[CT Birds] Conclusions from counting birds
eric_r_larson at hotmail.com
Sun Jun 6 17:38:27 EDT 2010
Many posts on this site describe the ups and downs of sightings of particular species, and questions as to whether the variances are significant trends - fewer Orioles, earlier Warblers, laggard Loons, wayward Kites. Taken in isolation, individual observations can't speak to a population trend. Shifts in appearance of species can mean any number of things - poor luck breeding in the year past, lack of food this year in the local region, shifts in weather that forestalled migration, or simply the birds decided to move a little further up or down or over to settle in for the year. Or most simply, sampling error (yep, you don't know what you don't know). A wonderful summary of the vagaries of drawing conclusions from sightings is "Monitoring Bird Populations By Point Counts" by John C. Ralph. It's still availabe from Amazon.
If you are intrigued by the variations in your count list over the years, this monograph may give you some insight into the significance of your observations (I mean statistical significance, not your personal significance), and simple reasons why swings in observations are to be expected.
So when you see something unexpected, trust your eyes and report it. If you don't see something, remember a negative result is a weak scientific position. Anyone who challenges you with their historic experience may be relying on too small a data set to be credible.
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