Phenological Comparisons at a Site

by Carl Strang

Today I am sharing the first of two presentations I made on Saturday at the biennial Wild Things conference in Chicago, a popular event where the region’s restoration and natural history enthusiasts share information. This was a brief 15-minute talk on my phenological observations at Mayslake, which I have shared piecemeal in this blog over the years. Here I simply repeat the points and graphics from the PowerPoint projection.

Some generalizations:

  • Phenological comparisons are best done on a reasonably small site, so other variables are better controlled (Mayslake 90 acres).
  • However, on a small site some species will be uncommon, reducing year-to-year consistency.
  • This is compensated in part by including as many species as possible.

OLYMPUS DIGITAL CAMERA

Flowering phenology:

  • Flowering phenology is associated with soil temperature, so such factors as snow depth, severity of winter cold, and spring warmth are influential. 2012 had a warm spring following a mild, relatively snow-free winter, so flowering dates were unusually early.
  • As the season progresses, first flowering dates tend to converge between years.
First Flowering Dates, Mayslake Forest Preserve, Comparisons between Years Relative to 2012. The vertical axis gives the number of days median first flowering dates in each month were earlier in 2012 than in each of the other three years represented. For instance, in March 2012 flowers were appearing a median 32 days earlier than in 2009 and 2011, 21 days earlier than in 2010.

First Flowering Dates, Mayslake Forest Preserve, Comparisons between Years Relative to 2012. The vertical axis gives the number of days median first flowering dates in each month were earlier in 2012 than in each of the other three years represented. For instance, in March 2012 flowers were appearing a median 32 days earlier than in 2009 and 2011, 21 days earlier than in 2010.

Bee fly b

Insect phenology:

  • Insects mainly overwinter in the soil or under water, and so their first appearance phenology to some extent tracks that of first flowering dates.
  • Insects often have small first generations which can be missed, leading to large differences between years. Sample size helps, as well as intelligent data interpretation (knowing individual species’ natural history).
Insect Species First Appearance Dates, Mayslake Forest Preserve, Comparisons between Years Relative to 2012. This graph is set up just like the previous one. Note that the position of the “0” line, representing no difference in median dates in a month, is different from the first graph.

Insect Species First Appearance Dates, Mayslake Forest Preserve, Comparisons between Years Relative to 2012. This graph is set up just like the previous one. Note that the position of the “0” line, representing no difference in median dates in a month, is different from the first graph.

Baltimore oriole 4a

Migrant bird spring arrival phenology:

  • Bird phenology does not vary so much between years, especially for Neotropical migrants. Therefore, differences are greatest before the end of April.
Migrant Bird First Arrival Dates, Mayslake Forest Preserve, Comparisons between Years Relative to 2012. Graph set up like the first two.

Migrant Bird First Arrival Dates, Mayslake Forest Preserve, Comparisons between Years Relative to 2012. Graph set up like the first two.

Flower and insect phenology, influenced as they are by local winter and spring weather, follow parallel patterns with warmer years producing earlier flowering dates and insect appearances. Birds, coming from outside the area, are less subject to these influences though the birds that arrive earlier in the spring, coming from the southern U.S., may be experiencing similar weather and so respond accordingly. Neotropical migrants are unable to respond to such influences and so appear at close to the same dates each year, beginning in late April and early May.

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