To every thing there is a season, and a time to every purpose under the heaven:

A time to be born, and a time to die; a time to plant, and a time to pluck up that which is planted;

Ecclesiastes 3

Spring is in the air.  The first Redwing Blackbirds have returned to our local pond, beginning their ritualistic territorial and mating calls. The regular schedule of events in nature is what ecologists call phenology. The diaries of naturalists contain observations of the seasonal activities in nature for centuries.  The science of phenology is now advancing with the lengthening record of the Earth’s greenness, snowcover and temperature from satellites and other sensors.

For birds that migrate from the tropics, where there is little seasonal change in temperature, the timing of spring migration is determined by the changing length of day.  When the days get longer, they know that it is time to go.  Species that winter in the warm temperate zone can judge the warming first-hand, and begin their northward migration when the weather seems right.  Some even speed their northward journey if conditions are favorable.

Ongoing changes in global climate show up in the historical observations of naturalists.  In the Hudson Valley of New York, spring migrant birds are arriving 11.6 days earlier than a century ago.  And in the same region, a small pond frog, the Spring Peeper, is now calling earlier. Across Europe, lilac bushes are flowering earlier, and the sensitivity of first flowering to temperature has declined over the past 50 years—what you might expect in a predictably warmer climate.  Plants in Washington, D.C. are flowering 2.4 days earlier than 30 years ago. Species are readjusting their behavior to the reality of warmer spring temperature.  Nature is validating what we know about climate change from long-term records of temperature.

On one hand, one might argue that these changes reflect the plasticity of nature, as it adapts to climate change. But looking more deeply into the issue, one might see cause for alarm.

The relationships that characterize spring phenology are the products of long-term coevolution.  Birds arrive when there are insects to eat, and plants flower when there are bees to pollinate them.  Leaf emergence in the temperate forests of North America has advanced about 7 days over the past thirty years, whereas bird arrival has advanced only about half that amount. Unless the timing of various species is precisely coordinated in response to changing climate, the historical relationships between species will be disrupted, to the detriment of their reproductive success and their persistence.

Even in a warmer climate, there are late spring cold snaps and snowstorms that can affect the early arriving individuals that have responded to overall warming climate.  Climate scientists tell us that unusual and extreme events are likely to be more frequent in a warmer climate.

We can extend this thinking to the success of crop, nut and fruit plants, whose spring flowering is closely tied to successful pollination.  Certainly farmers can replant crops, but once gone, a crop of nuts or fruits is destined to wait until the next season.  In both cases, there are significant economic costs to agriculture.

Phenology has moved from the attention of amateur naturalists and into mainstream ecology and global change policy.  Let’s hope the changes are small.



Abu-Asab, M.S., P.M. Peterson, S.C. Shetler, and S.S. Orli.   2001.  Earlier plant flowering in spring as a response to global warming in the Washington, D.C. area.  Biodiversity and Conservation 10: 597-612.

Calinger, K.M., S. Queenborough, and P.S. Curtis. 2013.  Herbarium specimens reveal the footprint of climate change on flowering trends across north-central North America.  Ecology Letters 16: 1037-1044.

Franks, S.E. and 7 others. 2018.  The sensitivity of breeding songbirds to changes in seasonal timing is linked to population change but cannot be directly attributed to the effects of trophic asynchrony on productivity.  Global Change Biology 24: 957-971

Lovett, G.  2013.  When do peepers peep? Climate and the date of first calling in the Spring Peeper (Pseudacris crucifer) in southeastern New York State.  Northeastern Naturalist 20(2):333-340.

Mahall, B.E. and F.H. Bormann. 1978. A quantitative description of the vegetative phenology of herbs in a northern hardwood forest.   Botanical Gazette 139: 467-481.

Melaas, E.K., D. Sulla-Menashe, and M.A. Friedl. 2018.  Multi-decadal changes in interannual variation in springtime phenology of North American temperate and boreal deciduous forests.  Geophysical Research Letters doi: 10.1002/2017GL076933

Miller-Rushing, A.J., R.B. Primack, D. Primack and S. Mukunda. 2006.  Photographs and herbarium specimens as tools to document phenological changes in response to global warming. American Journal of Botany 93: 1667-1674.

Primack, D., C. Imbres, R.B. Primack, A.J. Miller-Rushing, and  P. Del Tredici.  2004.  Herbarium specimens demonstrate earlier flowering times in response to warming in Boston.  American Journal of Botany 91: 1260-1264.

Vitale, J. and W.H. Schlesinger.  2011.  Historical analysis of the spring arrival of migratory birds to Dutchess County, New York:  A 123-year record.  Northeastern Naturalist 18:335-346.

Wang, H., J. Dai, T. Rutishauser, A. Gonsamo, C. Wu and Q. Ge. 2018.  Trends and variability in temperature sensitivity of lilac flowering phenology.  Journal of Geophysical Research-Biogeosciences doi: 10.1002/2017JG004181.

4 thoughts on “Phenology

  1. Bill:

    Here in upstate New York State along the northern border of Pennsylvania, it was 19 F. degrees this morning and we still have snow on the ground. Last year I was riding in a T-shirt in the woods at this time of year. The weathermen have predicted a foot of snow for NYC today and tomorrow, the fourth major nor’easter in the last 30 days or so. Our definition of nor’eastern in this part of New York State: “we won’t have warm weather at Ground Hog’s Day, nor Valentine’s Day, nor Easter. ”
    Here is little ditty we recite this time of year:

    Spring arrived today.
    This morning at one a.m.
    I awoke to the sound
    of geese overhead –
    honking northward.
    The first wave, I said
    or simply the first which I have heard?
    After that I slept.
    This morning on the radio
    I heard the temperature would rise to 65,
    I heard that it would rain today –
    I heard tomorrow that it would snow.
    Spring arrived today
    in a way,
    and tomorrow it will go.

    1. “What’s the difference between climate and weather?” [Steve] Colbert asks. “Is not climate just made up of thousands of little weathers?”

  2. Brian Chabot has some great data on the date and volume of sap flow in sugar maple. Big economic implications there.

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