A Study for the Birds – Breeding Bird Circles

Posted: Jul. 22, 2016

Each year, Science Center staff steps into the woods at dawn, braves the mosquitoes and counts the birds. In its fourth year, the Science Center’s Breeding Bird Circle Study focuses on four spots, three times in the month of June: the Sylvester Bridge (directly over a vernal pool), the Nelson Memorial Bench (in the old field, now a young forest), Woodchuck Field, and at the end of the small island on Jacobs Pond. The goal is to learn which birds breed in the area, the study commencing at the end of spring migration. Here is an excerpt from this year’s results:

2016 Effort and Conditions

12 counts, 1 from each of four observation points at the beginning, middle and end of June. The high temperature was 63 degrees, the low 54. Wind only blew on one day, at approximately 5 miles per hour, and each day was dry and without cloud cover. All counts took place between 5:18 and 6:18 a.m. The spring was exceedingly dry, with a massive outbreak of Gypsy moth caterpillars.


On three days, counting from four points each day (the bridge, the Nelson bench, the field, the small island) we heard or saw 298 individual birds of 49 species.

Year 2013 2014 2015 2016
#individuals 166 252 243 298
#species 47 41 47 49

Eight species heard or seen on the counts in 2015 were not present during the twelve ten-minute sessions in 2016: Black-and-White Warbler, Double-crested Cormorant, Great Blue Heron, Ring-billed Gull, Ruby-throated Hummingbird, Swamp Sparrow, Wood Duck, Yellow-rumped Warbler. Nine species not seen in 2015 were seen in 2016: American Redstart and Herring Gull returned to the species list; Black-billed Cuckoo, Blue-Gray Gnatcatcher, Cooper’s Hawk, Fish Crow, Hairy Woodpecker, Red-shouldered Hawk and Wild Turkey were seen or heard for the first time in the four years of the count.


The most frequently counted species (highest possible number being 12) were:

Species 2016 count Change
Eastern Wood-pewee 9 =
Northern Cardinal 9 +3
Mourning Dove 8 +3
Tufted Titmouse 8 +6
American Goldfinch 7 +5
Chipping Sparrow 7 -2
House Wren 7 +3
Ovenbird 7 -3
Pine Warbler 7 +2
Black-capped Chickadee 6 -1
Common Grackle 6 +2
Downy Woodpecker 6 +1
Gray Catbird 6 -3
Red-winged Blackbird 6 -2
Warbling Vireo 6 =
Yellow Warbler 6 +1

The following species that appeared in the “most frequently counted” list in 2015 dropped off in 2016:

Baltimore Oriole 4 -1
Cedar Waxwing 3 -2
Tree Swallow 3 -2
Wood Thrush 1 -4


Most of these changes can simply be attributed to annual variation. A much longer study would be needed to detect any true change in local population status.


The most abundant birds (simply adding all individuals of a specific species throughout all circles, all days) were:

Species 2016 count Change
Common Grackle 32 +19
Red-winged Blackbird 22 +3
Mute Swan 14 +11
Ovenbird 14 +1
Gray Catbird 13 -6
Northern Cardinal 12 +5
Chipping Sparrow 11 -4
Tufted Titmouse 11 +9
Eastern Wood-pewee 10 =
American Goldfinch 9 +6
Yellow Warbler 9 +1
Black-capped Chickadee 8 -2
House Wren 8 +4
Mourning Dove 8 +2
Pine Warbler 8 +1
White-breasted Nuthatch 8 +5

The following species dropped off the “most abundant birds” list in 2015:

Species 2016 count Change
Chimney Swift 4 -8
Downy Woodpecker 6 -3
Tree Swallow 6 -8


The single high count for any species in any circle was 10 Common Grackles, which were flying in and out of their breeding colony on Jacobs Island with food; their actions also led to the second and third highest counts of 8 and 7. Mute Swans were represented in groups of 7 twice (2 adults, 5 cygnets), and Red-winged Blackbirds were counted in groups of 6, 5 and 4.

On 8 occasions we counted 3 members of the same species in any circle. All other species appeared in singles or pairs. That’s territoriality for you. Aside from the Eastern Wood-pewee, the species listed above are among the most common birds in Massachusetts. Eastern Wood-pewees are deep woods species and are susceptible to nest failure due to acid rain breakdown of calcium levels in forest floor food sources, and therefore brittle eggs. Their health is a good indicator of the health of the ecosystem.

Of particular interest is the decline in Tree Swallows. Woodchuck Field once had bird boxes specifically for their benefit. They visit early in season now but move on. A Tree Swallow Nesting Box program, either in Woodchuck Field, on Jacobs Pond, or both, would be of great benefit to the species, as it would for Eastern Bluebirds, which have not bred here in two years.


After four years of a study, there is not much to tell. Annual variation can make small numbers like the figures in these tables look larger than they are. These three years (2013, 2014, 2015, 2016) will be more pertinent when juxtaposed with three in the future (say, 2023, 2024, 2025, 2026). But, if we are able to keep these counts up for a continuing period of twenty to thirty years, we may better be able to see trends.

In short, a single decision – Mute Swans opting to breed on the pond in 2016 after not doing so in 2015 – can grandly influence these statistics. Mute Swans are known for their territoriality and may be the reason we have not had Canada Geese on the survey for two years. Was the quality of the food in the pond significantly different? It’s difficult to say.

The only thing we know for sure is that the weather was dramatically different over the past three years. The number of days with greater than or equal to .01 inches of precipitation in June 2013 was 21.57; in June 2014, it was 14.59; in June 2015 it was 10. The first month of the summer of 2015 was much drier and sunnier than the previous two Junes, and the spring of 2016 was dry with a massive outbreak of gypsy moth caterpillars.

The fifth year of this study will take place around the dates of June 1, June 15 and June 30, 2017.