Barred Owl Research - Overview
Introductions
According to the text books, Barred Owls are supposed to need large stands of old-growth forest to survive. Yet the species is abundant throughout the older suburban neighborhoods of many cities in the southeast. Intrigued by this apparent contradiction, we initiated a study of Barred Owls in the Charlotte region in the central Piedmont of North Carolina in 1999. One of our initial question, simply put, was whether the books were wrong or have the local Barred Owls simply neglected to read the books?
Over the subsequent decade four graduate students, a small flock of undergrads, and I have studied Barred Owls in both suburban and rural habitats around Charlotte. Besides figuring out what Barred Owls are doing in this unusual habitat, we compared the natural history of the two populations. Are the city birds reproducing as well as their country cousins? Are territory sizes the same? How exactly do the two habitats compare structurally? Do the city and country birds rely on the same prey species? How far do the young travel when they leave their natal territories?
We began our study in 1999 placing nest boxes for Barred Owls in suburban Charlotte and the surrounding rural areas. We collected our first nesting data in 2000, and banded and radio-tagged our first adult owl in January of 2001.
ALL ENCOUNTERS |
|
Young |
204 |
Post-dispersal young |
1 |
2nd year birds |
3 |
Adults |
93 |
TOTAL |
301 |
Retraps |
43 |
The 43 retrappings represented 29 birds. Of these, 18 were retrapped once, 8 two times, and three serial offenders were retrapped three times.
INDIVIDUALS
Adult/no radio |
7 |
Juvenile/no radio |
161 |
Brancher/tagged |
11 |
Nestling/tagged |
22 |
Orphan/tagged |
6 |
Post-fledgling/tagged |
2 |
Tagged adults |
49 |
TOTAL |
258 |
Summarizing these totals:
Radio |
Band only |
||
Adults |
50 |
7 |
56 |
Juveniles |
39 |
162 |
202 |
89 |
169 |
258 |
Radio-tagged |
Rural |
Suburban |
|
Orphan |
5 |
1 |
6 |
Adult female |
9 |
18 |
27 |
Adult male |
3 |
20 |
23 |
Nestling/brancher |
12 |
21 |
33 |
TOTALS |
29 |
60 |
89 |
How Encountered |
|
Mistnet |
20 |
Bownet |
2 |
Noose trap |
41 |
Chimney |
5 |
Nest |
170 |
Pre-brancher |
2 |
Brancher |
12 |
Orphan |
6 |
TOTAL |
258 |
Morphology
While processing owls for banding or radio tagging, we measured wing (unflattened wing chord) and tail length and weighed them.
In Charlotte, female Barred Owls are about 30% heavier than males (means 902g vs. 695g), with wings 4% longer (33.4cm vs. 32.14cm) and tails 3% longer (22.5cm vs 21.7cm) than males. There is overlap in all three measures, but all are statistically significantly (p<.05) different.
Table. Morphology of adult Barred Owls in Charlotte, NC, (mean, standard deviation, N).
Females |
Males |
|
Weight (g) |
901.8 (92.56, 43) |
695.4 (53.80, 35) |
Wing (cm) |
33.4 (1.07, 32) |
32.1 (1.07, 25) |
Tail (cm) |
22.5 (0.89, 32) |
21.8 (0.82, 26) |
Reproduction
Based on known or estimated hatch dates for 49 nests (Fig. ) and an estimated 30 day incubation period, egg laying in Charlotte begins as early as the first week of January (rarely) with a peak at the end of February and beginning of March, with most eggs laid between the second week of February and the third week of March.