Flag that Bird Nest! (Reporting on Green Herons and their Boat-tailed Grackle Neighbors)
Dr. James J. S. Johnson
GREEN HERON nest: 1 hatchling, 3 unhatched eggs, parent AWOL!
(Jeffrey Pippins photograph)
Along a tidal creek at Port Lavaca, on the southeastern coast of Texas, on the west side of Lavaca Bay (where Hurricane Harvey storm-surged during August AD2017, with tidal flooding up to 6 feet deep), a “colonial” population of nesting Green Herons (Butorides virescens) was studied by Nate L. Trimble, for his M.S. thesis (AD2016, at Texas State University), with much of that study (co-authored by the M.S. committee chairman, M. Clay Green) being reported in last year’s issue of the BULLETIN OF THE TEXAS ORNITHOLOGICAL SOCIETY.
Most of that study focused on the nesting success (i.e., successful egg-laying, incubation, hatching, and fledging) of Green Heron babies, but one detail caught my eye (and is noted below), reminding me how birds think for themselves, sometimes in ways that ornithologists don’t expect.
But first, the context: the journal article’s abstract provides a contextual overview of the Green Heron study:
Green Herons (Butorides virescens) are small herons found throughout much of the United States and southwards into Mexico, Central America and the Caribbean. The species generally forages solitarily and often nests singly [i.e., in single pairs], with a breeding pair defending a breeding territory but sometimes form loose breeding colonies [i.e., neighborhood populations] presumably as a function of habitat availability and/or predator pressure.
We monitored a breeding colony of at least 35 Green Heron pairs along a tidal creek in Port Lavaca, Texas. Our study sought to examine the nesting ecology of colonial Green Herons and to investigate [mathematical] relationships between nest density, nearest neighbor distance and nest success. …
[Quoting Nate L. Trimble & M. Clay Green, “The Influence of Nearest Neighbor Spacing on Nesting Success of Green Herons (Butorides virescens) in Texas”, BULLETIN OF THE TEXAS ORNITHOLOGICAL SOCIETY, 51(1-2):32-41 (December 2018), at page 32.]
The habitat of these studied Green Herons, according to Trimble & Green is as follows:
The location of the breeding colony [of Green Herons] near Port Lavaca, is a treeless tidal wetland with the shrub Marsh Elder (Iva frutescens) lining the banks of a small tidal [saltmarsh] creek offshoot of the much wider Garcitas Creek near Port Lavaca [Texas]. These shrubs are utilized by the Green Herons for placement of their nests. Iva frutescens at this location ranges from 1-2 m[eters] in height and is the tallest foliage and the only woody vegetation in the immediate vicinity of the colony. This shrub has a relatively high tolerance to salinity, but a relatively low tolerance to flooding, causing it to grow in narrow bands in upper regions of salt marshes. … The shrub Iva frutescens was also utilized as nesting substrate for other birds in the vicinity of the Green Heron colony at Garcitas Creek, including … [Red-winged Blackbirds, Boat-tailed Grackles].
[Quoting Nate L. Trimble & M. Clay Green, “The Influence of Nearest Neighbor Spacing on Nesting Success of Green Herons (Butorides virescens) in Texas”, BULLETIN OF THE TEXAS ORNITHOLOGICAL SOCIETY, 51(1-2):32-41 (December 2018), at page 34.]
The Green Heron colony territory was visited by Boat-tailed Grackle (which are “conspecific” with the Great-tailed Grackle, — i.e., both grackle varieties hybridize, proving that they both descend from and belong to a common reproductive “kind” that God created on Day #5 of Creation Week), some of which preyed upon the Green Heron nest eggs, according to Trimble & Green [id., page 34].
In order to collect quantifiable data, the researchers needed to repeatedly observe the nest sites, to see if eggs were successfully laid and incubated, and to see if any of the hatchlings were successfully fledged.
In order to facilitate the data collection process (which covered the timeframes of April-August of AD2014 and April-July AD2015), the researchers needed to repeatedly monitor the heron nests, using boats, due to the logistics of accessing nests, amidst dense vegetation growing alongside the monitored creek area.
Observations were taken from a 3.5 m[eter] boat with an outboard motor [which may have frightened the birds, possibly skewing the reported observations]. All nest were marked with flagging.
[Quoting Nate L. Trimble & M. Clay Green, “The Influence of Nearest Neighbor Spacing on Nesting Success of Green Herons (Butorides virescens) in Texas”, BULLETIN OF THE TEXAS ORNITHOLOGICAL SOCIETY, 51(1-2):32-41 (December 2018), at page 35.]
Plastic flags, with numbers, are often used by ornithologists, to identify specific nests being investigation (which prevents accidental re-sampling of the same sites), although some ornithologists prefer to use quiet boats, poled in coastal waters, in order to avoid frightening the birds they are studying. [See, e.g., William Post & Carol A. Seals, “Bird Density and Productivity in an Impounded Cattail Marsh”, JOURNAL OF FIELD ORNITHOLOGY, 62(2):195-199 (spring 1991), at page 196. See also, e.g., William Post & Carol A. Seals, “Nesting Associations of Least Bitterns and Boat-tailed Grackles”, THE CONDOR, 95:139-144 (1993), at page 139.]
Flagging? Surely this would be a difficulty-free aspect in this habitat investigation.
However, birds will be birds – and God has gifted each birds with an animal “soul” (Hebrew: NEPHESH) with which it can think for itself! And so the researchers encountered a complication that they likely never planned for — birds with agendas of their own! This is casually noted in the report’s coverage of research challenges.
We were also unable to measure nearest neighbor estimates for some nests in 2015 because the flags were lost either to flooding or by grackles taking the flagging for nest material. There were four nests in which the nest and flag disappeared and could not be included in the analysis.
[Quoting Nate L. Trimble & M. Clay Green, “The Influence of Nearest Neighbor Spacing on Nesting Success of Green Herons (Butorides virescens) in Texas”, BULLETIN OF THE TEXAS ORNITHOLOGICAL SOCIETY, 51(1-2):32-41 (December 2018), at page 40.]
But why would these researchers suspect that grackles may have pilfered their nest-monitoring flags?
Grackles are famous for their eclectic approach to nest-building, sometimes incorporating cloth scraps, paper shreds (including toilet paper!), reeds, woody stems, horsehair, cattail material, bark strips, weds, plastic (including pieces of plastic bags), ribbons, flagging tape, feathers, mud, leaves, twigs, grass, string, bovine manure, and even corn husks! [See, accord, Cornell Lab of Ornithology, “Great-tailed Grackle”, posted at https://www.allaboutbirds.org/guide/Great-tailed_Grackle/lifehistory . See also, accord, Animal Diversity Web, “Quiscalus quiscalus Common Grackle”, posted at https://animaldiversity.org/accounts/Quiscalus_quiscula/ .]
Apparently, even saltmarsh-dwelling grackles like to have nests with a little “interior decorating” bling, such as the colorful accent provided by ornithologists’ plastic ribbon-like flags.