Good Trees Gone Bad

The cautionary Callery pear tale was covered in depth in a previous BYGL Alert titled, “Callery Pear: the Jekyll and Hyde Tree” (March 30, 2020). You can read the Alert by clicking on this hotlink: https://bygl.osu.edu/index.php/node/1476

The CliffsNotes® version goes like this. The specific epithet, calleryana, is in honor of a French missionary, Joseph Callery, who first collected the tree in 1858 in China. Unlike many members of the Rosaceae family, the tree showed remarkable resistance to infections by the bacterium behind Bacterial Fire Blight, Erwinia amylovora. The disease wreaked havoc on the common fruiting pear (P. communis).

Efforts were made by the USDA to tap into the Callery pear genetic secret sauce to impart resistance to fruiting pears. The breeding efforts failed to produce a fire-blight-resistant pear for orchards. However, one selection, with its snowy white flowers, lustrous green leaves, and glossy red fall color, showed value as a woody ornamental. The cultivar was named ‘Bradford’ in honor of Frederick Charles Bradford who was the director of the USDA Plant Introduction Station in Glenn Dale, Maryland.

The icing on the pear cake was that ‘Bradford’ was tolerant of bacterial fire blight with infections seldom progressing beyond the fruit spurs. Even better, it was genetically self-incompatible meaning trees wouldn’t produce a bunch of little Bradfords.

‘Bradford’ Callery pears eventually revealed their Achilles heel which was a weak branch structure. Some called them ‘Splitting’ Callery pears. However, in an early manifestation of "we have an app for that," plant breeders developed cultivars with better branch structures such as 'Aristocrat' and 'Cleveland Select' (a.k.a. 'Chanticleer').

Soon, there was a Callery pear for almost every occasion with 29 different cultivated varieties. We slept soundly in the knowledge that they were all well-behaved; they could not spread on their own.

Of course, as Jeff Goldblum in the form of Dr. Ian Malcolm observed, “life, uh… finds a way.” While ‘Bradford’, if left alone, was self-incompatible, the ever-expanding selections did not get the memo. Soon, we began seeing trees, including ‘Bradford’, bearing heavy fruit. We at first considered the fruit production to be nothing more than an oddity. “Yeah. "Ooh, ahh," that's how it always starts. But then later there's running and screaming.”

The first that I noticed something was going wrong was when trees with snowy white flowers began to appear in huge numbers in locations where they had not been planted such as the 13+ acre “field of pears” shown in the image below. This was not an abandoned nursery; none of the Callery pears were planted.

Although fall colors displayed by many deciduous trees are beginning to fade, Callery pears continue to blaze with the show-stopping colors that made us love them in the first place. Interestingly, the timing of fall color development, as well as leaf drop, varies widely among the “escaped” Callery pears which reflect genetic variability among the uncultivated cultivars.

The variability is demonstrated in the following images. The first image shows three Callery pears that were planted in front of a dense collection of feral pears. Note that the planted pears have already shed their leaves. The second image shows a group of escaped pears with one tree still retaining green leaves.

Unfortunately, as with vast expanses of white blooms in the spring, fall colors are also revealing the extent of Callery pear encroachment across Ohio. The image below shows a sea of undomesticated Callery pear seedlings adorned in fall finery covering multiple acres in a field in the southwest part of the state.

Of course, once spring blooms and fall colors made it abundantly evident that the crossing cultivars were running rampant across Ohio, a question began to emerge. How were the Callery pears spreading? The answer, my friend, isn’t blowin' in the wind. Although fruit sizes range widely on the wild Callery pears, it’s unlikely that even the smallest fruit could be spread far and wide by winds short of hurricane force.

A Bird in Hand is Worth Hundreds of Pears in the Bush

The cautionary European starling tale was covered in depth in a previous BYGL Alert titled, “Mesmerizing Murmuration” (December 16, 2021). You can read the Alert by clicking on this hotlink: https://bygl.osu.edu/node/1904

The airborne acrobatics by European starlings are known as a murmuration. It’s one of Nature’s most fascinating spectacles with thousands of starlings twisting, turning, swooping, and swirling in a synchronized close-formation aerial display.

The cloud-like black masses of huge numbers of starlings make murmurations appear as a single organism rather than a group of individuals. It’s a stunning example of collective animal behavior.

Although murmurations are most commonly observed in the fall, they may occasionally occur in the spring. Organized flights may arise spontaneously anytime during daylight hours; however, the most dramatic displays occur during the evening hours.

I posted a YouTube video in 2021 of starling murmurations and although the display is not nearly as dramatic as other online postings of this bizarre phenomenon, you can view the video by clicking this hotlink:

https://youtu.be/i4QDmpDatlk

Teresa Culley (Professor, Biological Sciences, University of Cincinnati) and Nicole Hardiman (U.C., Ph.D. Thesis) published the earliest work untangling exactly what was happening with the misbehaving Callery pears (see Selected References below). They noted that European starlings would feast on the fruit.

In 2022, Olivia Clark (University of Dayton) produced a fascinating honors thesis titled, “A Starling in a Pear Tree: Assessing the Influence of Bird Dispersal on Callery Pear (Pyrus calleryana)", (see Selected References below). Likewise, she noted that European starlings are among the most common birds observed eating Calley pear fruit. She also reported that other birds will eat the fruit including American Robins (Turdus migratorius, family Turdidae) as well as Cedar Waxwings (Bombycilla cedrorum, family Bombycillidae).

However, as Clark noted in her thesis, sheer numbers point towards the intestinal tract of European starlings as being a primary distribution route for Callery pears. Research published in 2017 showed that starling murmurations could include over 30,000 individuals.

I’m not suggesting robins or cedar waxwings aren’t responsible for spreading Callery pear seeds. However, I’ve never observed either of these species winging their way around Ohio in flocks numbering in the thousands.

Of course, the proof is in the pooping. Starling murmurations commonly occur shortly before the birds roost for the night and they frequently roost on power lines.

I’ve also observed that it’s common for starlings to lighten their load as they take flight as well as when they settle in for the night. Note the power lines above the “targeted” cars in the picture below.

The next images show the full extent of the starling “poop strafing.” The coloration and consistency of the starling deposits are consistent with Callery pear fruit. According to the literature, each fruit may contain 2 – 10 seeds.

The literature also notes that digestive juices in a bird's gut act to stratify seeds enhancing successful germination. It’s a small leap to conclude that the images shown in this Alert represent a potentially significant bird-assisted spread of Callery pears.

The Enduring Mythical Starling Origin Story

Much has been written about how European starlings found their way into North America. Unfortunately, important details are sometimes modified, fabricated, or outright omitted to suit certain narratives.

The most common and enduring myth is that Eugene Schieffelin is responsible for all of the European starlings currently pooping out nascent Callery pears across Ohio. Avian lore holds that Schieffelin was a rabid Shakespearian enthusiast who, with the aid of the nefarious American Acclimatization Society, hatched a plan to introduce all of the birds mentioned in Shakespeare's plays into North America. He started by releasing either 60 or 100 European starlings in Central Park in New York City, or so the stories go. However, it’s fake news.

Fugate and Miller (2021, see Selected References below) cast serious doubt on the often-repeated stories that there are direct connections between European starlings, Shakespeare, Schieffelin, and the American Acclimatization Society.

They claim there is little evidence that Schieffelin played a significant role in the overall success of starlings in the U.S. and his often-claimed obsession with Shakespeare is a complete fabrication. Thus, there is no evidence he had a goal of releasing every bird mentioned by Shakespeare.

Although Schieffelin was involved with releasing starlings into New York City’s Central Park in 1890 and 1891, these were not the first releases of starlings in North America. In fact, they were among the last. Releases had been going on in locations from Ohio to Oregon for decades before starlings were released in Central Park.

Indeed, Fugate and Miller cite as an example the releases of thousands of European birds including starlings in Cincinnati between 1872 and 1874 by the Society of the Acclimatization of Birds. The birds were imported and released to combat an outbreak of tree-defoliating caterpillars. No one was quoting Shakespeare when the cages were opened.

Understanding the goals of various "Acclimatization Societies" may be key to unraveling the tenuous link between starlings in the U.S. and Shakespeare. These societies were largely populated by European transplants to the U.S. They were most familiar with European flora and fauna but much less familiar with the ecological value of plants and animals native to North America.

One of the well-meaning goals of the societies was to import European flora and fauna to benefit agriculture in the U.S. such as the release of birds in Cincinnati to gobble up caterpillars. Another reported goal by these Societies across the U.S. was to introduce European animals and plants that were familiar to European ex-pats.

Of course, given that Shakespeare was based in Europe, it stands to reason that the societies would cast their bird-importing eyes on many of the same birds mentioned by Shakespeare including starlings. Thus, the supposed connection may be nothing more than a coincidence. Besides, although Shakespeare mentions 66 different species of birds in his plays and poetry, he only mentions starlings once.

Sadly, Eugene Schieffelin continues to play the Bogeyman in the starling origin story. Click on the hotlink below to his “Find a Grave” webpage and read the summary of his life as well as the snarky “Latest Memories of Eugene Schieffelin.”

https://www.findagrave.com/memorial/57547581/eugene-schieffelin

Selected References

Culley, T.M. and N.A. Hardiman. 2007. The beginning of a new invasive plant: a history of the ornamental Callery pear in the United States. BioScience, 57(11), pp.956-964. Available at:

https://www.researchgate.net/publication/232682928_The_Beginning_of_a_New_Invasive_Plant_A_History_of_the_Ornamental_Callery_Pear_in_the_United_States

Culley, T.M. and N.A. Hardiman. 2009. The role of intraspecific hybridization in the evolution of invasiveness: a case study of the ornamental pear tree Pyrus calleryana. Biological Invasions, 11, pp.1107-1119. Available at:

https://www.researchgate.net/publication/225322280_The_role_of_intraspecific_hybridization_in_the_evolution_of_invasiveness_A_case_study_of_the_ornamental_pear_tree_Pyrus_calleryana

Cavagna, A., A. Cimarelli, I. Giardina, G. Parisi, R. Santagati, F. Stefanini, and M. Viale. 2010. Scale-free correlations in starling flocks. Proceedings of the National Academy of Sciences of the United States of America, 107(26), 11865–11870. Available at: https://www.pnas.org/doi/full/10.1073/pnas.1005766107

Cavagna, A., S. M. Duarte Queirós, I. Giardina, F. Stefanini, and M. Viale. 2013. Diffusion of Individual Birds in Starling Flocks. Proceedings: Biological Sciences 280, no. 1756: 1–9. Available at: https://royalsocietypublishing.org/doi/full/10.1098/rspb.2012.2484

Daniel J. G. Pearce, Adam M. Miller, George Rowlands, Matthew S. Turner. 2014.

Role of projection in the control of bird flocks. Proceedings of the National Academy of Sciences, 111 (29) 10422-10426. Available at: https://www.pnas.org/doi/full/10.1073/pnas.1402202111

Goodenough A.E., N. Little, W.S. Carpenter, and A.G. Hart. 2017. Birds of a feather flock together: Insights into starling murmuration behaviour revealed using citizen science. PLoS ONE 12(6): e0179277. Available at: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0179277

Storms RF, C. Carere, F. Zoratto, and C.K. Hemelrijk. 2019. Complex patterns of collective escape in starling flocks under predation. Behav Ecol Sociobiol.;73(1):1-10. Available at: http://dx.doi.org/10.1007/s00265-018-2609-0

Fugate, L., and J. M. Miller. 2021. Shakespeare’s Starlings: Literary History and the Fictions of Invasiveness. Environmental Humanities 13, no. 2: 301-322. Available at:

https://read.dukeupress.edu/environmental-humanities/article/13/2/301/234995

Clark, O. 2022. A Starling in a Pear Tree: Assessing the Influence of Bird Dispersal on Callery Pear (Pyrus calleryana). University of Dayton, Honors Theses. 347. Available at:

https://ecommons.udayton.edu/uhp_theses/347/