About the Database

The “DFMorph” (Darwin’s Finch Morphology) database contains data, mostly morphological (e.g., beak dimensions), on individual Darwin’s finches. The data are from a number of published and unpublished sources.

Additional information includes the publication, source of the specimen, the original specific or subspecific name assigned by the author(s), museum location and catalog number, and other information of historical importance. In particular, Sulloway’s (1982) measurements of existing Beagle specimens have been included.

This version contains data from four sources. The first three were in BIRDD version 1, the last is new with version 2.

  • The largest published collection of measurements, taken from Snodgrass & Heller’s important early work (1904).
  • Sulloway’s historically significant examination of the history of all surviving finch specimens collected by members of the Beagle expedition (1982).
  • Measurements published in Swarth’s (1931) monograph.
  • Over 6,500 specimens that David Lack measured for his 1945 monograph and 1947 book. Lack deposited copies of his measurements in the British Museum (Natural History) and the California Academy of Sciences (CAS); we optioned copies of the latter from the CAS Archives. These more extensive data provide many opportunities for students to explore variation among individual finches and island populations, and to try to understand how taxonomists separate specimens into species and subspecies.

There is considerable overlap among these subsets of data. Some specimens, such as those of the Beagle expedition, may appear in all of them. The Dataset Choice field on the Table of Contents allows you to determine which set of data to examine and export.


Lack, D.L. (1945). “The Galápagos finches (Geospizinae): a study in variation.” Occasional Papers of the California Academy of Sciences 21: 1-159.

Lack, D.L. (1947). Darwin’s Finches: an essay on the general biological theory of evolution. Cambridge, England, Cambridge University Press.

Lack, D.L. (1969). “Subspecies and sympatry in Darwin’s Finches.” Evolution 23: 252-263.

Snodgrass, R. E. and E. Heller (1904). “Papers from the Hopkins-Stanford Galapagos Expedition, 1898-99 XVI. Birds.” Proc. Wash. Acad. Sci. 5: 231-372.

Sulloway, F. J. (1982). “The Beagle collections of Darwin’s Finches (Geospizinae).” Bulletin of the British Museum (Natural History), Zoology series 43: 49-94.

Swarth, H. S. (1931). “The avifauna of the Galapagos Islands.” Occ. Pap. Calif. Acad. Sci 18: 5-299.

Notes About the Data

Taxon Names and IDs

The initial confusion and debate over the classification of Darwin’s finches settled down in 1931 with Swarth’s monograph. Lack made relatively minor changes (1945, 1947, 1969) and with some exceptions, that is the system used by most modern workers. We have elected to use Lack’s 1969 classification as our standard. Lack’s names for genus and species names plus subspecies if appropriate are the “modern” taxa and are listed with “.L69” at the end of the field name. In addition, wherever possible we have also recorded the original author’s name. See references and notes in the Species database for more details.

Some of the taxonomic names are lengthy, so we also have a more compact Species.ID as well as a Subspecies.ID where necessary. The Species.ID is made up of the first 3 letters of Lack’s genus, a period, and the first 3 letters of Lack’s species name. For subspecies, a period and the first 3 letters of Lack’s subspecies name are added.

For example, the specimens of sharp beaked ground finches on Darwin/Culpepper have the following values:

Field Name Example Taxon
TaxonOrig Geospiza septentrionalis
TaxonL69 Geospiza difficilis septentrionalis
GenusL69 Geospiza
SpeciesL69 difficilis
SubspL69 septentrionalis
SpeciesID Geo.dif
SubspID Geo.dif.sep

Notes on Data Fields

The terms “beak” and “bill” are used interchangeably.

Here are notes on commonly used data and measurements. Specific definitions and procedures for that source’s data are described later. The following picture summarizes the various measurements.

Morphology Measurements

Morphology Measurements

Attribute      Database Field and Notes
Sex Sex
We coded as M, F or U for unknown; a few marked with “?” in originals were coded as the indicated with the appropriate letter plus “u” for “uncertain”, i.e., Mu and Fu.
Age Age
Several authors coded Adult and Juvenile and we had previously accepted their designation. However, most of those assignments were based on plumage and the assumption that for, Geospiza at least, black males were adult and “streaked” or “partially black” males were juvenile. This is now known to be incorrect, so we no longer export age information. (not included in dataset)
Plumage Plumage
Some authors designated Age as “black” or “streaked”; we put these designations into Plumage.
Wing Length WingL
Tail Length TailL
Culmen UBeakL
“Culmen” is the technical term; we use a more easily understood, if longer, term. Note that Lack measured culmen from beak tip “to where it joins the skull”, while Swarth measured “exposed culmen” beyond feathers.

Both of the above differ from “Nostril-to-Maxilla” (Snodgrass & Heller), “Culmen from Nostril” (Lack) and “Lip of nostril to tip of beak” (Sulloway). To avoid confusion, these latter are code in the Nostril-Upper.Beak.Length field.
Gonys LBeakL
Again, a technical term made more easily understood. The lower beak typically is shaped like a “Y”; the measurement is usually from the fork of the Y (throat) to the bottom (tip of beak).
Basal Width of Bill BeakW
Basal Depth of Bill BeakH
“Depth” may be interpreted as front–to–back length, so we use “height”.
Tarsus TarsusL
Length of “leg”. Actually, the majority of a bird’s leg is a single bone, the tibiotarsus, that extends from the “ankle” joint to the toes, or phalanges.
  • Sources used a variety of English island names; we display island names in our “Common / English” format.
  • All measurements are in millimeters.
  • There are a number of duplicate museum catalog numbers within the Snodgrass & Heller data, and between the S&H, Sulloway and Swarth data. The measurements of these birds typically differ because of inherent variability in the way measurements are are made (e.g., how much pressure is applied to a wing), as well as to differences in definitions of measurement (e.g., whether culmen is defined as from tip to feathers or from tip to skull). We have tried to note duplicates in the Notes field for each bird, but left the data as in the original tables.

Museum Abbreviations

Museum abbreviations (mostly used by sources):  
BM(NH) British Museum (Natural History)
Brit Mus: British Museum
UMZC: University Museum of Zoology, Cambridge
LRNH: Leiden Rijksmuseum van Natuurlijke Historie
Stanf. Univ. Mus. Stanford University Museum
Calif Acad Sci California Academy of Sciences
U S Nat Mus United States National Museum
W Johnson private collection of Captain W. Johnson, of San Francisco

Snodgrass & Heller (549 specimens)

  • Snodgrass & Heller used the following approach to designating subspecies: “Trinomials are applied according to A. O. U. canons of nomenclature, i.e., when forms overlap in their variations, regardless of the possibility or impossibility of their interbreeding, they are called subspecies.” (p. 234)
  • All measurements are in millimeters. (p. 235)
  • “Measurements of length are in all cases of the specimen before being skinned.” (p. 235) These measurements must thus have been made in the field and recorded in catalogs or on specimen catalogs. All other sources made measurements on dried specimens.

Swarth (75 specimens)

  • Swarth made all measurements himself, but did not repeat each measurement. He noted that “extremes were gone over several times.”
  • Age: Originally coded as “black” and “streaked”. We originally followed Swarth usage and coded “Adult” for black and “Juv” for streaked . We have left the data in the database, but no longer export age data (see “Age” in the table above.
  • Date: We recoded collection date from Mon. Day, Year format to mm/dd/year.
  • Wing Length: measured as the “straight line from bend of closed wing to tip of longest primary, with those feathers in their natural position (not straightened).” (p. 9) This may differ from Sulloway’s and Lack’s “flattened” measurement.
  • Tail Length: measured from “point of insertion of middle rectrices to tip of the longest.” (p. 9)
  • Culmen (Upper Beak Length): Measured in a straight line from a point where the feathers cease to hide the culmen, to tip of maxilla; the chord of the exposed culmen." (p. 9)
  • Depth of Bill at Base (Beak Height): measured from the “base of culmen to angle formed by feathers at lower edge of ramus of mandible.” (p. 9)
  • Width of Mandible (Beak Width): measured at “base of lower mandible.”(p. 9)
  • Tarsus (Tarsus Length): measured as a “straight line from center of heel joint on posterior side to joint between metatarsus and middle toe on anterior side.” (p. 9)
  • Middle toe with claw (Middle Toe Length; MToeL): measured “along upper side, from joint between metatarsus and middle toe to tip of claw.” (p. 9)
  • Swarth measured a small number of “the type series of Geospiza magnirostris in the British Museum” and these data are included. There has been considerable confusion over the exact collection locality of Darwin’s and other Beagle specimens (Sulloway, 1982), so those designations are enclosed in quotes and they should not be taken at face value. See Sulloway’s records for the best data on the Beagle collections.
  • Swarth provided a number of profiles of individual specimens, mostly natural size. These have been scanned and included in the dataon each finch.

Sulloway (51 specimens)

Sulloway has studied Darwin’s Galápagos collections and manuscripts and clarified many of the confusing points that confounded previous workers. In particular, Darwin neglected to record the localities where he collected his finches. Sulloway tracked down and measured all of the existing Beagle specimens and his (1982) paper is the best source of data on the Beagle finch collections.

Sulloway tried as much as possible to use Lack’s (1945) methodology in taking measurements:

  • Beak (bill) measurements were made with calipers accurate to better than 0.1 mm (less than typical range of error in making repeated measurements.
  • Each beak measurement was taken six times on the specimen’s right side; the high and low were discarded and the remaining four were averaged.
  • Culmen (Nostril-Upper Beak Length; N-UBkL): measured from superficial anterior lip of nostril to tip of bill.
  • Depth of Bill: measured from greatest height from base of bottom mandible to top of upper mandible before the curved culmen begins to descend (i.e., not where mandible meets skull). This may be different from those of other authors who were less specific about their procedures.
  • Wing Length: measurements were taken from both wings, when present, using a millimeter rule; the flattened wing was measured from carpal joint to tip of longest primary, to the nearest 0.5 mm. We report only the measurement of the right wing, unless that wing was missing., in which case we report the left wing.
  • Sulloway’s table reports both the island on the specimen’s label and his best determination from other sources (e.g., field notes, museum catalogues and specimen measurements). We report his best guess in the Island field and his full report in the record’s Note field. Sulloway presented the label’s locality first followed by a colon. Where an island name alone follows the colon, Sulloway determined locality on the basis of manuscript evidence. Where the colon is followed by “island form of subspecies”, the locality was estimated based on “the specimen’s measurements and plumage, which coincide with only one possible island form, given the various islands known to have been visited by the collector.

Lack (6,758 specimens)

David Lack’s monograph (1945) and book (1947) have had an enormous impact on evolutionary research and his illustrations have become icons in textbooks. The data in BIRDD are from a copy of his measurements deposited in the archives of the California Academy of Science.

Here are salient points on Lack’s methodology (1945):

  • Lack specifically tried to exclude specimens that had just left the nest, although he notes that it was impossible to determine whether they were sexually mature.
  • Lack doesn’t state whether he took multiple measurements and averaged them, as Sulloway did. It’s clear however that he tried to assess the reliability of his measurements (see notes below for the Culmen).
  • Beak measurements were made with dial calipers to nearest 0.1 mm.
  • Culmen (Upper Beak Length): measured from the tip of the bill to the place where the culmen joins the skull. This differed from Swarth’s approach and with several species Lack “was unable to estimate accurately the exact place where the culmen ended on the skull … measurements of the same specimens taken a month or two later sometimes gave different results.” (1945, p. 75). Unfortunately, Lack appears to have decided to stop collecting, or tabulating, this measurement. This reduces the comparability of his data with those of earlier workers.
  • Culmen-From-Nostril: The distance from the anterior edge of the nostril to the tip of the upper beak. This is the measurement that Lack (and Sulloway) decided to use in place of Swarth’s exposed culmen. In his published work Lack typically used “culmen” to refer to this measurement.
  • Bill Depth (Bill Height): measured at the base, with the bill closed. Some specimens had been stuffed with the bill slightly open and these were not measured.
  • Wing Length: measured from the carpal joint to the end of the longest primary in the flattened wing; measured with a millimeter rule to the nearest 1 mm. Note that Lack (and Sulloway) flattened the wing, while Swarth measured the “wing in natural position.”

Additional data

Attribute Database Field and Notes
Source of data Source
Short name of island IslandID