Cranberry Marsh

Cranberry Marsh entrance walk in winter. Photo by Jim Skene.

Observation Hours

Observing hours have remained relatively constant since the year 2001.

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Relative Bird Abundance

The relative abundance of birds has changed over the course of the study. In the 1990s the abundance graph is like this.

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(The commonest bird is assigned the value of 100 and all other birds have values calculated relative to their numbers as compared to the commonest bird.)

In the 2000s it looks like this.

Migration at a Glance

The table gives for each species the date range when 90% of the birds are seen and details of the maximum count seen since the beginning of the study as well as totals for recent years.

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Migrating Numbers
Trends

The numbers of birds migrating over our site are changing according to the daily graphs for individual species shown below. It remains an issue, though, to determine whether the apparent increases or decreases are real or not. Only some of the graphs show a trend line that is statistically significant at the 99% level of confidence using a Chi Square test and at least one of these is suspect.

The Broad-winged Hawk migrates in such a narrow time corridor each year that we are nervous about making trend statments based on our observations to date. It appears to be too easy to miss significant numbers of migrating birds in any given year.

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Birds with rising trend

These rising trends are significant at the 99% level.

These rising trends are not statistically significant because the numbers are too low but there nevertheless appears to be a rising trend.

Osprey
Bald Eagle
Cooper’s Hawk
Peregrine Falcon

Birds with falling trend

These falling trends are significant at the 99% level.

Birds with no apparent trend

Northern Harrier
Northern Goshawk
Golden Eagle

Weather and Time Effects

In the graphs in this section, the number of birds seen has been divided by the number of hours observing so that the resulting counts are expressed in “birds-per-hour”.

It is clearly best to view migrating raptors when the wind is from the North. Note that the figure for NE winds is affected by the small number of observing hours. More total birds are seen in NW winds.

More birds are seen when the barometer is rising.

Overall, based on total birds seen, the data suggest that the best time to see the largest number of raptors is when the winds are from the north or north west and the barometer is rising.

More birds are seen around noon.

Cranberry Marsh is a flat wetland in the southwest corner of the Lynde Shores Conservation Area, managed by the Central Lake Ontario Conservation Authority (CLOCA). In the spring of 2001 the latter embarked on a programme in conjunction with Ducks Unlimited, that entailed a complete drawdown of the water into Lake Ontario, followed by a step–by–step procedure to gradually regenerate a true marshland. Indeed, the wetland relies on runoff and rains to supply water AND has no natural outlet to the lake, the two being separated by a narrow barrier–beach. A very low dissolved–oxygen count, along with no water movement in a very shallow “marsh” contributed to an ugly scene in the fall of 2000, that being the death of a very large number of ducks, particularly Green–winged Teals, attributed to avian botulism.

The CMRW monitoring is done from a 10’ x 18’ viewing platform which sits atop a berm constructed in the summer of 2001. The GPS readings were taken from this platform which is located at the southwest corner of the wetlands in southwest Whitby, Ontario: the fixed position of the platform is 43° 50’ & 24.9” N and 78° 57’ & 57.7” W.

In the fall of each year (starting in 1990), from late August through to late November, we have found that southbound hawks to our east avoid crossing Lake Ontario, thereby turning westward; in so doing they fly close to the shoreline, enabling us to view, identify and record.

If traveling from the west along Highway 401 exit at Salem Rd. in Ajax (exit 404), then south 1 km. to Bayly St., left/east along Bayly through Lake Ridge Rd., continuing 0.4 km to Halls Rd. in Whitby, right/south 1.5 km toward the lake, parking in a roadside parking area at the south pathway; a short easterly walk along a paved pathway takes you to the berm–platform.

If coming from the east along the 401 exit at Brock St. in Whitby (exit 410), south 0.5 km to Victoria St. (eastern extension of Bayly), right/west 3.2 km to Hall’s Rd., left/south and hence as above.

CMRW exists because of a friendly rapport among many people who volunteer to help, whether for a few or many hours over a period of 90 or more days.