Ornithology is a branch of zoology that concerns the
study of birds. Several aspects of ornithology differ from related
disciplines, due partly to the high visibility and the aesthetic appeal
of birds.
A marbled godwit being ringed for studies on bird
migration
A collection of bird skins
The science of ornithology has a long history and
studies on birds have helped develop several key concepts in evolution,
behaviour and ecology such as the definition of species, the process of
speciation, instinct, learning, ecological niches, guilds, island
biogeography, phylogeography, and conservation. While early ornithology
was principally concerned with descriptions and distributions of
species, ornithologists today seek answers to very specific questions,
often using birds as models to test hypotheses or predictions based on
theories. Most modern biological theories apply across taxonomic groups,
and the number of professional scientists who identify themselves as
"ornithologists" has therefore declined. A wide range of tools and
techniques is used in ornithology, both inside the laboratory and out in
the field, and innovations are constantly made.
The word "ornithology" comes from the late
16th-century Latin ornithologia meaning "bird science" from the Greek
ὄρνις ornis ("bird") and λόγος logos ("theory, science, thought").
History
The history of ornithology largely reflects the trends in the history of
biology, as well as many other scientific disciplines, including
ecology, anatomy, physiology, paleontology, and more recently, molecular
biology. Trends include the move from mere descriptions to the
identification of patterns, thus towards elucidating the processes that
produce these patterns.
Early knowledge and study
Humans have had an observational relationship with
birds since prehistory, with some stone-age drawings being amongst the
oldest indications of an interest in birds. Birds were perhaps important
as food sources, and bones of as many as 80 species have been found in
excavations of early Stone Age settlements.Waterbird and seabird remains
have also been found in shell mounds on the island of Oronsay off the
coast of Scotland.
Geese from a wall panel from the tomb of Nefermaat,
Egypt c. 2575–2551 B.C.
Cultures around the world have rich vocabularies
related to birds. Traditional bird names are often based on detailed
knowledge of the behaviour, with many names being onomatopoeic, and
still in use. Traditional knowledge may also involve the use of birds in
folk medicine and knowledge of these practices are passed on through
oral traditions (see ethno-ornithology). Hunting of wild birds as well
as their domestication would have required considerable knowledge of
their habits. Poultry farming and falconry were practised from early
times in many parts of the world. Artificial incubation of poultry was
practised in China around 246 BC and around at least 400 BC in Egypt.
The Egyptians also made use of birds in their hieroglyphic scripts, many
of which, though stylized, are still identifiable to species.
Early written records provide valuable information on
the past distributions of species. For instance, Xenophon records the
abundance of the ostrich in Assyria (Anabasis, i. 5); this subspecies
from Asia Minor is extinct and all extant ostrich races are today
restricted to Africa. Other old writings such as the Vedas (1500–800 BC)
demonstrate the careful observation of avian life histories and include
the earliest reference to the habit of brood parasitism by the Asian
koel (Eudynamys scolopacea). Like writing, the early art of China,
Japan, Persia, and India also demonstrate knowledge, with examples of
scientifically accurate bird illustrations.
Belon's comparison of birds and humans in his Book of
Birds, 1555
Aristotle in 350 BC in his Historia Animalium noted
the habit of bird migration, moulting, egg laying, and lifespans, as
well as compiling a list of 170 different bird species. However, he also
introduced and propagated several myths, such as the idea that swallows
hibernated in winter, although he noted that cranes migrated from the
steppes of Scythia to the marshes at the headwaters of the Nile. The
idea of swallow hibernation became so well established that even as late
as in 1878, Elliott Couescould list as many as 182 contemporary
publications dealing with the hibernation of swallows and little
published evidence to contradict the theory. Similar misconceptions
existed regarding the breeding of barnacle geese. Their nests had not
been seen, and they were believed to grow by transformations of goose
barnacles, an idea that became prevalent from around the 11th century
and noted by Bishop Giraldus Cambrensis (Gerald of Wales) in Topographia
Hiberniae (1187). Around 77 AD, Pliny the Elder described birds, among
other creatures, in his Historia Naturalis.
The earliest record of falconry comes from the reign
of Sargon II (722–705 BC) in Assyria. Falconry is thought to have made
its entry to Europe only after AD 400, brought in from the east after
invasions by the Huns and Alans. Starting from the eighth century,
numerous Arabic works on the subject and general ornithology were
written, as well as translations of the works of ancient writers from
Greek and Syriac. In the 12th and 13th centuries, crusades and conquest
had subjugated Islamic territories in southern Italy, central Spain, and
the Levant under European rule, and for the first time translations into
Latin of the great works of Arabic and Greek scholars were made with the
help of Jewish and Muslim scholars, especially in Toledo, which had
fallen into Christian hands in 1085 and whose libraries had escaped
destruction. Michael Scotus from Scotland made a Latin translation of
Aristotle's work on animals from Arabic here around 1215, which was
disseminated widely and was the first time in a millennium that this
foundational text on zoology became available to Europeans. Falconry was
popular in the Norman court in Sicily, and a number of works on the
subject were written in Palermo. Emperor Frederick II of Hohenstaufen
(1194–1250) learned about an falconry during his youth in Sicily and
later built up a menagerie and sponsored translations of Arabic texts,
among which the popular Arabic work known as the Liber Moaminus by an
unknown author which was translated into Latin by Theodore of Antioch
from Syria in 1240-1241 as the De Scientia Venandi per Aves, and also
Michael Scotus (who had removed to Palermo) translated Ibn Sīnā's Kitāb
al-Ḥayawān of 1027 for the Emperor, a commentary and scientific update
of Aristotle's work which was part of Ibn Sīnā's massive Kitāb al-Šifāʾ.
Frederick II eventually wrote his own treatise on falconry, the De arte
venandi cum avibus, in which he related his ornithological observations
and the results of the hunts and experiments his court enjoyed
performing.
Several early German and French scholars compiled old
works and conducted new research on birds. These included Guillaume
Rondelet, who described his observations in the Mediterranean, and
Pierre Belon, who described the fish and birds that he had seen in
France and the Levant. Belon's Book of Birds (1555) is a folio volume
with descriptions of some 200 species. His comparison of the skeleton of
humans and birds is considered as a landmark in comparative
anatomy.Volcher Coiter (1534–1576), a Dutch anatomist, made detailed
studies of the internal structures of birds and produced a
classification of birds, De Differentiis Avium(around 1572), that was
based on structure and habits. Konrad Gesner wrote the Vogelbuch and
Icones avium omnium around 1557. Like Gesner, Ulisse Aldrovandi, an
encyclopedic naturalist, began a 14-volume natural history with three
volumes on birds, entitled ornithologiae hoc est de avibus historiae
libri XII, which was published from 1599 to 1603. Aldrovandi showed
great interest in plants and animals, and his work included 3000
drawings of fruits, flowers, plants, and animals, published in 363
volumes. His Ornithology alone covers 2000 pages and included such
aspects as the chicken and poultry techniques. He used a number of
traits including behaviour, particularly bathing and dusting, to
classify bird groups.
William Turner's Historia Avium (History of Birds),
published at Cologne in 1544, was an early ornithological work from
England. He noted the commonness of kites in English cities where they
snatched food out of the hands of children. He included folk beliefs
such as those of anglers. Anglers believed that the osprey emptied their
fishponds and would kill them, mixing the flesh of the osprey into their
fish bait. Turner's work reflected the violent times in which he lived,
and stands in contrast to later works such as Gilbert White's The
Natural History and Antiquities of Selborne that were written in a
tranquil era.
Cover of Ulisse Aldrovandi's Ornithology, 1599
Antonio Valli da Todi, who wrote on aviculture in
1601, knew the connections between territory and song
In the 17th century, Francis Willughby (1635–1672) and John Ray
(1627–1705) came up with the first major system of bird classification
that was based on function and morphology rather than on form or
behaviour. Willughby's Ornithologiae libri tres (1676) completed by John
Ray is sometimes considered to mark the beginning of scientific
ornithology. Ray also worked on Ornithologia, which was published
posthumously in 1713 as Synopsis methodica avium et piscium. The
earliest list of British birds, Pinax Rerum Naturalium Britannicarum,
was written by Christopher Merrett in 1667, but authors such as John Ray
considered it of little value. Ray did, however, value the expertise of
the naturalist Sir Thomas Browne (1605–82), who not only answered his
queries on ornithological identification and nomenclature, but also
those of Willoughby and Merrett in letter correspondence. Browne himself
in his lifetime kept an eagle, owl, cormorant, bittern, and ostrich,
penned a tract on falconry, and introduced the words "incubation" and
"oviparous" into the English language.
An Experiment on a Bird in the Air Pump, Joseph Wright
of Derby, 1768
Towards the late 18th century, Mathurin Jacques
Brisson (1723–1806) and Comte de Buffon (1707–1788) began new works on
birds. Brisson produced a six-volume work Ornithologie in 1760 and
Buffon's included nine volumes (volumes 16–24) on birds Histoire
naturelle des oiseaux (1770–1785) in his work on science Histoire
naturelle générale et particulière (1749–1804). Jacob Temminck sponsored
François Le Vaillant [1753–1824] to collect bird specimens in Southern
Africa and Le Vaillant's six-volume Histoire naturelle des oiseaux
d'Afrique (1796–1808) included many non-African birds. His other bird
books produced in collaboration with the artist Barraband are considered
among the most valuable illustrated guides ever produced. Louis Jean
Pierre Vieillot (1748–1831) spent 10 years studying North American birds
and wrote the Histoire naturelle des oiseaux de l'Amerique
septentrionale (1807–1808?). Vieillot pioneered in the use of life
histories and habits in classification. Alexander Wilson composed a
nine-volume work, American Ornithology, published 1808-14—the first such
record of North American birds, significantly antedating Audubon. In the
early 19th century, Lewis and Clark studied and identified many birds in
the western United States. John James Audubon, born in 1785, observed
and painted birds in France and later in the Ohio and Mississippi
valleys. From 1827 to 1838, Audubon published The Birds of America,
which was engraved by Robert Havell, Sr.and his son Robert Havell, Jr.
Containing 435 engravings, it is often regarded as the greatest
ornithological work in history.
Scientific studies
The emergence of ornithology as a scientific
discipline began in the 18th century, when Mark Catesby published his
two-volume Natural History of Carolina, Florida, and the Bahama Islands,
a landmark work which included 220 hand-painted engravings and was the
basis for many of the species Carl Linnaeus described in the 1758
Systema Naturae. Linnaeus' work revolutionised bird taxonomy by
assigning every species a binomial name, categorising them into
different genera. However, ornithology did not emerge as a specialised
science until the Victorian era—with the concept of natural history, and
the collection of natural objects such as bird eggs and skins. This
specialization led to the formation in Britain of the British
Ornithologists' Union in 1858. In 1859, the members founded its journal
The Ibis. The sudden spurt in ornithology was also due in part to
colonialism. At 100 years later, in 1959, R. E. Moreau noted that
ornithology in this period was preoccupied with the geographical
distributions of various species of birds.
Early bird study focused on collectibles such as eggs
and nests.
No doubt the preoccupation with widely extended
geographical ornithology, was fostered by the immensity of the areas
over which British rule or influence stretched during the 19th century
and for some time afterwards.
— Moreau
The bird collectors of the Victorian era observed the
variations in bird forms and habits across geographic regions, noting
local specialization and variation in widespread species. The
collections of museums and private collectors grew with contributions
from various parts of the world. The naming of species with binomials
and the organization of birds into groups based on their similarities
became the main work of museum specialists. The variations in widespread
birds across geographical regions caused the introduction of trinomial
names.
Kaup's classification of the crow family
The search for patterns in the variations of birds
was attempted by many. Friedrich Wilhelm Joseph Schelling (1775–1854),
his student Johann Baptist von Spix (1781–1826), and several others
believed that a hidden and innate mathematical order existed in the
forms of birds. They believed that a "natural" classification was
available and superior to "artificial" ones. A particularly popular idea
was the Quinarian system popularised by Nicholas Aylward Vigors
(1785–1840), William Sharp Macleay (1792–1865), William Swainson, and
others. The idea was that nature followed a "rule of five" with five
groups nested hierarchically. Some had attempted a rule of four, but
Johann Jakob Kaup (1803–1873) insisted that the number five was special,
noting that other natural entities such as the senses also came in
fives. He followed this idea and demonstrated his view of the order
within the crow family. Where he failed to find five genera, he left a
blank insisting that a new genus would be found to fill these gaps.
These ideas were replaced by more complex "maps" of affinities in works
by Hugh Edwin Strickland and Alfred Russel Wallace. A major advance was
made by Max Fürbringer in 1888, who established a comprehensive
phylogeny of birds based on anatomy, morphology, distribution, and
biology. This was developed further by Hans Gadow and others.
The Galapagos finches were especially influential in
the development of Charles Darwin's theory of evolution. His
contemporary Alfred Russel Wallace also noted these variations and the
geographical separations between different forms leading to the study of
biogeography. Wallace was influenced by the work of Philip Lutley
Sclater on the distribution patterns of birds.
Quinarian system of bird classification by Swainson
For Darwin, the problem was how species arose from a
common ancestor, but he did not attempt to find rules for delineation of
species. The species problem was tackled by the ornithologist Ernst Mayr,
who was able to demonstrate that geographical isolation and the
accumulation of genetic differences led to the splitting of species.
Early ornithologists were preoccupied with matters of
species identification. Only systematics counted as true science and
field studies were considered inferior through much of the 19th century.
In 1901, Robert Ridgway wrote in the introduction to The Birds of North
and Middle America that:
There are two essentially different kinds of
ornithology: systematic or scientific, and popular. The former deals
with the structure and classification of birds, their synonymies, and
technical descriptions. The latter treats of their habits, songs,
nesting, and other facts pertaining to their life histories.
This early idea that the study of living birds was
merely recreation held sway until ecological theories became the
predominant focus of ornithological studies. The study of birds in their
habitats was particularly advanced in Germany with bird ringingstations
established as early as 1903. By the 1920s, the Journal für Ornithologie
included many papers on the behaviour, ecology, anatomy, and physiology,
many written by Erwin Stresemann. Stresemann changed the editorial
policy of the journal, leading both to a unification of field and
laboratory studies and a shift of research from museums to universities.
Ornithology in the United States continued to be dominated by museum
studies of morphological variations, species identities, and geographic
distributions, until it was influenced by Stresemann's student Ernst
Mayr. In Britain, some of the earliest ornithological works that used
the word ecology appeared in 1915. The Ibis, however, resisted the
introduction of these new methods of study, and no paper on ecology
appeared until 1943. The work of David Lack on population ecology was
pioneering. Newer quantitative approaches were introduced for the study
of ecology and behaviour, and this was not readily accepted. For
instance, Claud Ticehurst wrote:
Sometimes it seems that elaborate plans and
statistics are made to prove what is commonplace knowledge to the mere
collector, such as that hunting parties often travel more or less in
circles.
— Ticehurst
David Lack's studies on population ecology sought to
find the processes involved in the regulation of population based on the
evolution of optimal clutch sizes. He concluded that population was
regulated primarily by density-dependent controls, and also suggested
that natural selection produces life-history traits that maximize the
fitness of individuals. Others, such as Wynne-Edwards, interpreted
population regulation as a mechanism that aided the "species" rather
than individuals. This led to widespread and sometimes bitter debate on
what constituted the "unit of selection". Lack also pioneered the use of
many new tools for ornithological research, including the idea of using
radar to study bird migration.
Birds were also widely used in studies of the niche
hypothesis and Georgii Gause's competitive exclusion principle. Work on
resource partitioning and the structuring of bird communities through
competition were made by Robert MacArthur. Patterns of biodiversity also
became a topic of interest. Work on the relationship of the number of
species to area and its application in the study of island biogeography
was pioneered by E. O. Wilson and Robert MacArthur. These studies led to
the development of the discipline of landscape ecology.
A mounted specimen of a red-footed falcon
John Hurrell Crook studied the behaviour of
weaverbirds and demonstrated the links between ecological conditions,
behaviour, and social systems. Principles from economics were introduced
to the study of biology by Jerram L. Brown in his work on explaining
territorial behaviour. This led to more studies of behaviour that made
use of cost-benefit analyses. The rising interest in sociobiology also
led to a spurt of bird studies in this area.
The study of imprinting behaviour in ducks and geese
by Konrad Lorenz and the studies of instinct in herring gulls by
Nicolaas Tinbergen led to the establishment of the field of ethology.
The study of learning became an area of interest and the study of bird
songs has been a model for studies in neuroethology. The study of
hormones and physiology in the control of behaviour has also been aided
by bird models. These have helped in finding the proximate causes of
circadian and seasonal cycles. Studies on migration have attempted to
answer questions on the evolution of migration, orientation, and
navigation.
The growth of genetics and the rise of molecular
biology led to the application of the gene-centered view of evolution to
explain avian phenomena. Studies on kinship and altruism, such as
helpers, became of particular interest. The idea of inclusive fitnesswas
used to interpret observations on behaviour and life history, and birds
were widely used models for testing hypotheses based on theories
postulated by W. D. Hamilton and others.
The new tools of molecular biology changed the study
of bird systematics, which changed from being based on phenotype to the
underlying genotype. The use of techniques such as DNA-DNA hybridization
to study evolutionary relationships was pioneered by Charles Sibley and
Jon Edward Ahlquist, resulting in what is called the Sibley-Ahlquist
taxonomy. These early techniques have been replaced by newer ones based
on mitochondrial DNA sequences and molecular phylogeneticsapproaches
that make use of computational procedures for sequence alignment,
construction of phylogenetic trees, and calibration of molecular clocks
to infer evolutionary relationships. Molecular techniques are also
widely used in studies of avian population biology and ecology.
Rise to popularity
The use of field glasses or telescopes for bird
observation began in the 1820s and 1830s, with pioneers such as J.
Dovaston (who also pioneered in the use of bird feeders), but
instruction manuals did not begin to insist on the use of optical aids
such as "a first-class telescope" or "field glass" until the 1880s.
Page from an early field guide by Florence Augusta
Merriam Bailey
The rise of field guides for the identification of
birds was another major innovation. The early guides such as those of
Thomas Bewick (two volumes) and William Yarrell (three volumes) were
cumbersome, and mainly focused on identifying specimens in the hand. The
earliest of the new generation of field guides was prepared by Florence
Merriam, sister of Clinton Hart Merriam, the mammalogist. This was
published in 1887 in a series Hints to Audubon Workers:Fifty Birds and
How to Know Them in Grinnell's Audubon Magazine. These were followed by
new field guides including classics by Roger Tory Peterson.
The interest in birdwatching grew in popularity in
many parts of the world, and the possibility for amateurs to contribute
to biological studies was soon realized. As early as 1916, Julian Huxley
wrote a two-part article in The Auk, noting the tensions between
amateurs and professionals, and suggested the possibility that the "vast
army of bird lovers and bird watchers could begin providing the data
scientists needed to address the fundamental problems of biology."
Organizations were started in many countries, and
these grew rapidly in membership, most notable among them being the
Royal Society for the Protection of Birds (RSPB) in Britain and the
Audubon Society in the US, which started in 1885. Both these
organizations were started with the primary objective of conservation.
The RSPB, born in 1889, grew from a small group of women in Croydon, who
met regularly and called themselves the "Fur, Fin, and Feather Folk" and
who took a pledge "to refrain from wearing the feathers of any birds not
killed for the purpose of food, the ostrich only exempted." The
organization did not allow men as members initially, avenging a policy
of the British Ornithologists' Union to keep out women. Unlike the RSPB,
which was primarily conservation oriented, the British Trust for
Ornithology was started in 1933 with the aim of advancing ornithological
research. Members were often involved in collaborative ornithological
projects. These projects have resulted in atlases which detail the
distribution of bird species across Britain. In the United States, the
Breeding Bird Surveys, conducted by the US Geological Survey, have also
produced atlases with information on breeding densities and changes in
the density and distribution over time. Other volunteer collaborative
ornithology projects were subsequently established in other parts of the
world.
Techniques
The tools and techniques of ornithology are varied,
and new inventions and approaches are quickly incorporated. The
techniques may be broadly dealt under the categories of those that are
applicable to specimens and those that are used in the field, but the
classification is rough and many analysis techniques are usable both in
the laboratory and field or may require a combination of field and
laboratory techniques.
Collections
The earliest approaches to modern bird study involved
the collection of eggs, a practice known as oology. While collecting
became a pastime for many amateurs, the labels associated with these
early egg collections made them unreliable for the serious study of bird
breeding. To preserve eggs, a tiny hole was made and the contents
extracted. This technique became standard with the invention of the blow
drill around 1830. Egg collection is no longer popular; however,
historic museum collections have been of value in determining the
effects of pesticides such as DDT on physiology. Museum bird collections
continue to act as a resource for taxonomic studies.
Bird-preservation techniques
The use of bird skins to document species has been a
standard part of systematic ornithology. Bird skins are prepared by
retaining the key bones of the wings, legs, and skull along with the
skin and feathers. In the past, they were treated with arsenic to
prevent fungal and insect (mostly dermestid) attack. Arsenic, being
toxic, was replaced by less-toxic borax. Amateur and professional
collectors became familiar with these skinning techniques and started
sending in their skins to museums, some of them from distant locations.
This led to the formation of huge collections of bird skins in museums
in Europe and North America. Many private collections were also formed.
These became references for comparison of species, and the
ornithologists at these museums were able to compare species from
different locations, often places that they themselves never visited.
Morphometrics of these skins, particularly the lengths of the tarsus,
bill, tail, and wing became important in the descriptions of bird
species.
Morphometric measurements of birds are important in
systematics.
These skin collections have been used in more recent
times for studies on molecular phylogenetics by the extraction of
ancient DNA. The importance of type specimens in the description of
species make skin collections a vital resource for systematic
ornithology. However, with the rise of molecular techniques,
establishing the taxonomic status of new discoveries, such as the Bulo
Burti boubou (Laniarius liberatus, no longer a valid species) and the
Bugun liocichla (Liocichla bugunorum), using blood, DNA and feather
samples as the holotype material, has now become possible.
Other methods of preservation include the storage of
specimens in spirit. Such wet specimens have special value in
physiological and anatomical study, apart from providing better quality
of DNA for molecular studies. Freeze drying of specimens is another
technique that has the advantage of preserving stomach contents and
anatomy, although it tends to shrink, making it less reliable for
morphometrics.
In the field
The study of birds in the field was helped enormously
by improvements in optics. Photography made it possible to document
birds in the field with great accuracy. High-power spotting scopes today
allow observers to detect minute morphological differences that were
earlier possible only by examination of the specimen "in the hand".
A bird caught in a mist net
The capture and marking of birds enable detailed
studies of life history. Techniques for capturing birds are varied and
include the use of bird liming for perching birds, mist nets for
woodland birds, cannon netting for open-area flocking birds, the bal-chatritrap
for raptors, decoys and funnel traps for water birds.
A researcher measures a wild woodpecker.The bird's
right leg has a metal identification tag.
The bird in the hand may be examined and measurements can be made,
including standard lengths and weights. Feather moult and skull
ossification provide indications of age and health. Sex can be
determined by examination of anatomy in some sexually nondimorphic
species. Blood samples may be drawn to determine hormonal conditions in
studies of physiology, identify DNA markers for studying genetics and
kinship in studies of breeding biology and phylogeography. Blood may
also be used to identify pathogens and arthropod-borne viruses.
Ectoparasites may be collected for studies of coevolution and zoonoses.
In many cryptic species, measurements (such as the relative lengths of
wing feathers in warblers) are vital in establishing identity.
A California condor marked with wing tags
Captured birds are often marked for future
recognition. Rings or bands provide long-lasting identification, but
require capture for the information on them to be read.
Field-identifiable marks such as coloured bands, wing tags, or dyes
enable short-term studies where individual identification is required.
Mark and recapture techniques make demographic studies possible. Ringing
has traditionally been used in the study of migration. In recent times,
satellite transmitters provide the ability to track migrating birds in
near-real time.
Techniques for estimating population density include
point counts, transects, and territory mapping. Observations are made in
the field using carefully designed protocols and the data may be
analysed to estimate bird diversity, relative abundance, or absolute
population densities.
These methods may be used repeatedly over large
timespans to monitor changes in the environment. Camera traps have been
found to be a useful tool for the detection and documentation of elusive
species, nest predators and in the quantitative analysis of frugivory,
seed dispersal and behaviour.
In the laboratory
Many aspects of bird biology are difficult to study
in the field. These include the study of behavioural and physiological
changes that require a long duration of access to the bird.
Nondestructive samples of blood or feathers taken during field studies
may be studied in the laboratory. For instance, the variation in the
ratios of stable hydrogen isotopes across latitudes makes establishing
the origins of migrant birds possible using mass spectrometric analysis
of feather samples. These techniques can be used in combination with
other techniques such as ringing.
The first attenuated vaccine developed by Louis
Pasteur, for fowl cholera, was tested on poultry in 1878. Anti-malarials
were tested on birds which harbour avian-malarias. Poultry continues to
be used as a model for many studies in non-mammalian immunology.
Studies in bird behaviour include the use of tamed
and trained birds in captivity. Studies on bird intelligence and song
learninghave been largely laboratory-based. Field researchers may make
use of a wide range of techniques such as the use of dummy owls to
elicit mobbing behaviour, and dummy males or the use of call playback to
elicit territorial behaviour and thereby to establish the boundaries of
bird territories.
Studies of bird migration including aspects of
navigation, orientation, and physiology are often studied using captive
birds in special cages that record their activities. The Emlen funnel,
for instance, makes use of a cage with an inkpad at the centre and a
conical floor where the ink marks can be counted to identify the
direction in which the bird attempts to fly. The funnel can have a
transparent top and visible cues such as the direction of sunlight may
be controlled using mirrors or the positions of the stars simulated in a
planetarium.
The entire genome of the domestic fowl (Gallus gallus)
was sequenced in 2004, and was followed in 2008 by the genome of the
zebra finch (Taeniopygia guttata). Such whole-genome sequencing projects
allow for studies on evolutionary processes involved in speciation.
Associations between the expression of genes and behaviour may be
studied using candidate genes. Variations in the exploratory behaviour
of great tits (Parus major) have been found to be linked with a gene
orthologous to the human gene DRD4 (Dopamine receptor D4) which is known
to be associated with novelty-seeking behaviour. The role of gene
expression in developmental differences and morphological variations
have been studied in Darwin's finches. The difference in the expression
of Bmp4 have been shown to be associated with changes in the growth and
shape of the beak.
An Emlen funnel is used to study the orientation
behaviour of migratory birds in a laboratory.
Experimenters sometimes
place the funnel inside a planetarium to study night migration.
The chicken has long been a model organism for
studying vertebrate developmental biology. As the embryo is readily
accessible, its development can be easily followed (unlike mice). This
also allows the use of electroporation for studying the effect of adding
or silencing a gene. Other tools for perturbing their genetic makeup are
chicken embryonic stem cells and viral vectors.
Collaborative studies
Summer distribution and abundance of Canada goose
using data from the North American Breeding Bird Surveys 1994–2003
With the widespread interest in birds, use of a large number of people
to work on collaborative ornithological projects that cover large
geographic scales has been possible. These citizen science projects
include nationwide projects such as the Christmas Bird Count, Backyard
Bird Count, the North American Breeding Bird Survey, the Canadian EPOQ
or regional projects such as the Asian Waterfowl Census and Spring Alive
in Europe. These projects help to identify distributions of birds, their
population densities and changes over time, arrival and departure dates
of migration, breeding seasonality, and even population genetics. The
results of many of these projects are published as bird atlases. Studies
of migration using bird ringing or colour marking often involve the
cooperation of people and organizations in different countries.
Applications
Wild birds impact many human activities, while
domesticated birds are important sources of eggs, meat, feathers, and
other products. Applied and economic ornithology aim to reduce the ill
effects of problem birds and enhance gains from beneficial species.
Red-billed queleas are a major agricultural pest in
parts of Africa.
The role of some species of birds as pests has been
well known, particularly in agriculture. Granivorous birds such as the
queleas in Africa are among the most numerous birds in the world, and
foraging flocks can cause devastation. Many insectivorous birds are also
noted as beneficial in agriculture. Many early studies on the benefits
or damages caused by birds in fields were made by analysis of stomach
contents and observation of feeding behaviour. Modern studies aimed to
manage birds in agriculture make use of a wide range of principles from
ecology. Intensive aquaculture has brought humans in conflict
with fish-eating birds such as cormorants.
Large flocks of pigeons and starlings in cities are
often considered as a nuisance, and techniques to reduce their
populations or their impacts are constantly innovated. Birds are also of
medical importance, and their role as carriers of human diseases such as
Japanese encephalitis, West Nile virus, and influenza H5N1 have been
widely recognised. Bird strikes and the damage they cause in aviation
are of particularly great importance, due to the fatal consequences and
the level of economic losses caused. The airline industry incurs
worldwide damages of an estimated US$1.2 billion each year.
Many species of birds have been driven to extinction
by human activities. Being conspicuous elements of the ecosystem, they
have been considered as indicators of ecological health. They have also
helped in gathering support for habitat conservation. Bird conservation
requires specialized knowledge in aspects of biology and ecology, and
may require the use of very location-specific approaches. Ornithologists
contribute to conservation biology by studying the ecology of birds in
the wild and identifying the key threats and ways of enhancing the
survival of species. Critically endangered species such as the
California condor have had to be captured and bred in captivity. Such ex
situ conservation measures may be followed by reintroduction of the
species into the wild.
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