Habitat Conditions in the Singer TractPosted: November 15, 2014
Late last year, I wrote a post entitled “More Minutiae – Habitat Quality and Population Density in the Singer Tract”. I had to follow up with a couple of corrections and elaborations based on insights others shared with me. In the interest of providing more clarity and coherence, I thought I’d do a new piece combining the three posts and expanding on them a bit. I won’t delete the originals, but this one reflects what I think is a more accurate understanding of the material involved.
The initial post was inspired by the image above and the caption describing it as the “Third ivorybills’ nest”, one I had looked at but not closely until last year. When I did examine it carefully, I was struck by how open the surrounding area seemed to be. Then I started going through archival photographs and scrutinizing them a little more closely.
In browsing through the Louisiana Digital Library’s collection of Singer Tract photographs, I came across an image that I had missed, one of the bridge over John’s Bayou taken in 1940. Tanner (p.32) includes an ivorybill sighting from this immediate vicinity, just northwest of the bridge. What I find interesting about the photograph is that the forest along the road appears to be fairly even-aged and does not have the characteristics typically associated with old growth. It is similar to what can be found in many parts of Louisiana today. An image from along Sharkey Road taken in 1937 shows similar characteristics, although another shot from 1939 (probably taken east of the bridge) shows more impressive looking habitat.
Richard Pough wrote a follow-up report to the Audubon Society on the Singer Tract in 1944. It’s a very interesting document that raises some questions about Tanner’s work. Pough explicitly accepted “Tanner’s premises as to the feeding habits and habitat preferences of the ivory-bill”, but he also noted “[n]othing in Mr. Tanner’s study indicates that Ivory-billed Woodpeckers show any preference or marked dependence on trees of great size such as one would find only in a virgin forest. He found them doing 14% of their feeding on trees 3”-12” in diameter and 64% on trees under 24” in diameter.”
Pough pointed out that “Maps of the area as of 1846 showed much of the Tensas River in plantations and many cleared fields back from the river on some of the interior ridges. This development continued for another 20 years until the Civil War, by which time Madison Parish was producing 110,000 bales of cotton a year. As the Parish has never produced over 30,000 bales since the Civil War, one gets some idea of how much land is now occupied by second growth forest of approximately 80 years age.”
Pough found only one ivorybill, a female. He assumed, relying on Tanner, that this was the only one left in the Tract. He may well have been mistaken, since Gus Willett, game warden in the Tract, wrote Tanner about seeing a pair in November 1948 (although the exact location is unclear). Correction, Willett did not write the letter, although the report reached Tanner, as discussed here.
The lone bird Pough saw was either the John’s Bayou female or one of its offspring. According to Pough, this bird was probably not feeding in virgin forest, and his report specifically suggests that Tanner might have been mistaken about the maturity of some of the habitat in the John’s Bayou area. In 1941, Tanner had written that the remaining John’s Bayou birds were roosting and feeding in “virgin” timber. Pough’s description of this area (and it seems to be the same patch) suggests it was likely cultivated pre-Civil War. It was devoid of big sweet gums, which Pough deemed to be the best indicator of old growth conditions, but had many dying Nuttall oaks 12-20 inches in diameter. Nonetheless, Pough relied on Tanner’s premises to conclude that “only a relatively small portion of the total area of the Singer Tract supported a forest suitable as habitat for these birds.”
To return to the material in the earlier blog posts, much of the discussion focused on home ranges and the distribution of nest sites.
This map, drawn by Tanner after the 1935 expedition, lists three nests – designated as nests II, III, and IV –within a mile or two of each other and in the vicinity of John’s Bayou. Nest II is the famous “Elm Rock” nest. The map also shows a tree which is designated “Nest (?) III Squirrel” (also mentioned in Bales, “two miles to the south of the first nest” and fifty feet up p. 45). This was outside the area Tanner designated as prime in 1941 (p. 91); it is approximately a half-mile from the John’s Bayou bridge.
I’ve discussed this issue in depth with someone who’s very familiar with Tanner’s notes. I’m now persuaded Tanner concluded that nests III and IV from 1935 were not nests after all and that he assigned the birds involved to Titepaper (Nest III) and Bayou Despair (Nest IV). Nest IV is apparently one that Kuhn found but was unable to re-locate. Why Tanner changed his mind about it remains a mystery.
It’s very difficult to piece together this fragmentary information, and the monograph muddies the waters a bit by presenting the home ranges of the birds as being quite discreet, perhaps a good deal more than they were in fact. I suspect that Tanner decided the cavities were actually roosts, (although neither one is mentioned in the monograph). If so, they would have been well outside the home ranges Tanner identified and closer to the core of the John’s Bayou range than to the core of Titepaper or Bayou Despair.
Nests I and V were located near Mack’s Bayou. Nest I is dated May 14, ’34 on the map, and Nest V is dated May 10, ’35. The ’35 nest failed. It is the one referenced above. Allen and Kellogg described it as being 45’ feet up, in a pin oak snag, in a natural clearing, although it has been suggested that the snag may have been a remnant large tree in area that had been cleared prior to the Civil War. The nest designated Nest I and dated May 14, 1934 appears to be the one Tanner described on p. 81 of the monograph, “located within 100 yards of the second nest found in 1935”; however, in the monograph, he gave the date as May 13, 1933.
It’s worth pointing out that the Mack’s Bayou nests were in an area that Tanner designated as “best” for ivory bills (even if it’s not clear whether it was truly old growth). Nonetheless, nests failed in 1933 and 1935, and the adult birds had disappeared by 1938, apparently after producing one fledgling in 1936 or 1937. This was before the logging began.
My intention in writing those initial posts was to get a clearer handle on population densities and habitat requirements in the Singer Tract. In retrospect, I’m not sure that’s possible, since Tanner’s observations were almost entirely limited to one family of birds in a population that was dwindling for unknown reasons. At the very least, Tanner’s statement that 7 pairs of birds required 120 square miles of virgin forest in 1934 is based on an inflated estimate of the amount of old growth in the Tract and his minimum estimate of 6.25 square miles per pair also rests on that flawed premise.
Pough observed, “ . . . the ivorybill problem puzzles me exceedingly, and I do not feel that Tanner’s report begins to explain the reasons for the drastic decline in this species.” As the 2014-2015 search season approaches, I can only hope that the question of how the species persisted will puzzle people exceedingly in future years.