Joel Stebbins Determined Migrating Bird Heights Via Telescopes in 1905

Summary: American astronomer Joel Stebbins determined migrating bird heights via telescopes in 1905, according to his February 1906 report in Popular Astronomy.

Illustration shows May 19, 1905, path of eighth bird, as charted by Joel Stebbins (S8) and Frederic Carpenter (C8), with Stebbins sited 21 feet east of Carpenter; J. Stebbins, "A Method of Determining the Heights of Migrating Birds," Popular Astronomy (February 1906), page 66: Public Domain, via HathiTrust

American astronomer Joel Stebbins determined migrating bird heights via telescopes in 1905, according to his report in the February 1906 issue of Popular Astronomy.

During spring and autumn 1905, University of Illinois-Urbana astronomy professor and Astronomical Observatory director Joel Stebbins (July 30, 1878-March 16, 1966) teamed with University of Illinois-Urbana zoology professor Frederic Walton Carpenter (May 12, 1876-March 1, 1925) on a project to determine the heights achieved by migrating birds. The project took place on the grounds of the University of Illinois Observatory.

The duo's most successful observation sessions occurred on Friday, May 19, and Tuesday, October 10. Stebbins reported a total viewing of 78 separate birds within two and one-half hours on May 19. Carpenter recorded 34 birds, and Stebbins saw 33. Eleven birds were seen by both observers.

Within a two-hour period on Oct. 10, viewed birds totalled 57, with 11 recorded by both observers. Carpenter noted 29 birds while Stebbins espied 17.

The greatest range in avian altitude occurred on Oct. 10. Nine birds accounted for a variation of 1,400 to 5,400 feet. The greatest distance between any bird and the observers was 7,700 feet.

On May 19, the altitude of nine birds ranged from 1,200 to 2,400 feet. The greatest distance between the observers and any bird was 7,100 feet.

Error percentages were assigned to the altitude ranges for the two dates. The greatest height of 5,400 feet was deemed to have a possible error of 25 percent. Lower distances were considered to have a probable correctness of within 10 percent.

Stebbins noted the assumption held by previous observers of migratory bird height that altitudes of two to three miles or more were achievable. Contrarily, Stebbins and Carpenter experienced no heights of more than half a mile on May 19. The majority of that date's birds flew below 1,200 feet. While one or two birds flew "as high as a mile" on Oct. 10, most birds stayed below "1200 or 1500 feet" (page 70).

Stebbins and Carpenter's method entailed determining the parallax of each migrating bird. Parallax references the angle subtended by two sight-lines. They established the distance between their observation posts as the parallax's base line.

Stebbins and Carpenter used two small equatorial telescopes with different apertures. The four-inch aperture telescope was mounted on a fixed pier. The three-inch telescope was set on a movable tripod in order to allow for any direction or length for the base line of each bird's parallax. Experimentation revealed that a distance of 10 feet between observers established the best base line for lunar passage near the meridian, or the longitude of their location.

Placement of the telescopes at right angles to bird flight direction assured simplicity in observation and computation. Flight direction was established as northward in spring and southward in autumn. Specifically, Stebbins and Carpenter found in their observations that most birds averaged northwesterly flight in spring and southeasterly flight in autumn. The telescopes were sited on an east and west line.

Each telescope's eyepiece presented a power of about 25. Each eyepiece included all of the lunar disk within its field of view.

The placement of a reticle of four heavy crosshairs in the focal plane allowed for division of the field of view into octants. Rotation of the reticle continued until one of the crosshairs paralleled the moon's diurnal, or apparent daily, motion. During observation sessions, the intersection of the crosshairs centered on the circular arc of the lunar image. A bird's path was estimated from different crosshairs. Stebbins and Carpenter found that best observations usually occurred in the latter part of a bird's path across the lunar disk.

Stebbins noted that the observations conducted by Carpenter and himself apparently marked the first instance of usage of "this simple method" in determining migratory bird heights. He concluded that practice of the method at "many stations over the country" would yield valuable nocturnal flight data for ornithologists.

The takeaway for Joel Stebbins' determination of migrating bird heights via telescopes in 1905 is that the University of Illinois astronomy professor devised and tested, in collaboration with University of Illinois zoology professor Frederic Walton Carpenter, a method for calculating migrating bird heights, against the bright backdrop of the lunar disk, by establishing each bird's parallactic angle via two telescopes stationed 10 feet apart.

Illustration shows angles, axes and planes for computing migrating bird height, with B=bird, H=bird's height above ground, O=observer on east-west line, W=west, x=east, y=north; J. Stebbins, "A Method of Determining the Heights of Migrating Birds," Popular Astronomy (February 1906), page 68: Public Domain, via HathiTrust

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

Illustration shows May 19, 1905, path of eighth bird, as charted by Joel Stebbins (S8) and Frederic Carpenter (C8), with Stebbins sited 21 feet east of Carpenter; J. Stebbins, "A Method of Determining the Heights of Migrating Birds," Popular Astronomy (February 1906), page 66: Public Domain, via HathiTrust @ https://hdl.handle.net/2027/njp.32101075380152?urlappend=%3Bseq=96

Illustration shows angles, axes and planes for computing migrating bird height, with B=bird, H=bird's height above ground, O=observer on east-west line, W=west, x=east, y=north; J. Stebbins, "A Method of Determining the Heights of Migrating Birds," Popular Astronomy (February 1906), page 68: Public Domain, via HathiTrust @ https://hdl.handle.net/2027/njp.32101075380152?urlappend=%3Bseq=98

For further information:

Abbott, David. The Biographical Dictionary of Scientists: Astronomers. New York NY: Peter Bedrick Books, 1984.

Carpenter, Frederic W. "An Astronomical Determination of the Heights of Birds During Nocturnal Migration." The Auk, vol. 23, no. 2 (Apr., 1906): 210-217.
Available via JSTOR @ https://www.jstor.org/stable/4070753

"Carpenter, Frederic Walton." The National Cyclcopaedia of American Biography, vol. XX: 322-323. New York: James T. White & Company, 1929. Available via HathiTrust @ https://hdl.handle.net/2027/mdp.39015078229088?urlappend=%3Bseq=708

Consolmagno, Guy; and Dan M. Davis. Turn Left at Orion. Fourth edition. Cambridge UK; New York NY: Cambridge University Press, 2011.

Levy, David H. Skywatching. Revised and updated. San Francisco CA: Fog City Press, 1994.

Marriner, Derdriu. "American Astronomer Joel Stebbins Pioneered Photoelectric Photometry." Earth and Space News. Wednesday, July 30, 2014.
Available @ https://earth-and-space-news.blogspot.com/2014/07/american-astronomer-joel-stebbins.html

Marriner, Derdriu. "Far Side Lunar Crater System Stebbins Honors American Astronomer Joel Stebbins." Earth and Space News. Wednesday, July 24, 2019.
Available @ https://earth-and-space-news.blogspot.com/2019/07/far-side-lunar-crater-system-stebbins.html

Marriner, Derdriu. "Joel Stebbins Observed Linné Crater During Feb. 8, 1906, Lunar Eclipse." Earth and Space News. Wednesday, Jan. 27, 2021.
Available @ https://earth-and-space-news.blogspot.com/2021/01/joel-stebbins-observed-linne-crater.html

Moore, Patrick, Sir. Astronomy Encyclopedia: An A-Z Guide to the Universe. New York NY: Oxford University Press, Inc., 2002.

Moore, Patrick, Sir. Philip’s Atlas of the Universe. Revised edition. London UK: Philip’s, 2005.

Scott, W.E.D. "Some Observations on the Migration of Birds." Bulletin of the Nuttall Ornithological Club, vol. VI, no. 2 (April 1881): 97-100. Cambridge MA: Nuttall Ornithological Club, 1881.
Available @ https://books.google.com/books?id=h3sVAAAAYAAJ

Stebbins, Joel. "A Method of Determining the Heights of Migrating Birds." Popular Astronomy, vol. XIV, no. 2, whole no. 132 (February 1906): 65-70.
Available via Harvard ADSABS (NASA Astrophysics Data System Abstracts) @ http://adsabs.harvard.edu/full/1906PA.....14...65S
Available via Harvard ADSABS (NASA Astrophysics Data System Abstracts) @ http://adsabs.harvard.edu/pdf/1906PA.....14...65S
Available via HathiTrust @ https://hdl.handle.net/2027/njp.32101075380152?urlappend=%3Bseq=95

Stebbins, Joel; and Edward A. Fath. "The Use of Astronomical Telescopes in Determining the Speeds of Migrating Birds." Science, vol. 24, issue 602 (July 13, 1906): 49-51.
Available @ https://science.sciencemag.org/content/24/602/49

Very, Frank W. "Observations of the Passage of Migrating Birds Across the Lunar Disk on the Nights of September 23 and 24, 1896." Science New Series, Vol. 6, No. 141 (Sep. 10, 1897), pp. 409-411.
Available via JSTOR @ https://www.jstor.org/stable/1625184