**2. Towards a new avian classification**

After Darwin, ornithologists overturned the typological species concept and tried to build up a "natural system", based on shared ancestry and comment descent. According to [6, 7], more than 40 classifications were proposed during the last two centuries. Since 1900, the order of bird families in handbooks and field guides was based on these classification systems [8–12].

Traditionally, morphology, such as plumage, beak and head shape, had been used to make inferences in systematics and taxonomy [1, 3]. Since 1900 new characters were included, coming from ecology, biogeography, and biochemistry. The main concept of classification remained overall similarity; the more similar two taxa, the more closely related they should be.

Whereas the inclusion of similar taxa into a common genus was mostly unambiguous, the circumscription of families and orders was however more difficult. In many taxa, a variation of plumage can be seen in relation to age, sex or season. Large skin collections were helpful to find out if the variable forms belonged to a single species. Several bird species (e.g. ducks and geese) can hybridize, which generate more confusion. We already noticed that adaptive characters can occur convergently. In consequence, similar adaptive features might have evolved in unrelated group of taxa. If such adaptive characters are used for taxonomy, artificial and polyphyletic groups (clades with members from unrelated lineages) may be created (**Figure 1**).

Over the last 200 years, different species concepts have also strongly influenced taxonomy and systematics [3, 4, 10]. Although ornithologists loved the typological species concept for a long time, it was substituted by Ernst Mayr by the Biological Species Concept (BSC). Presently, the "Phylogenetic Species Concept (PSC)" has been widely accepted, because it better fits the molecular data [1].

The German entomologist Willi Hennig (1913–1976) introduced the concept of cladistics. He distinguished plesiomorphic, apomorphic and synapomorphic traits

*Birds - Challenges and Opportunities for Business, Conservation and Research*

plants and animals were published. William Turner (1500–1568), Conrad Gessner (1516–1565), and Pierre Belon (1517–1564) were three known ornithologists in the 16th century. Gessner reported on 180 bird species in the illustrated *Historia animalium.* John Jonston (1603–1675) published the *Historiae naturalis de avibus libri VII* in 1650 illustrated by Matthaeus Merian (**Figure 1**). However, the classification was only based on morphology, leading to wrong relationships. As can be seen from **Figure 1**, bats were included in birds and the cuckoo and shrike were treated as

After 1600, the ornithological landscape quickly changed. New species were brought in from everywhere in the world by early explorers, and systematic collections of specimens were started facilitating the study of avian taxonomy. Known ornithologists of the 17th century were Walter Charleton (1619–1707), John Ray (1628–1704), and Francis Willughby (1635–1672). John Ray became famous since he produced with *Ornithologiae libri tres* a first modern ornithology handbook, based it

Another breakthrough came in the 18th century: Carl Linnaeus (1707–1778), a naturalist and medical doctor from Uppsala (Sweden) revolutionized taxonomy by introducing a binary nomenclature, in which every animal and plant species obtained its own and unequivocal Latin name [1–3]: The Chaffinch was called *Fringilla coelebs* L.; the first name indicates the genus and the second the species. This name is exclusive for the Chaffinch. By comparing the outer morphology of animals and plants, Linné arranged species with a similar anatomy and morphology into genera, orders and classes. For birds, Linné used the morphology of feet and beaks to distinguish six orders of birds, which included 85 genera. As there are several

*Illustrations from* Historiae naturalis de avibus libri VII*. As can be seen, shrikes and cuckoo were grouped with raptors because of their bill morphology. Cuckoo = Cuculus; shrike = Lanius; raptors = Tinnunculus, Dendrofalcus (a) and even bats were classified as birds because of their wings. Nycticorax= Night Heron;* 

*Caprimulgus = Nightjar; Bats= Fledermaus (b). (photo M. Wink).*

**4**

**Figure 1.**

raptors.

on authentic observations [4].

to define common ancestry in clades. Clades, which comprise all descendants of a common ancestor, are termed "monophyletic". According to cladistics, a natural system of classification should be only based on monophyletic groups. If scientists obtain evidence for para- and polyphyletic clades, taxa in such groups need to be either lumped or split until all clades are monophyletic. The consequences for bird taxonomy are discussed in Part 5.
