billed Gull (7342 birds, or 108/circle, the lowest index since CY 82) was down 68%; Glaucous Gull (13 birds, or 0.19/circle, the lowest index in nine years) was down 52%; and Great Black-backed Gull (150 birds, or 2.21/circle, the lowest index since CY 78) was down 47%. Meanwhile, while never recorded in large numbers, Iceland Gull was up 424% this year (7 birds, 0.10/circle, an index of abundance matched only twice previously, in CYs 82 and 89). Rounding out the waterbirds, Common Loon (4 birds, or 0.06/circle, the smallest index since CY 96) was down 81%, Double-crested Cormorant (756 birds, or 11.1/circle, 2.8 times the previous highest index thanks largely to the 752 birds concentrated at Monroe) was up 344%, and Black-crowned Night-Heron (13 birds, or 0.19/circle, the 2nd smallest index in the last 14 years) was down 57%.

Of 20 species of raptors (hawks, owls, and falcons) routinely seen on Michigan CBCs, nine were recorded in numbers that were unusually high or low. On the high end, Northern Harrier (93 birds, or 1.37/circle, the 3rd highest index since CY 108) was up 25% thanks in large measure to the 31 birds at Anchor Bay, Red-shouldered Hawk (55 birds, or 0.81/circle, an index of abundance exceeded since 1970-1971 only by the 0.82 in CY 113) was up 54%, and Northern Saw-whet Owl (20 birds, or 0.29/circle, an index exceeded only by the 0.40 in CY 115) was up 121% with an impressive nine birds at Detroit River. Among the falcons, American Kestrel (205 birds, or 3.01/circle, a far cry from indices in excess of 10 in the mid-70s through the mid-90s) was down 31%, while Merlin (26 birds, or 0.38/circle, a new high) was up 65%.

Among the woodpeckers, Red-headed was down while Red-bellied and Pileated were up: Red-headed Woodpecker (22 birds, or 0.32/circle, the lowest index since CY 101 and the 3rd lowest since CY 71) was down 60%; the Red-bellied Woodpecker (2307 birds, or 33.9/circle, the 2nd highest index), was up a modest 13%, continuing a largely unfettered expansion that has been in evidence since at least CY 71; and Pileated Woodpecker (369 birds, or 5.43/circle, the 2nd highest index since CY 71) was up 23%, continuing a long-term expansion rivaling that that of the Red-bellied.

Northern Shrike (42 birds, or 0.62/circle, the 2nd lowest index in the last 15 years) was down 45%, while Blue Jay (8012 birds, or 118/circle, the lowest index in 4 years) was down a modest 21%. Horned Lark (2161 birds, or 31.8/circle), was up 67%. The typically oscillating Red-breasted Nuthatch was down 34% (606 birds, or 8.91/circle, the lowest index in 14 years), while the seemingly more stable Brown Creeper was down 23% (224 birds, or 3.29/circle, the lowest index in 16 years). Winter Wren was up 56% (42 birds, or 0.62/circle, the highest index since CY 111), Ruby-crowned Kinglet (10 birds, or 0.15/circle, the highest index in 14 years) was up 215%, Hermit Thrush (72 birds, or 1.06/circle, the highest index in 11 years) was up 142%, and Northern Mockingbird (13 birds, or 0.19 birds/circle, the highest index in nine years) was up 31%.

House Sparrow (28,828 birds, or 306/circle, the 3rd smallest index since CY 71) was down 20%. Plotting the linear trend of House Sparrows on Michigan CBCs shows a remarkably steady decline, from about 900/circle in CY 71 to about 300/circle in CY 117, a decline of 66% in 46 years. The trend line has an r2-value of 0.805, lending credence to the direction and magnitude of this trend. Assuming that House Sparrows really are declining and not simply being overlooked by participants—and ignoring the fact that this invasive species remains far too numerous—the question remains, what is driving this downward trend?

The Purple Finch was the only one of the winter finches to stage anything resembling an invasion with an increase of 85% (512 birds, or 7.53/circle), the majority of individuals (63%) remaining in the Upper Peninsula. House Finch continues a long, slow decline, being down 19% (5120 birds, 75.3/circle, the 3rd fewest since CY 89) from the 10-year average and down nearly 75% from its peak in the mid-90s. Being down 84%, White-winged Crossbills were decidedly few in number (50 birds, 0.74/circle), with those few restricted to the Upper Peninsula.

Four circles are notable for harboring exceptionally large proportions (40% or more) of the statewide totals of 13 species (all seen on a minimum of 10 circles): Anchor Bay (four species—American Black Duck 71%, Redhead 82%, Greater Scaup 50%, Ruddy Duck 61%), Monroe (four species—Gadwall 58%, Great Blue Heron 41%, Red-winged Blackbird 44%, Common Grackle 40%), Rockwood (three species—Canvasback 63%, Ring-necked Duck 74, American Coot 54%), Holland (two species—Common Goldeneye 40%, Red-breasted Merganser 64%).

The 10 most numerous species in declining order of numerical abundance (with frequency of occurrence) were European Starling—61,350 (99%), Canada Goose—60,583 (81%); Mallard—45,569 (96%); American Crow—35,913 (100%), Canvasback—28,275 (22%); House Sparrow—20,828 (87%), Black-capped Chickadee—16,679 (100%), Herring Gull—16,576 (65%), Mourning Dove—15,885 (99%), and Dark-eyed Junco—15,709 (97%). The top ten species accounted for a whopping 65% of all individuals identified to species. By contrast, the 35 species (23% of the total) for which fewer than 10 individuals were seen represent a mere 112 individuals (0.02% of the total), hence the excitement when one of these rarities is spotted.

This summary would not be possible without the unflinching dedication of the CBC compilers, many of whom have shouldered this task for decades. I am especially thankful for their help in documenting reports of rarities, a thankless but invaluable service. Thanks also to the cadre of participants who voluntarily brave the elements to help document Michigan’s Christmas-season avifauna. And finally, I thank Brian Allen and Adam Byrne for reviewing and evaluating reports of rarities, thus ensuring the credence and validity of records in the database.