June Insect Phenology

by Carl Strang

As I described in the previous post, plant phenology this year has been marching along in its usual pattern of between-year convergence of first flower dates. The results for insects in June were less consistent, and therefore more interesting. First appearance dates of 17 insect species in June were a median 11 days later in 2013 than in 2012. This is not surprising, given last year’s early season. There was some convergence, as that difference was 33 days in May.

The first sighting of Bombus auricomus at Mayslake Forest Preserve was on June 14 this year.

The first sighting of Bombus auricomus at Mayslake Forest Preserve was on June 14 this year.

No such convergence appeared in the comparisons of 2013 with 2011 and 2010, where the June median was 11 days later this year than in 2011 (19 species), and 9 days later than in 2010 (19 species). The differences in May were 10 days in each case, so no change. The median showed no difference (0 days) between June first appearances in 2013 and 2009 (19 species); in May that difference was 5 days.

The first monarch butterfly arrived from the South on June 13 (and yes, this is a photo from an earlier year).

The first monarch butterfly arrived from the South on June 13 (and yes, this is a photo from an earlier year).

We had some warm weather, but on the whole this spring was cool and often rainy. I think that weather pattern probably accounts for 2013’s continued lateness through June, and the relative lack of convergence to date.

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May Phenology 2: Insect First Appearances

by Carl Strang

Today’s seasonal comparison is between first appearance dates of insects at Mayslake Forest Preserve, through May. This includes April data, as there were not enough species in that month to consider alone.  As was the case with plants, the most dramatic difference was between this year and last: 15 species appeared a median 33 days later in 2013 than in 2012.

The differences from other years were smaller: 10 days later in 2013 than 2011 (15 species), likewise 10 days later than 2010 (13 species), and 5 days later than 2009 (12 species).

The bee fly Bombylius major first appeared 10 days later in 2013 than in 2010.

The bee fly Bombylius major first appeared 10 days later in 2013 than in 2010.

Green darners are our earliest dragonflies each year. In 2013 the first showed up 5 days later than in 2009.

Green darners are our earliest dragonflies each year. In 2013 the first showed up 5 days later than in 2009.

The numbers did not fully parallel those for flowering dates, in part because the months were combined, and in part because the sample sizes were smaller. Nevertheless, the 2013-2012 comparison is the consistent one. Also, this year is confirmed as the latest of the five I have been at Mayslake.

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.

First and Last Song Dates

by Carl Strang

I now have 7 years’ data in which I have noted the first and last dates on which I heard each singing insect species. This year was characterized by a mild winter followed by a warm spring and then a summer of drought. The mild winter and spring apparently were responsible for this year’s early phenology. First song dates were the earliest I have recorded in DuPage County for 17 of the 21 species for which I have 7 years of records. The chi-squared value of 77.33 (with an expected value of 3 species per cell for each rank of earliest to latest) is, of course, statistically significant.

The greater angle-wing started earlier and finished earlier this year than in any of the previous 6 years.

The greater angle-wing started earlier and finished earlier this year than in any of the previous 6 years.

As for last song dates, singing insects generally finished early this year. Of the 20 species for which I have 7 years’ data, 15 had their earliest or second-earliest ending dates, and the chi-squared value was a statistically significant 22.68. This was not a particularly cold or dry late summer and autumn, so the implication is that singing insects have a fixed rate of attrition or duration of song season, so that an early start results in an early finish. The 12 species for which I have the best, most reliable records do have differences in observed song season lengths (ranges for the 7 years, and ranked lowest to highest: 18-42 days for Roesel’s katydid, 16-52 days for gladiator meadow katydid, 52-96 days for the greater angle-wing, 58-96 days for snowy tree cricket, 67-91 days for the scissor-grinder cicada, 64-94 days for the greenstriped grasshopper, 62-109 days for Linne’s cicada, 72-105 days for the dog day cicada, 81-107 days for the common true katydid, 107-139 days for Allard’s ground cricket, 111-141 days for striped ground cricket, and 113-143 days for Carolina ground cricket).

The number of clear, cold nights seemed high enough in November that they might partly explain the early conclusion of common ground cricket songs this year, especially given the recent study by MacMillan et al. (2012) indicating that there is a metabolic cost to recovering from cold-temperature paralysis. However, I found no significant relationship between last song dates and the number of November days with low temperatures below 33F over 2006-2012 for any of the three species (Spearman’s r values 0.51 for Allard’s ground cricket, -0.39 for striped ground cricket, and 0.33 for Carolina ground cricket). It is interesting, though, that I have seen a few red-legged grasshoppers active a couple weeks after the last ground cricket.

An early December red-legged grasshopper

An early December red-legged grasshopper

This bigger insect may have larger fat reserves to draw upon and so extend its season.

July Insect Phenology

by Carl Strang

As detailed in the previous post, first flower dates were ahead of previous years by 1-1.5 weeks in July at Mayslake Forest Preserve. Insects also had been appearing early in previous months, but did this likewise continue?

In a word, yes. The 14 species I could compare between this year and last appeared a median 14 days earlier, continuing the trend (range 36 days earlier to 12 days later). The difference was only 4 days earlier than in 2010, however (15 species, range 46 days earlier to 14 days later). The largest difference was between 2012 and 2009, a median of 16.5 days earlier (14 species, range 4 to 36 days earlier). The respective differences in June were 22, 15.5 and 22 days, so there was some convergence in first appearance dates.

The black-legged meadow katydid was as representative as any species, beginning its singing 9 days earlier than in 2011, 4 days earlier than in 2010, and 18 days earlier than in 2009.

In this year of odd weather I do not know what to expect from the data for August.

June Insect Phenology

by Carl Strang

Insects, like plants, continue to reflect an early phenology this year. First appearances of insect species in June at Mayslake Forest Preserve were a median 22 days earlier than last year (13 species, range 66 days earlier to 46 days later). As was true for first flower dates, the difference was less extreme between 2012 and 2010, with a median of 15.5 days earlier this year for 14 species, ranging 48 days earlier to 62 days later.

The reversed haploa was close to the median values, appearing 22 days earlier than last year and 2009, 7 days earlier than in 2010.

The median difference was back to 22 days relative to 2009, ranging 80 days earlier to 31 days later for 13 species.

Early Singing Insects

by Carl Strang

To this point in the season I have heard singing males of 10 insect species in northeast Illinois. All but one began earlier than in any of the years from 2006 to 2011. This is consistent with more general insect phenology this year, and is attributable to a mild winter and a warm March which heated the soil earlier than usual. The only species with a later starting date was the spring field cricket, a species I usually hear first while running or bike riding, activities my back trouble prevented during the critical time period. And yet, despite that limited mobility, I have recorded dates for the other 9 species that ranged 5-22 days earlier than in any previous year (4 of the previous records were in 2007, 5 in 2010, 1 last year; they add up to 10 because of a tie). The only other case perhaps worth singling out was the broad-winged bush katydid, 22 days earlier than last year’s previous record. This species is not abundant or widely distributed, and I suspect it has a longer, earlier season than I have realized before. I should make some effort in future years to get a better handle on its starting and ending dates.

Broad-winged bush katydid

For those who may be interested, here are all the first song dates this year so far. Greenstriped grasshopper 3 April, 17 days earlier than the previous record. Spring field cricket 25 May, 20 days later. Roesel’s katydid 29 May, 11 days earlier. Protean shieldback 5 June, 7 days earlier. Linne’s cicada 14 June, 12 days earlier. Gladiator meadow katydid 14 June, 7 days earlier. Dog day cicada 15 June, 5 days earlier. Scissor-grinder cicada 19 June, 13 days earlier. Broad-winged bush katydid 23 June, 22 days earlier. Lyric cicada 24 June, 6 days earlier.

May Insect Phenology

by Carl Strang

As was the case with flowering phenology, insect species that first appeared in May did so earlier than in recent years at Mayslake Forest Preserve. The median difference between this year and last was 14.5 days earlier for 18 species, with a range of 86 days earlier to 5 days later. The median difference between 2012 and 2011 was less, at 8 days earlier for 15 species, ranging 21 days earlier to 46 days later. The difference was larger again with respect to 2009, a median of 16.5 days earlier for 14 species, ranging 95 days earlier to 46 days later.

Many of the early species were dragonflies, possibly finishing their development more quickly as waters warmed early this year. The first blue dasher appeared 9 days earlier than last year, 21 days earlier than in 2010, and 14 days earlier than in 2009.

With soil warming and plants growing so much more quickly, it is no surprise that plant-eating insects also were represented among the early species.

I saw the first least skipper on May 22 this year, June 8 last year, June 10 in 2010 and June 2 in 2009.

A third category was migrants, with the monarch butterfly being the iconic species here.

The first monarch arrived on May 4 this year, May 11 last year, May 19 in 2010 and May 26 in 2009.

Though local conditions would not have brought migrants here sooner, much of the U.S. had an early spring which could translate into quicker development of the offspring of those monarch migrants that overwintered in Mexico.

Insect First Appearances in April

by Carl Strang

In the previous post I shared data from Mayslake Forest Preserve showing that plants are continuing to bloom 2-4 weeks earlier than in the previous 3 years. Insects that made their first appearances in April likewise were ahead of 2009-2011.

The eastern forktail was representative, appearing 35 days earlier than in 2009, 41 days earlier than in 2010, and 34 days earlier than last year.

Sample sizes were small, though, with only 7 species to compare between each pair of years. The median difference between 2012 and 2009 was 43 days earlier (range 169 days earlier to 25 days later). The median was 41 days earlier than in 2010 (range 110 days earlier to 24 days later), and 35 days earlier than in 2011 (range 27 to 68 days earlier).

The first pearl crescent appeared on April 9 this year. That date was September 23 in 2009, July 2 in 2010 and May 12 last year.

These huge ranges may better be described as representing better survival for many species in the mild winter just past, so that there were more first-generation individuals, increasing the likelihood that I would see one. The pearl crescent could well be a case in point with respect to 2009 and 2010.

Insect First Appearances

by Carl Strang

Yesterday I detailed the phenology of first flowering dates at Mayslake Forest Preserve. Today I want to share some equally impressive first appearances of insect species there. Most of these observations were made in the warm period in mid-March.

Before this year I never had seen a common green darner earlier than April 2, anywhere in DuPage County. This year the first migrants showed up on March 19, and tandem pairs already were laying eggs in the stream corridor marsh.

One question in the back of my mind relates to the relatively mild but snow-free winter we experienced. Some species may have benefited from the warmer winter, but others may have been set back by the lack of insulating snow. One species that may have benefited is the spring azure. I have never seen so many of those little blue butterflies as I have counted already this year.

This year’s first sighting of a spring azure came 54 days earlier than last year, 23 days earlier than in 2010, and 21 days earlier than in 2009.

So, here are the statistics. Species counts are smaller than for the plants that bloomed in March, at 5-6 species per year. First appearances ranged 16 to 80 days earlier in 2012 than in 2011, with a median of 30.5 days earlier. The range for 2012 vs. 2010 was 17 to 36 days earlier, median 23 days earlier. The range for 2012 vs. 2009 was 21 to 40 days earlier, median 28 days earlier. These medians were similar to those for first flower dates, despite the smaller numbers of species.

Tomorrow I’ll conclude March’s remarkable phenology with migrant bird arrival dates.

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