iroquois shoreline

General Findings	Effects of Weather and Time of Day
Map	Study Area

General FindingsTop

Observation Hours	Relative Bird Abundance
Migration at a Glance	Migrating Numbers Trends

Observation Hours

Statement needed.

Relative Bird Abundance

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.

Migration at a Glance

Back

Bird	Peak (90%)	Highest Day	Highest Day Count	2008 Total Count	2009 Total Count
Turkey Vulture	Sep 01/Oct 15	Oct 14, 2007	1042	1911	1447
Osprey	Aug 31/Sep 30	Sep 16, 2008	7	33	33
Bald Eagle	Sep 01/Oct 16	Sep 16, 2008	9	39	38
Northern Harrier	Sep 01/Nov 06	Sep 12, 2009	14	52	44
Sharp-shinned Hawk	Sep 01/Oct 30	Sep 02, 2009	134	819	546
Cooper's Hawk	Sep 01/Nov 11	Oct 11, 2008	24	62	51
Northern Goshawk	Sep 13/Nov 21	Sep 02, 2007	2	6	3
Red-shouldered Hawk	Sep 01/Nov 01	Sep 07, 2009	33	82	42
Broad-winged Hawk	Sep 01/Sep 17	Sep 21, 2006	8428	7714	1648
Red-tailed Hawk	Sep 29/Nov 15	Sep 07, 2009	268	825	332
Rough-legged Hawk	Oct 01/Nov 26	Oct 25, 2009	9	32	7
Golden Eagle	Sep 01/Oct 16	Oct 13, 2008	13	67	12
American Kestrel	Sep 01/Oct 17	Sep 05, 2009	24	156	76
Merlin	Sep 01/Oct 31	Oct 12, 2007	4	4	16
Peregrine Falcon	Sep 01/Oct 31	Nov 18, 2007	3	4	8

Migrating Numbers
Trends

The numbers of birds migrating over the 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.

Back

Birds with rising trend

These rising trends are significant at the 99% level.

	% Rise over the Study	Rise in Birds per Day During Peak
Turkey Vulture	62	+46
Bald Eagle	121	+1
Northern Harrier	25	+.5
Broad-winged Hawk	30	+145
Red-tailed Hawk	12	+6
American Kestrel	74	+.5

Birds with falling trend

These falling trends are significant at the 99% level.

	% Drop over the Study	Drop in Birds per Day During Peak
Osprey	-84	-5
Cooper's Hawk	-23	-1
Red-shouldered Hawk	-35	-1
Golden Eagle	-38	-1

Birds with no apparent trend

Northern Goshawk
Rough-legged Hawk
Merlin
Peregrine Falcon

Effects of Weather and Time of DayTop

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 West.

More birds are seen when the barometer is steady or rising.

This effect is pronounced when the winds are from the North ...

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 west and the barometer is rising.

More birds are seen before noon. Data for earlier hours suggests that large numbers can be seen then too but the number of observing hours is very small relative to the hours shown and the data are therefore not as reliable.