Sunday, September 23, 2012

Early Arrival of Winter Birds

It is that time of year when I start to look for the migrant birds that arrive to spend the winter in our garden.

This summer has been gruelingly hot. We have had weeks of temperatures over 100˚F. This week of the Autumnal Equinox we have had two record-setting days of high temperatures.

So this morning when I saw our first Oregon dark-eyed junco of the season, I was especially surprised. September is an early arrival for this species. Typically we see them arrive in October. So I got out my bird journals and put together the graph below. (10.01=Oct. 1 of that year)

data compiled by Keri Dearborn

Indeed this is an early arrival for the juncos and this is the second year in a row that they have arrived early. They are coming from local mountains and northern coasts. 

I compared their arrive dates to the rainfall data and interestingly, the heavy rainfall year correlated with the year they didn't arrive until November. The pattern with early arrival isn't as easy to discern. But one thing is certain, in twelve years of recording these arrival dates, this is the first time we have had consecutive years of early arrival in September. Are they coming for resources? Influenced by temperature? Or have two years of minimal average rainfall pushed them out of the hillsides earlier?

It will be interesting to see if other migrating birds also arrive early. 

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