Date: 4/10/17 1:49 pm
From: Herb Wilson <whwilson...>
Subject: [Maine-birds] Web app on spring arrival dates
Hello all,

We are now in the 24th year of the spring arrival date study of Maine
migratory breeding birds. Many of you have contributed data. We have over
65,000 arrival dates recorded.

To make the data accessible to any interested person, I have developed an
interactive web app. I invite you to visit:
https://hobbes.colby.edu/arrival/

Using the drop-down menu on the left, you can choose from over 100 species
of migratory breeding birds. Slider bars allow you to choose a year and the
widths of the bars in the histograms. Choose a binwidth of 1 if you want to
see the actual date of each sighting or a larger number to see the general
pattern of first arrivals.

Just above the histogram, you can click on Data Summary to get the median
date, mean date and other summary statistics for a particular species/year
combination.

You can also explore the relationship of arrival date over time (are birds
arriving earlier now than they were two decades ago?) by clicking on the
Year radio button on the left and clicking on the Scatterplot tab.

Some species adjust their migrations based on the nature of the spring at a
particular point. We know that eastern seaboard weather is correlated from
Delaware to Maine. A cold March in Pennsylvania predicts a cold (even
colder!) March in Maine and may result in a later than average arrival for,
as an example, Common Grackles.

You can explore this relationship by clicking on the
Temperature.Departure.from.Mean radio button and clicking on the
Scatterplot tab. Negative temperature departures indicate a cooler than
average month while positive departures indicate a warm month.

A cold March does not necessarily lead to a cold April and a cold May.
Therefore, the temperature.departure values are based on the primary month
of arrival for different species. So, March temperature departures are used
for Red-winged Blackbird, April for Hermit Thrush and May for Black-billed
Cuckoo.

The North Atlantic Oscillation (NAO) is a northern Atlantic weather
phenomenon that is driven by the difference in pressure between the
relatively fixed Icelandic Low and the Azores High. Here's a good
exploration of the topic:
https://www.wikiwand.com/en/North_Atlantic_oscillation

When a Positive NAO (strong difference in pressure between the Icelandic
Low and Azores High) occurs, the hemispheric winds produce a wet and mild
winter in our part of the world. A Negative NAO produces a cold, dry winter
in New England and Atlantic Canada. One expects spring to arrive earlier
during a Positive NAO event.

You can explore the effect of the NAO Index on arrival date by clicking on
the NAO.Index radio button. You will find that this index is not a very
good predictor of arrival dates for most species.

When you look at one of the trend lines in a scatterplot, be careful about
the interpretation. Particularly for lines where the confidence limits are
broad (indicated by the darker gray area around the line), a relationship
may not be statistically significant.

If you want to get into the statistical weeds to see if a line is
statistically significant, click on the Regression Statistics tab. If the
p-value (the last line of the output) is greater than 0.05, then the line
is not a statistically significant one.

I hope you enjoy exploring the data, made possible only by a dedicated
corps of citizen scientists.

Best,

Herb

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