Investigating little ornithological questions can lead to bigger things
Answering questions about birds is a gratifying part of my job as a curator. Answering my own questions maybe even better. But there are big questions like how did bird species diversity evolve? And there are small questions like is a single specimen correctly identified? There is a limited amount of time, so how should one prioritize? Bigger questions need to be the priority, but that does not mean that the smaller questions should be ignored because, when it comes down to it, those bigger questions always break down into series of smaller questions and sometimes, answering the small questions can take you to bigger questions you were not even thinking about.
As a doctoral student at Louisiana State University, I collected specimens in northeastern Bolivia for my dissertation research on genetic structure in relation to natural forest fragmentation. I did this fieldwork in conjunction with making a general, specimen-based inventory of the birds of Noel Kempff Mercado National Park. Over several years of work in the park, we documented many species in Bolivia for the first time. Among the many values of general collecting is that you may collect are things that you at first do not recognize. If you have a specimen and good data with it, you can go back later and make comparisons with specimens from other collections. During our Bolivian inventories, we collected a small female bird with a seed-eating bill that was plain dark brown all over. Female seedeaters (Sporophila) are notoriously hard to differentiate, so this specimen went without a name for quite a while, but I kept thinking about it.
The Serrania de Huanchaca in Parque Nacional Noel Kempff Mercado, Bolivia. The first record of Tiaris fuliginosa for Bolivia was collected in the humid forests at the base of the plateau.
One evening, while I was taking a break from writing my dissertation, I went up to the collection at LSU and was browsing through specimen drawers. In looking at this bird again, and comparing it to other specimens in the collection, I realized that it might not be a Sporophila at all, and that it appeared to instead be a Sooty Grassquit (Tiaris fuliginosa) which was yet another species new for Bolivia. Additional study verified this. So I had answered this small question about this one specimen (I should note that Van Remsen, LSU Curator of Birds had left a note in the drawer by this bird saying it looked most like Dull-colored Seedeater “Sporophila” obscura specimens from Colombia, so as you will see below,he was close). But in doing so, I opened up a window into many other questions that I was able to answer through examination of specimens of these birds in museum collections on three continents.
Here are some of the bigger (and littler) questions that were answered following identifying this one specimen to species.
1) Many specimens from throughout South America of what were called Sooty Grassquit (Tiaris fuliginosa) and Dull-colored Seedeater (Sporophila obscura) were misidentified.
2) These two species were actually each others’ closest relatives and belonged in the genus Tiaris (not Sporophila). I found this was supported by unpublished data others had noted on nest structure and recordings of songs, and the relationship was subsequently supported by DNA sequence data (including DNA sequences from LSUMZ #137740, our previously unidentified specimen).
3) Taken together, the ranges of these two grassquit species comprise a “circum-Amazonian” distribution pattern where a lineage of organisms is found in habitats all around the Amazon Basin, but not in Amazonia. We are still investigating how these ranges evolve and are maintained.
4) The southern populations (at least some of them) of Tiaris obscura appear to be migratory which may shed light onto the how migration evolves in birds.
5) In examining and often re-identifying specimens in other museum collections, I found the first record of T. obscura for Paraguay and the first record of T. obscura for Brazil. I found that all the published records of T. fuliginosa for Colombia were misidentified, but there were other unpublished specimens from Colombia that were T. fuliginosa.
6) With T. fuliginosa previous descriptions of different subspecies did not seem to hold up when one compared specimens. This species has a very patchy distribution, but that does not seem to have led to morphologically different populations.
7) Within T. obscura, there are five distinctive geographically separated populations through the Andes. With more study, several of these may be turn out to be best considered as species. One largely overlooked subspecies (T. o. pacifica) from coastal Peru may be endangered.
Three Tiaris specimens photographed by staff of the American Museum of Natural Hisotry. They were collected by H. H. Smith near Chapada, Mato Grosso, Brazil in 1885. All had long been considered to be T. fuliginosa. The male on the left is, but the other two upon comparison (they were collected in a different month), represent the first records of T. obscura for Brazil.
So, these findings still do not themselves answer the biggest questions in evolutionary biology, but in documenting new information and revising older information on these birds, they demonstrate why these species should be studied in greater detail with respect to broader questions associated with biogeography, behavior, and evolution. Not bad, stemming from finally clearing up the identity of a single little brown bird collected in the forests of eastern Bolivia.
Bates, J. M., M. C. Garvin, D. C. Schmitt, and C. G Schmitt. 1991. Notes on bird distribution in northeastern Dpto. Santa Cruz, Bolivia, with 15 new species to Bolivia. Bull. Brit. Orn. Club 109: 236-244.
Bates, J. M., T. A. Parker, III, A. P. Capparella and T. J. Davis. 1992. Observations on the campo, cerrado, and forest avifaunas of eastern Dpto. Santa Cruz, Bolivia, including 21 species new to the country. Bull. Brit. Orn. Club 112:86-98.
Bates, J. M. 1997. Distribution and geographic variation in three South American grassquits (Emberizinae, Tiaris). Ornithological Monographs 48:91-110.
Bates, J. M., D. F. Stotz, and T. S. Schulenberg. 1998. Avifauna of Parque Nacional Noel Kempff Mercado. Pp. 120-128. In: A Biological Assessment of Parque Nacional Noel Kempff Mercado, Bolivia. RAP Working papers 10. Conservation International, Washington, D. C.
Bates, J. M. and T. A. Parker, III. 1998. The avifauna of Parque Nacional Noel Kempff Mercado and surrounding areas. Pp. 317-340. In: A Biological Assessment of Parque Nacional Noel Kempff Mercado, Bolivia. RAP Working papers 10. Conservation International, Washington, D. C.
Bates, J. M. 2006. The seasonal movements of southern populations of Dull-colored Grassquit (Tiaris obscura obscura). Bull. Brit. Orn. Club 126:50-53.