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Wild Birds of Sutton Center

by David A. Wiedenfeld

I've been making bird counts right here on the grounds of the Sutton Avian Research Center two or three times a week since April 1997. The count location is always the same point, near the main building, and counts are made at the same time of day, 08:00 h. The counts are ten minutes long, and include all birds seen or heard.

Of course, I can only record birds if they are in the area; for example, I don't record Summer Tanagers in December, because they're not here then. But even when birds are in the area, their detection can vary as a result of factors besides their abundance. Because I record birds heard, as well as those seen, if a bird is very actively singing (as in early spring territorial males), I'm much more likely to record it than I am if it is present but quiet.

Of course, birds vary in their singing activity through the year (as well as the day). Therefore, the number of birds shown on these graphs should be considered not their abundance, but rather their detection. This number is a confounded result of the birds' abundance and singing (or calling) activity. Be careful when you interpret the numbers!

Julian Date Date
1 1 January
60 1 March
120 30 April
180  
240 28 August
300 27 October
360 25 December

In 218 counts from 10 April 1997 to 18 August 1999, I've recorded 71 different species of birds here at the Center. This includes nine species new to the counts in the last year, since 21 August 1998. (They are Northern Harrier, Red-tailed Hawk, Barred Owl, Belted Kingfisher, Tree Swallow, Brown Creeper, Northern Mockingbird, and Blackpoll Warbler.) But 12 species have been recorded only once each during my counts, and 30 species (42% of the total!) have been recorded fewer than ten times.

In contrast, only 10% of the species recorded (seven species) account for 47% of all birds recorded. These top seven species are Red-bellied Woodpecker, American Crow, Blue Jay, Tufted Titmouse, Carolina Chickadee, Carolina Wren, and Northern Cardinal.

With over two years of data, it is now possible to see some interesting patterns in the detections of these birds. Their numbers and / or detectability vary within years, and their numbers can also vary among years. And each species is unique in its pattern.

The dates shown on these graphs are "Julian" dates, where 1 January = 1 and 31 December = 365. (Of course, leap years mess everything up a bit.) So:

Species and Individual totals graph

The total number of individuals has varied by about 100% over the years, from about 20 to over 40. The number of individuals tends to be highest in winter, peaking just after the first of the year, and lowest in summer.

In contrast, the number of species moves in almost the exact opposite pattern, with the most species being recorded in late spring / early summer, and the fewest in early winter, around December. The number of species is also not as variable, varying only from a low of about nine to a high of around 15, about a 50% difference. Of course, the species are not all the same in summer and winter, with some species moving out and being replaced by others.

4_woodpeckers

Four species of woodpeckers regularly occur at the Center, Red-bellied Woodpecker, Pileated Woodpecker, Downy Woodpecker, and Hairy Woodpecker (with occasional records of two others, Red-headed Woodpecker and Northern Flicker).

These species show different patterns of detectability (although not necessarily abundance) throughout the year. Pileated and Downy seem to be detected more frequently in fall and winter. For the Downy Woodpecker, this may be a result of the birds coming to our feeders.

The Red-bellied Woodpecker is detected most often in spring, which may be a result of increasing vocalizations during the breeding season. Red-bellied Woodpeckers probably do not migrate, so the actual population probably doesn't change much during the year.

Hairy Woodpeckers are the least-frequently detected, but they seem to recorded more frequently in fall.

Graph of crow and cardinal numbers

Our crows and cardinal show an interesting pattern, with almost exactly the opposite rates of detection. The crows are most frequently detected in November (1997) and at New Year's (1998), while the cardinals seem to be recorded most often in late spring.

For the cardinals, this is probably be a result of detectability alone; many more birds are recorded when singing, and they sing more in spring. But for crows, this may be a result of increased numbers, or at least increased flock size, in winter.

eaphnest

Eastern Phoebes nest on our building, even in the burglar alarm siren horn. If we have a break-in, that could be a rude wake-up!

graphcachetti

Because detectabilities differ among species, it is not possible to compare species with one another. But considering only one species over years can give an estimate of changes in abundance.

Both Carolina Chickadee and Tufted Titmouse were much more frequently detected at the Center in winter 1998-99 than in the previous winter, 1997-98. This may reflect the fact that we put out our feeders much earlier in 1998 than 1997. But see the graph to the right.

graphamgo

On the other hand, American Goldfinches were recorded much more in the winter of 1997 than in 1998, opposite to the abundance of the chickadee and titmouse (graph at left).

graphpuma

An interesting pattern is that some species occur in our area, but are not always found at the Center. For example, the first Purple Martins arrive in Bartlesville around the beginning of March each year, but we do not record very many of them until they complete their breeding and begin to migrate in late July.

Chimney Swifts show a pattern that is similar to that of the martins, although they have a little peak in early summer, then a much higher one in early fall.

graphchsw

Evidently, the habitat right around the Center, where I do my counts, does not have good breeding sites nearby, so the swifts and martins breed elsewhere, and are only recorded when they begin their post-breeding dispersal.