Everyone seems surprised by the riotous weather patterns of the past few weeks. The cold and warm fronts crossing over us have sent temperatures skyrocketing (it was 80 degrees on Sunday!) and then plummeting (22 degrees last night!). They also trigger violent storms and the high winds that shake our houses and forests alike. Even though these weather patterns surprise us each year, they occur each transition season from winter into spring with clock-like regularity. This is a very poor place for plants and animals to rely on temperature as an index of seasonal time!
Migrating birds arrive on the first warm days of late winter or early spring. It is interesting to compare the arrival dates this year (the year of the interminable winter!) with those of 2011. There are some predictable and also some unexpected patterns!
Robins showed up this year in the field by our house on March 13 (they had arrived on February 15 in 2011). This year we first saw red-winged blackbirds in the fields near Northmoreland Park on April 6 (in 2011 we first saw them on March 2). Common grackles came into my yard this year on March 15, but they didn’t show up until March 25 in 2011. Towhees (pictured above: photo by D. Sillman) arrived this year on April 5 very close to their April 8 arrival date in 2011. Bluebirds first flew across our field on March 19 in 2011, this year we first saw them in our yard on April 2 but had seen them pretty regularly along Route 780 up near campus for about a month. Last Saturday (April 12) I saw my first cowbird out under the front yard bird feeder (not all arriving migrants are welcome!). In 2011 I didn’t record seeing a cowbird until the first of May. And, finally, we saw our first killdeer this morning (April 16) driving to work. The Penn State “roof-top killdeers,” though, have not yet returned to our New Kensington campus (in 2011 they were here on March 30 and loudly greeted us every morning as we walked from the parking lot to the entrance door).
So, there were some delayed arrivals this year (robins, bluebirds, red-winged blackbirds, and killdeer) but also some earlier arrivals (towhees, cowbirds, and common grackles). It would be interesting to look at each species’ individual migration paths and distances to see if the patterns of the recent weather fronts might be able to explain these observations.
Looking at bird species that will be departing soon from our local habitats, I see a big difference in the movements of the dark-eyed juncos this year as compared to 2011. In 2011 the juncos began to thin out (as they headed north) in the warmer days of early March, but then came back in numbers even greater than their winter densities in the colder days of early April. My guess was that they started up to their more northern breeding territories but then came back for shelter and sunflower seed sustenance when winter showed signs of returning. This year, the juncos have not yet started to thin out around my feeders! There was no “false spring” this year to lure them north. They will be heading out very soon, though, I am sure.
To be the first to arrive at your summer breeding territories is a great benefit to a bird. But, the danger of freezing to death in a sudden storm, or being unable to find a reliable supply of food because of an early spring snow makes the early arrival a life-or-death adventure. This year Deborah and I watched some very confused looking robins hopping about on the fresh snow trying to scare up some earthworms that had been so abundant just the day before!
Last year the early warm weather brought out swarms of honeybees and bumblebees a month and half ahead of the blooming of any flowers that might provide nectar to feed them. There were reports of honeybees cleaning out birdfeeders that had been filled with sugar-rich crushed corn, and stranded, frozen bumblebees scattered across lawns and parking lots. This year, at least, the cold weather was more persistent and did not fool these vital pollinators into any self-destructive forays. In 2011, the bumblebees began swarming our deck in the afternoon on April 15. Maybe they’ll be there sometime next week!
In all of these species there is a continuous ebb and flow of daring and caution, a continuous re-structuring of adventurous and conservative behaviors which are each rewarded or punished depending on the particulars of the weather patterns of any given year. Some days the early bird WILL get the worm, while on other days that early bird, unfortunately, will not fare so well.