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J. Ornithol. 144, 253-270 (2003)
© Deutsche Ornithologen-Gesellschaft/Blackwell Verlag, Berlin
ISSN 0021-8375
The Colour of Birds: Hans Duncker, Pioneer Bird Geneticist*
Tim R. Birkhead 1, Karl Schulze-Hagen 2 and GOtz Palfner 1
1Department of Animal & Plant Sciences, University of Sheffield, Sheffield S 10 2TN, UK; 2Bergerstr. 163,
D-41068 M6nchengladbach, Germany
Summary
Hans Duncker (1881-1961) is among the first avian geneticists, but remains poorly
known. He trained as a biologist, completing his PhD at the University of GOttingen in
1905 and then became a high-school teacher in Bremen where he remained for the rest of
his life. In 1921 he met Karl Reich (1885-1970) who was the first person to make record-
ings of bird song and was well-known for creating a strain of canaries that sang Nightingale
(Luscinia megarhynchos) songs. Duncker provided a novel Darwinian/Mendelian explan-
ation for how Reich's canaries acquired their songs. In the early 1920s, a time during which
the field of genetics was rapidly developing in the USA and Britain, but not Germany,
Duncker and Reich conducted large-scale breeding experiments to establish the pattern of
inheritance of variegation and other traits in canaries. In 1925 Duncker met Generalkonsul
Carl Cremer (1858-1938), who provided the financial backing for a massive and compre-
hensive study of inheritance of colour patterns in Budgerigars (Melopsittacus undulates).
At the same time Duncker also initiated a project to create a red canary by hybridising
canaries with the Red Siskin (Carduelis cucullata). Duncker recognized that bird-keepers
had much to offer professional scientists (and vice versa) and was keen to bridge the gap
between them and to this end in 1927 began his own journal "Vtigel ferner L~inder". His
research on the genetics of the canary and budgerigar resulted in the publication of a large
number of papers in ornithological journals and magazines and several books. Duncker
was a eugenicist, and when the National Socialists came to power in 1933 he supported
and promoted the notion of positive eugenics. He was later (in 1990) condemned for these
activities and for having been a Nazi, but we show that Duncker joined the Party only
reluctantly. After WWII Duncker restored and re-catalogued the bird collections at the
Ubersee-Museum in Bremen. We discuss the possible reasons why Duncker's research,
much of it very innovative, has been largely ignored internationally.
Keywords:
Hans Duncker, Karl Reich, Carl Cremer, ornithology, avian genetics, canary, budg-
erigar, red canary, budgerigar mating expectations.
Zusammenfassung
Die Farbe der VOgel: Hans Duncker, ein Pionier der Vogelgenetik
Heute ist weitgehend verge ssen, dass Hans Duncker (1881-1961) einer der ersten Geneti-
ker in der Omithologie war. Aufgewachsen in Ballenstedt am Harz studierte er in G6ttin-
* Dedicated to RolfSchlenker on the occasion of his 65 th birthday
U.S. Copyright Clearance Center Code Statement: 0021-8375/2003/14403-0253 $ 15.00/0
254 Journal fiir Ornithologie 144, 2003
gen Naturwissenschaften und promovierte bei Ernst Ehlers tiber ein morphologisches
Thema. Ornithologisch wurde er durch seine Ubersichtsarbeit ,,Uber den Wanderzug der
VOgel" (1905) bekannt, die den Petsche-Labarre-Preis erhielt. Nach der Promotion land er
eine Anstellung als Lehrer ftir Mathematik und naturwissenschaftliche F~icher in Bremen,
wo er bis kurz vor seinem Tod lebte.
1921 begann seine Zusammenarbeit mit dem Kanarienztichter Karl Reich (1885-1970),
der als erster Vogelgesang auf Platte aufgenommen und einen Kanarienstamm geztichtet
hatte, der perfekt Nachtigallen imitierte. Duncker bot eine darwinistische Erkl/irung ftir
dieses Phgnomen, indem er klarstellte, dass Reich nicht Kanarien mit Genen fiir Nachti-
gallengesang, sondern lediglich VOgel mit besserem LernvermOgen herausgeztichtet hatte
(Duncker 1922a). Zu Anfang der 1920er Jahre, als die experimentelle Genetik noch weit-
gehend Neuland war, begannen Duncker und Reich mit Kreuzungsversuchen in grogem
Stil, um die Erblichkeit von Gefiederfarben und -strukturen, wie z. B. der Haubenbildung,
zu erforschen. Ab 1925 kooperierte Duncker auch mit Carl Cremer (1858-1938 I, einem
wohlhabenden Bremer Kaufmann. Cremer ermOglichte die Finanzierung und stellte seine
Volierenanlagen ftir die Untersuchungen der Vererbung von Farbmustern bei Kanarien
und insbesondere Wellensittichen zur Verftigung. Durch die Kreuzung mit dem Kapuzen-
zeisig
(Carduelis cucullatus)
wollte Duncker einen roten Kanarienstamm erzeugen. Dies
war deshalb so schwierig, da erst nach mehreren Generationen komplizierter Kreuzungs-
kombinationen fertile Nachkommen mOglich sind. Letztlich gelang es, das Gen fiir rote
Farbe vom Kapuzenzeisig auf Kanarien zu tibertragen. Dies ist das erste transgene Experi-
ment in der Ornithologie. Wirklich rote KanarienvOgel wurden jedoch erst Anfang der
1950er Jahre in England erzeugt (Gill 1955).
Mit seinen grogangelegten Kreuzungsexperimenten hat Duncker die Praxis der Vogel-
haltung und die theoretische Naturwissenschaft erfolgreich miteinander verkntipft. Er hatte
begriffen, dass Vogelhalter und Wissenschaftler gleichermagen voneinander profitieren
kOnnen. Ab 1927 gab er eine eigene Zeitschrift, ,VOgel ferner L~inder" heraus, die rasch zur
Verbandszeitschrift der AZ (Austauschzentrale der Exotenliebhaber und -ztichter) wurde.
Der enorm produktive Duncker publizierte ca. 75 Arbeiten, die Mehrzahl tiber Kreuzungs-
experimente und Vererbungsregeln bei Wellensittichen und Kanarien. Seine Vererbungs-
tabellen ftir Wellensittiche sind heute noch in Gebrauch (Elliott & Brooks 1999).
Als engagierter Eugeniker beftirwortete Duncker die Zwangssterilisation yon Behinderten
(Meyer & Duncker 1933), was ihm sp~iter vorgeworfen wurde (Walter 1990). Unterlagen
und Entnazifizierungsprotokolle im Bremer Staatsarchiv zeigen jedoch, dass Duncker
wegen fehlender Loyalitfit mehrfach in Schwierigkeiten geriet und erst 1940 unter Druck
Parteimitglied wurde.
Nach dem 2. Weltkrieg reorganisierte Duncker die Vogelsammlung des Bremer Obersee-
museums. MOgliche Griinde ftir die fehlende internationale Anerkennung Dunckers sind
in einer Fehlinterpretation seiner Experimente (Crew & Lamy 1934, 1935) und in der nach
dem 1. Weltkrieg einsetzenden Isolation der deutschen Wissenschaft zu suchen.
I. Introduction: Birth to 1918
Hans Julius Duncker was born in Ballenstedt
in the eastern foothills of the Harz Mountains
on 26 May 1881, the second of three sons. His
father Dr. Ernst Eduard Heinrich Duncker
(born 7 September 1848) was a high ranking
judge and businessman, whom Hans later
described as a dynamic and out-going person.
His mother was Marigrita (Marie Elisabeth)
Tim R. Birkhead et al. • Hans Duncker, Pioneer Bird Geneticist 255
Duncker, (formerly Uhde, born 24 August
1847 in Valparaiso, South America). It was his
grandfather who roused Duncker's interest in
natural history and birds in particular, for this
was a period when bird-keeping was especially
popular in Germany and elsewhere in Europe
(Haffer 2001). The family lived in Dessau,
which is where Duncker went to school, atten-
ding the Herzogliches Friedrichs-Gymnasium
(Ducal Friedrich's Secondary School) until
1900. Hans did well at school, especially in
maths, physics, sports and singing, but he
found French and English language less easy.
In the autumn of 1900 at the age of nineteen
Duncker went to the university at Grttingen to
study Mathematics and Natural Sciences, in-
cluding botany and physics. Between Easter
1901 and 1902 he made a year-long visit to the
University of Leipzig during which he decided
that zoology would be his main subject. On re-
turning to GOttingen he found a mentor in the
grandsigneur of morphology, Ernst Ehlers
(1835-1925), a close friend of Ernst Haeckel,
Germany's greatest popularizer - some would
now say vulgarizer - of Darwin's ideas (Stein
1988). One of Haeckel's several claims to
fame was plotting the branching paths of com-
mon descent-evolutionary trees, and although
Ehlers was much less obsessed with Darwin's
ideas, he was nonetheless influenced by Hae-
ckel (Nyhart 1995), and his comparative mor-
phology had its roots in evolution. In the early
1900s comparative morphology was one of the
main areas of zoological research, and Dun-
cker's PhD project which Ehlers supervised in-
volved comparing the internal structure of two
genera of marine worms. It was undoubtedly
through Ehlers and indirectly through Haeckel
whose popular works on evolution were best-
sellers in Germany during the first decade of
the twentieth century (Gould 1977, Stein
1988), that Duncker became a firm Darwinian.
Duncker was a model student and an active
member of two student bodies in Grttingen,
"Germania', the National Christian student
fraternity, and 'Schwartzburgbund" another
Christian society which approved of chastity
and disapproved of duelling, then popular
among Grttingen's male students. Interesting-
ly, any Christian beliefs that Duncker may ha-
ve held were not incompatible with his evolu-
tionary views.
Before completing his PhD thesis Duncker
was persuaded in 1904 by a student friend,
Friedrich Voss, to give a talk in the university
on bird migration. This was probably Dun-
cker's first public performance, and it was im-
mediately clear that he had a natural talent for
lecturing; the talk was an enormous success.
Duncker went on to make a more detailed stu-
dy of Eurasian bird migration routes, and in
1905 published a paper, 'Uber den Wanderzug
der Vrgel" on the topic. On 15 February 1905
he had the oral examination for his PhD thesis
which was entitled "Uber die Homologie von
Cirrus und Elytron bei den Aphroditiden. Ein
Beitrag zur Morphologie der Aphroditiden"
(About the homology of Cirrus and elytron
among the Aphroditids. A contribution to the
morphology of the Aphroditids: Duncker
1905a) and graduated with 'magna cum laude'
(second best grade) in Zoology, Botany and
Mathematics. One month later in November
1905 ~The Migration Paths of Birds', which
Duncker dedicated to 'his greatly admired tea-
cher Ernst Ehlers on the occasion of his 70 th
birthday', was awarded a prize by the Labarre
foundation (Faculty for Philosophy at Grttin-
gen University) and published by Gustav Fi-
scher, Jena as a book (Duncker 1905b). Dun-
cker then spent a year training as a high-school
teacher (of zoology, botany, mathematics and
physics), graduating in May 1906, when he
moved to Bremen to take a position as an auxil-
Iary science teacher at The Old Gymnasium, a
classical state school. He had hardly started as
as teacher when he had to undertake one year
of military service. Within a week of comple-
ting his military obligations, he married Elsa
Zwerusmann (born 4 June 1884 in Dessau) on
5 October 1907 in Dessau. Duncker now swit-
ched schools, moving briefly to the Realschule
am Doventor. In August 1908 Hans and Elsa's
first child Marigrita, was born - named after
256 Journal fur Ornithologie 144, 2003
relationships (Duncker 1912). In 1914 Duncker
published a series of school biology text books
for teachers, co-authored with a theologian
Friedrich Baade (Baade & Duncker 1914). On
24 April 1913 Hans and Elsa had a son, Hans-
Eberhard, but he died less than a year later on
27 January 1914. In 1915 the Dunckers moved
to Wernigeroderstr. 22, where they remained
until 1932. Their second daughter Lotti Hilde-
gard was born on 28 August 1915.
During World War I Duncker served as an
officer, first at the eastern front in Hungary,
Galicia, and Russia and then between 1915-
1918 at the western front in France. He was
awarded several medals and badges, including
iron crosses II and I, and was wounded once.
II. Duncker and Karl Reich
Fig.1. Hans Duncker aged 32 in 1913 (photo-
graph courtesy of Rolf Gramatzki).
Abb. 1. Hans Duncker im Alter von 32 Jahren im
Jahr 1913.
Duncker's mother. In 1909 Duncker changed
schools again, moving to the Realgymnasium,
an imposing boy's school on Hermann-B6se-
Strasse where he remained until the end of his
teaching career 1. Between 1907-1911 the
Dunckers lived at Moselstr. 38; and from
1911-1914 at Rheinstr. 6. In 1912, at the age
of 31 (Fig. 1), Duncker joined the German Or-
nithological Society. He conducted a study of
the biogeography of buntings in which he as-
sessed whether current and historic geographic
distributions could reflect their phylogenetic
Duncker met Ernst Karl Reich (1885-1970),
famous for his sound recordings of birds and
especially for his nightingale-canaries in Au-
gust 1921 when Duncker was 40 and Reich 36
(Fig. 2). Reich, who ran a family hardware
business on Fedelh6renstrasse in Bremen and
lived at Am Wall, had been fascinated by birds
and had bred roller canaries ever since he was
a boy. In 1911 he had bred one particular male
with an outstanding voice with a deep, rich
song similar to that of that of a Nightingale
(Luscinia megarhynchos).
It was this bird,
which Reich named Bar (Bear) that changed
his life and inspired him to breed a strain of
roller canaries that sang the nightingale's song.
In 1912 Reich performed a back-cross, mating
Bar to his mother and then provided their
offspring with a singing nightingale 'tutor'. It
was (and still is) standard procedure to provide
young roller canaries with a song tutor during
the sensitive song-learning phase (Speicher
1976), but normally the tutor was another ca-
nary. In fact, Reich had screened twenty diffe-
This school was known as the ~Realgynasium' from 1905-1937, but from 1937-1938 was the 'Oberschule
f'tir Jungen an der Kaiser Friedrich-Strasse' and from 1938-1945 as the 'Lettow-Vorbeck Schule', and sin-
ce 1957 as 'Gymnasium at the Hermann-Brse-Strasse'.
Tim R. Birkhead et al. • Hans Duncker, Pioneer Bird Geneticist 257
rent song birds as possible tutors for his young
canaries in the previous years (Von Der Grenze
1938), and had decided, as had many previous
bird-song enthusiasts before him, that the
nightingale had the best song. One of the pro-
blems Reich encountered in using the night-
ingale as a tutor for his young canaries was that
they had only a short singing season, and cea-
sed singing before the young canaries had fully
learned the song. He solved this by adjusting
the timing of the nightingale's moult and hence
its endogenous rhythm, following a method
described much earlier (Anon. 1772). Reich al-
so used his own recordings of nightingales to
train his canaries, although he preferred using
real birds (Von Der Grenze 1938).
By the time Reich and Duncker met, Reich's
nightingale-canaries were well established and
within canary circles at least well known, since
song canaries were still very popular at this
time (Gasser 2001). Reich believed that his
canaries had inherited their ability to sing a
nightingale song because, as he told Duncker,
after a few generations he no longer had to use
a nightingale tutor, and the quality of the birds'
song continued to improve with each successi-
ve cohort. The tutors of the young canaries now
were adult male nightingale-canaries singing
nightingale song. Reich believed that his cana-
ries had acquired the ability to sing the night-
ingale song by a Lamarckian form of
inheritance: the inheritance of an acquired
characteristic. It was this that piqued Hans
Duncker's imagination. Duncker was a firm be-
liever in Darwin's natural selection, and
suspected that Reich's Lamarckian interpretati-
on was probably wrong (Duncker 1922a).
Duncker was unusual for most ornithologists at
this period were Lamarckians and ideas based
on natural selection were often dismissed out of
hand (see for e.g. Allen 1893a, b, Keeler 1893).
The period between 1910 and 1930 was one
during which the study of genetics blossomed
(Provine 1971). Following the rediscovery of
Mendel's work in 1900 there had been a bitter
and largely futile debate between the Mendel-
ians, led by the British scientist William Bate-
Fig. 2. Hans Duncker (left) and Karl Reich in the
late 1920s (from Von der Grenze 1938).
Abb. 2. Hans Duncker (links) und Karl Reich in
den sp~iten 1920ern.
son, who believed that selection operated on
discontinuous traits, and the biometricians (led
by the British statistician Karl Pearson), who
believed that natural selection operated on the
almost imperceptile differences between indi-
viduals (see Provine 1971). By 1915 it was
clear to both sides that selection operated in
exactly the same way on both continuous and
discontinuous traits. Meanwhile in the USA
Thomas Hunt Morgan had focussed on the me-
chanisms of heredity, using
Drosophila
as his
study organism. Morgan had started by trying
to create mutations in various ways, including
X-rays, but it was a white-eyed fly in his regu-
lar stock (of red-eyed flies), that launched the
study of inheritance in 1910. Subsequently
Morgan and his co-workers discovered and
established the mode of inheritance of a large
number of mutations among their flies (Mor-
gan et al. 1915).
Duncker's explanation for how Reich's
nightingale-canaries acquired their song was
extremely novel. He concluded that Reich had
258 Journal fiir Ornithologie 144. 2003
not selected for those birds with the genes for
nightingale song, as Reich supposed, but in-
stead had unwittingly selected for those birds
that could learn the nightingale song from their
nightingale-canary tutors. A subtle, but import-
ant difference, and one that was entirely consi-
stent with a Darwinian view of evolution. Dun-
cker was justifiably pleased with his igenious
(and almost certainly correct) explanation, and
he wrote a succession of papers in a range of
different magazines and scientific journals de-
scribing Reich's birds (Duncker 1922a-e; see
also Von Der Grenze 1938). Unfortunately,
Duncker's clever idea seems to have been com-
pletely overlooked by subsequent researchers:
we have never seen Duncker's papers on
Reich's canaries referred to and Peter Marler,
one of the foremost bird-song specialists, ad-
mitted (pers. comm.) to not being aware of
Duncker's papers on this topic. Similarly,
Reich's pioneering experiment of training
birds to sing simply by playing them sound re-
cordings was virtually ignored. Twenty years
later when the study of song-learning in birds
was becoming a major part of the rapidly deve-
loping field of animal behaviour, there is a sin-
gle, tangential and somewhat deprecating com-
ment about Reich's work in "The Modem
Synthesis" (Huxley 1942). In a footnote on
p305 Huxley says that Ernst Mayr had told him
about a study in which canaries had been
taught to sing using recordings of nightingale
song 'carried out by a fancier named Reich,
but complete proof was not supplied'.
Once Duncker had become interested in
Reich's canaries he began to ask other ques-
tions relating to their genetics, including the
mode of inheritance of traits like plumage col-
our and crest. In 1923, using Reich's facilities,
they performed a large number of experimen-
tal pairings to establish the basis for the inheri-
tance of colour. They found that two yellow
birds invariably produced yellow offspring,
two green birds produced green offspring, but
crossing a yellow and a green bird or two va-
riegated birds produced variegated offspring.
In other words green plumage (the colour of
the wild canary) is dominant over yellow (the
domesticated form), but not in a straightfor-
ward way and Duncker concluded that at least
three genes were involved in the controlling of
the canary's colour. Two previous researchers
had looked at the inheritance of colour in can-
aries. In 1908 Florence Durham (sister-in-law
and research assistant to William Bateson)
established the basis for the inheritance of the
cinnamon mutation, which turned out to be sex
linked (Durham & Marryat 1908). In the USA
Charles Davenport (1908) had looked at the in-
heritance of variegation, and being a firm
Mendelian believed the transition from green
to yellow had occurred over just a few genera-
tions through the selection of sports. Daven-
port's study was riddled with errors and was
heavily criticised (Galloway 1909, 1910,
Heron 1910, Duncker 1928c).
The wild canary is predominantly green and
grey in colour with a yellowish head, breast
and romp. The familiar yellow domesticated
canary was produced during the 17th century
following approximately one hundred years of
selective breeding to eliminate all traces of
melanin (Birkhead, Schulze-Hagen and Kin-
zelbach, in press.; for a history of the canary
see Parsons 1987). It was, as Duncker showed,
precisely because colour in the canary is a
polygenic trait that it had taken so long to pro-
duce a yellow canary by artificial selection.
Duncker published the results of these canary
experiments in a number of different places,
including bird-keeping magazines, like "Die
Gefiederte Welt'" (Duncker 1924c), but also in
the scientific literature, including ~'Joumal fiir
Omithologie" (Duncker 1924e) because he
was keen to bridge the gap between the ama-
teur bird-breeder and the scientist and make
his scientific discoveries available to bird bree-
ders. As we will see, to a large extent Duncker
was successful, in part because bird-keeping
continued to be a respectable hobby in Ger-
many long after it ceased to be respectable in
Britain, and German scientists and ornitholo-
gists in particular were much more sympathe-
tic to bird-keeping than were ornithologists in
Tim R. Birkhead et al. • Hans Duncker, Pioneer Bird Geneticist 259
Britain, and indeed continue to be so (Anon.
1978, 1987, L6hrl 1989, Samstag 1988).
III. Duncker and Carl Cremer
Duncker was introduced to Generalkonsul Carl
Hubert Cremer (1858-1938) in the autumn of
1925 by Reich. Cremer (Fig. 3) was a wealthy
businessman, specialising in foreign trade
(Anon. 1928, Duncker 1927e, 1938b, Gebhardt
1964, Ringleben 1955). He was a member of
the Natural History Society of Bremen which
ran the museum, but this society also suppor-
ted bird-keeping. Cremer was president of the
AZ (Austausch-Zentrale der Exotenliebhaber
und Ztichter), the German Society of bird
keepers founded in August 1920 (and which
ran until about 1935). At his two Bremen
homes, one in the city at Am Dobben and the
other much larger property, Rosenau Villa at
Vahr about three km from the centre of
Bremen (and now built over) Cremer had a
large number of aviaries. His main interest was
in foreign birds and especially the different
colour forms of the Budgerigar
(Melopsittacus
undulatus).
Budgerigars had been first introduced into
Europe from Australia in 1840. The wild birds
are green in colour and the first colour muta-
tions appeared in captive stock; yellow in
1870 and blue in 1878 and others later (Vins
1993). But it was not until the 1920s that inter-
est in budgerigar breeding in Europe really
burgeoned, and Cremer was among the fore-
most enthusiasts. Being wealthy meant that he
could buy any new mutations that appeared in
other breeders' stock. It also meant that with
extensive breeding facilities he was in a good
position to establish these new mutations.
Cremer was a larger than life character; he
was a tall, imposing man with a great sense of
humour and was a self-confessed womaniser.
Despite Duncker's quieter, more conservative
nature, they got on very well and within a
short time had agreed to collaborate. Duncker
persuaded Cremer that between them (and this
included Reich) they could work out the gene-
Fig. 3. General Consul Carl Hubert Cremer in the
late 1920s/1930s (from Keidel 1960).
Abb. 3. Genralkonsul Carl Hubert Cremer in den
sp~iten 1920/1930er Jahren.
tic basis for all the budgerigar and canary mu-
tations. There was also another project that
Duncker wanted to undertake: to produce a
red canary. Having Cremer's generous finan-
cial backing was equivalent to Duncker secu-
ring a substantial grant from a research coun-
cil today - except that Duncker's studies of
avian genetics were conducted entirely in his
spare time while he was a school teacher.
Their collaboration provided unique opportu-
nities for Duncker and over the next few years
projected him into the position of leading
avian geneticist. However, while Duncker's
name is still well-known among the budgeri-
gar fancy (Vins 1993, Elliott & Brooks 1999),
he remains almost unknown among ornitholo-
gists and avian geneticists.
Duncker's idea of breeding a red canary was
a bold one. This idea may not have originated
260 Journal ftir Ornithologie 144, 2003
with him, but it was his knowledge of avian ge-
netics that made the red canary a possibility.
Duncker's ambition was to create what we
would now call a transgenic or genetically en-
gineered canary, taking the genes for red plu-
mage from the Red Siskin
(Carduelis cuculla-
ta) (also known as the Hooded Siskin), and
'placing' them in a canary. The Red Siskin, na-
tive to Venezuela, became known to science on-
ly in 1820 (Swainson 1820), and did not be-
come a cage-bird in Europe until the early
1900s (Coats 1985, Collar et al. 1992). Before
this however, it seems likely that the Spanish,
who were enthusiastic bird-keepers, had kept
them and transported them back to both the Ca-
nary Islands and Spain, where some of them hy-
bridised with canaries (Coats 1985, Collar et al.
1992). Breeding interspecific hybrids between
finches (usually European finches, such as the
Goldfinch
(Carduelis carduelis)
and canaries
had been popular ever since canaries were rou-
tinely bred in captivity (Stresemann 1923, Her-
vieux 1709), so it was not that surprising that
the Spanish hybridised Red Siskins and cana-
ries. These hybrids had attractive plumage and
voice. Starting in the 1890s Red Siskins were
imported into Europe in increasing numbers
(Astley 1902 a, b). Today, the Red Siskin is ex-
tremely threatened in the wild as a direct result
of this trade (Collar et al. 1992).
One of the first people in Britain to hybridise
Red Siskin and canaries was Horence Durham
sometime between 1908 and 1915 (Durham
1926). In Germany a fancier named Engels of
Tilsit, East Prussia also bred some Red Siskin
x Canary hybrids in 1912. He gave one of
these, a male, to A. Dams of K6nigsberg who
managed to back cross it to a female canary,
and although several young were produced
they all died. Dams then gave the original hy-
brid, which was obviously fertile, to Bruno
Matern of Rastenburg in central East-Prussia.
Matern was extraordinarily successful and
over several breeding seasons succeeded in
crossing this single hybrid with canaries to
produce a dynasty of orange coloured birds
(Dams 1926).
Duncker learnt of Matern's success and de-
cided to try to breed a red canary himself. His
original plan was to back-cross Red Siskin hy-
brids to ordinary yellow canaries, and select
only the reddest offspring for continued back-
crossing. Disappointingly for Duncker, he was
unable to produce anything other than coppery
coloured hybrids. Duncker's aim was to breed
a genetically red canary, not one that relied on
colour-feeding, which is what British fanciers
had done previously and subsequently did rou-
tinely .(Gill 1955). This was a frustrating pro-
ject because the genes from the two parent spe-
cies did not behave in the way Duncker
expected. Initially, he crossed Red Siskins to
yellow canary hens, but the offspring were
merely orange. Assuming that the genes for
producing red plumage from the Red Siskin in-
terfered with those for producing yellow plum-
age in the canary, Duncker went back to the
beginning and created new hybrids using do-
minant white canaries. These also failed to
produce red offspring, and again Duncker as-
sumed this was because the gene for yellow
plumage (which is recessive in the dominant
white canary) interfered with the production of
red colouration (Fig. 4). Duncker then propo-
sed that another white canary mutation, the re-
cessive white (which apparently carried no ge-
nes for yellow plumage), would produce
offspring of the required colour (see Duncker
1927a, 1931e, f, g, 1932c). Duncker gave up
on the red canary project at this point and the
crucial experimental pairings were conducted
by a British canary breeder, A.K. Gill who
was the vice-president of the British White
Canary Club and one of only three people in
the world (Duncker was another) to own reces-
sive white canaries (Gill 1955). Gill was even-
tually instrumental in producing a red canary -
albeit by a circuitous route (Birkhead 2003).
Soon after they met Cremer and Duncker
founded the German Budgerigar Society in
1925. A year later the British budgerigar socie-
ty was formed and the two groups kept in close
contact. Duncker and Cremer's objective was
to establish what colours would be produced
Tim R. Birkhead et al.. Hans Duncker, Pioneer Bird Geneticist 261
A.
W~iB-weig-P~rung.
B. Welg-gelb-Paarung.
e~
C, WeiB rnlt Kapuzenzeislg.
Fig. 4. Duncker's genetic schemes for predicting
the outcome of particular pairings: (A) Two domi-
nant white Canaries (showing the lethal homozy-
gous); (B) a dominant white and a yellow Canary,
and (C) a dominant white Canary and Red Siskin
(Kapuzenzeisig). (From Duncker 1927a).
Abb.4. Duncker's Schema zur Vererbung: (A)
Zwei dominante weige Kanarienvrgel (mit letaler
Homozygotie): (B) ein dominat weiger und ein gel-
ber Kanafienvogel; (C) ein dominat weiger Kana-
rienvogel und ein Kapuzenzeisig (aus Duncker
1927a).
when two varieties of budgerigar were cros-
sed: so-called mating expectations. There were
twelve recognised varieties of budgerigars at
this time and hence a potentially large number
of different crosses to perform to establish the
full range of mating expectations. However,
Duncker was extraordinarily efficient and by
establishing the genetic constitution of a subset
of varieties he was able to predict the likely
outcome of all other crosses. Luckily, many of
the budgerigar colour mutations involved one
or only a few genes, and the budgerigar project
made rapid progress. Duncker published the
results under his name, but usually with an
acknowledgement that the work had been con-
ducted in Cremer's aviaries. For the average
budgerigar breeder what Duncker had done
was to create order out of chaos, and once
breeders knew what to expect from their diffe-
rent pairings the budgerigar fancy could start
to develop particular varieties to their (arbi-
trary) exhibition standards (Vins 1993). Dun-
cker's results were translated and transmitted
around the world. The British Budgerigar So-
ciety honoured Duncker and Cremer by awar-
ding them a special gold medal each in 1927;
they couldn't attend the presentation at the
Crystal Palace bird exhibition in London in
1928 because Duncker was ill with kidney
trouble (for which he underwent extensive sur-
gery), but they did attend the next National Ex-
hibition in London in 1929 (Anon. 1929).
The late 1920s was an extraordinarily pro-
ductive time for Duncker (see Appendix A for
a list of Duncker's publications). He published
relentlessly, in both the ornithological literatu-
re and in bird-keeping magazines. His papers
were mainly about the inheritance of colour or
other traits in birds, but he also made a detailed
study of the colour of feathers based on their
microscopic structure (Duncker 1927c, k),
nest-building in weaver birds (Duncker
1927h), brood parasitism as an adaptation
(Duncker 1930a) and the role of X-rays in
creating mutations (Duncker 1930f). The idea
of bringing together the professional and ama-
teur bird cultures went even further and in
1927 Duncker began his own journal "Vrgel
ferner Lander". This became the official jour-
nal of the AZ. Prior to 1927 the AZ journal had
been a thin and poorly produced magazine, but
Duncker took it over and revitalised it.
In 1928 Duncker published his book "Gene-
tik der Kanarienvrgel" (Canary Genetics) and
the following year "Kurzgefasste Vererbungs-
lehre fur Kleinvrgel-Ztichter" (Concise Gene-
tics for Breeders of Cage-birds) which he dedi-
262 Journal fiir Ornithologie 144, 2003
cated to Reich and Cremer (Duncker 1928c,
1929e). Invitations to speak about his work at
conferences around the world started to arrive
and in 1930, accompanied by Cremer (who we
suspect paid Duncker's way) he gave talks in
Vienna, Ttibingen and at the International Or-
nithological Congress in Amsterdam (see Dun-
cker 1931c). Duncker was also invited to the
6th International Congress of Genetics in Itha-
ca, New York in 1932, at which he would have
been able to meet T. H. Morgan who was presi-
dent, but for some reason he did not accept.
Attempts to officially recognise and reward
Duncker in Germany for his extraordinary suc-
cess failed. In November 1930 Duncker's di-
rector at school, Herr Jentsch, asked whether
Duncker might be given the title of professor,
but this was rejected: because it 'contradicted
paragraph 4 of article 109 of the constitution
of the Reich'. The next month Alfred Ktihn,
Professor of zoology at G6ttingen sent a petiti-
on to the Bremen Senate asking whether they
would consider creating a position for Duncker
as an independent researcher, but that too was
turned down: 'Unfortunately there could hard-
ly be a more difficult moment to create an in-
dependent research position for Dr Duncker or
even substatially reduce his teaching duties. I
certainly do not have to explain the general fi-
nancial pressure on the Reich...' (see A Note
on Sources).
Duncker's experimental bird breeding
studies declined during the early 1930s and
by 1935 had ceased altogether, apparently
through a lack of funding.
IV. Duneker 1933-1945
In 1990 Hubert Walter published a paper high-
lighting Duncker's membership of the Nazi
party and describing his leading role in the
Unit of Racial Hygiene which existed at the
Natural History Museum in Bremen between
1931 and 1945 (Walter 1990). Walter 2 con-
demned Duncker's involvement with both
these organisations and declared him a dis-
grace to biology for so enthusiastically promo-
ting eugenic ideas. Walter acknowledged
Duncker's ability as a scientist and as a lectu-
rer, but found hard to understand how someone
so critical as a scientist could have been so un-
critical in his support for racial hygiene.
'Duncker was' Walter wrote 'one of the very
many Germans who readily accepted and pro-
pagated the aims of the National Socialists'
racial politics and hence contributed to the fact
that these aims became a cruel and deadly rea-
lity for many human beings'. Walter was also
particularly critical of Duncker because unlike
many other Nazis, Duncker never renounced
his views after the war.
Since Walter's important paper was pub-
lished new information has come to light, and
a somewhat different view of Duncker's invol-
vement with both the Unit for Racial Hygiene
in Bremen and the Nazi party, now emerges.
This new information is the transcript of Dun-
cker's interview with the Allies following the
end of WWII: we refer to this as the Allies' In-
terview (see A Note on Sources).
Duncker was probably always a supporter
of eugenic ideas, possibly stemming from
Haeckel's popular and influential writings on
social Darwinism (Stein 1988). Eugenic ideas
were also widespread elsewhere in Europe and
in the United States throughout the first two de-
cades of the twentieth century (Allen 1978,
Gould 1977, Stein 1988). Duncker appears to
have been extremely highly principled inas-
much that if he believed something, he did so
in an uncompromising fashion, and it is to this
that we attribute his reluctance to retract his eu-
genic views after the end of WWII.
Duncker became vice-president of the Natu-
ral History Society in Bremen in 1931, and in
2 Walter never met Duncker and obtained the information for his paper from Duncker's own published and
unpublished manuscripts. Nor did Walter have access to the transcript of Duncker's interview with the Al-
lies or his personal record held at the Staatsarchiv in Bremen (H. Walter, pers. comm.).
Tim R. Birkhead et al. • Hans Duncker, Pioneer Bird Geneticist 263
1933 together with the president Hans Meyer
(director of the X-ray therapy service in Bre-
men), he started the sub-unit for racial hygiene.
The first society for racial hygiene in Germariy
had been established in 1905 and Duncker and
Meyer's sub-unit was one of many that sprang
up in Germany during the 1930s. At this time
almost every German university had a chair in
racial hygiene and offered undergraduate cour-
ses on it. Initially at least, most academic euge-
nicists were not overtly anti-Semitic, and fo-
cussed instead on the mentally retarded
(Deichmann 1996). After seizing power in
1933 the Nazis quickly introduced a law advo-
cating the sterilisation of the mentally retarded
for the 'common good before the individual'.
In response to this announcement Duncker and
Meyer organised a series of five public lectures
under the umbrella title "The Prevention of Un-
worthy Life", which were given during March
and April 1933 by a biologist, a sociologist, a
psychiatrist, a theologian and a professor of
law (Meyer & Duncker 1933). The sterilisation
law wasn't due to come into effect until early
1934 and these lectures were apparently de-
signed to allow people time to discuss the idea.
Given the title of this series of lectures, it is
hardly surprising that Walter was sharply criti-
cal of Duncker. However, reading them now,
they are not as extreme in advocating eugenic
ideology as one might imagine. Nonetheless,
from 1933 and throughout much of the war
Duncker continued to lecture on and publicise
eugenic ideas.
On coming to power one of the things Hitler
did was to enoble biology as a school subject,
much to the delight of biology teachers in
schools and universities who had long felt that
biology had been under-rated in Germany
(B~iumer-Schleinkofer 1995). The new regime
provided Duncker with an opportunity to util-
ise his expertise as a teacher, and together with
Dr Friedrich Lange, a high school teacher from
Hamburg, he edited a volume which incorpo-
rated Nazi ideology into biology teaching
(Duncker & Lange 1934). Duncker was not
alone in taking advantage of the educational
opportunities provided by the new regime, and
this book was merely one among many that ap-
peared in the early 1930s (B/~umer 1990, B/iu-
mer-Schleinkofer 1995).
From the foregoing one might imagine that
Duncker would have joined the party imme-
diately the Nazis came to power in 1933, but
in fact he did not do so until 1940. Duncker
revealed in his Allies' Interview that he had
been 'encouraged" to join the Nazi party by
Senator Richard Hoff (president of the Unit of
Racial Hygiene in Bremen) by being offered
the prestigious position of director of the Kai-
ser-Wilhelm-Institute for Genetics in Berlin-
Dahlem early in 1933. He declined, partly be-
cause he did not want to join the Nazi party
and because he did not want to be seen as an
opportunist. Moreover, he felt that the position
should go to a botanist and professional biolo-
gist, rather than a teacher who did research as
a hobby (see A Note on Sources). It also
seems likely to us that Duncker recognised his
own limitations and that he might have strug-
gled in such a position 3. The Nazis continued
to 'encourage" Duncker by offering him the
post of inspector of biology books in 1934. He
accepted, but this position did not last long
however, for in 1934 he was denounced by
someone at his school for making insulting
remarks about Hitler. The ensuing investigati-
on found no evidence for this however and no
formal disciplinary measures were taken
against Duncker by the Nazis. Nonetheless,
the denouncement did have negative effects:
the Nazis actively discouraged him from
giving public lectures and his prospects of
promotion at school disappeared. The next
year Duncker's superiors at school tried once
more to persuade him to join the Nazi party,
and again he refused. The Nazis then began
a more negative form of persuasion, by ap-
3 The position went to Fritz von Wettstein, then considered to be the foremost plant geneticist in Germany,
who ironically never joined the Nazi party.
264 Journal fur Ornithologie 144, 2003
pointing additional editors, Party members
E. Schtitze and W. Schinke, to Duncker's jour-
nal "V6gel ferner L~inder", thereby diluting
Duncker's influence, although, as Duncker
said in his Allies' Interview, he continued to
do all the work. Duncker's contributions to
the journal fell sharply during this period.
In 1936 Duncker's application for promoti-
on to senior master at school was rejected by
the Nazi party, who in a letter dated 11 August,
said: 'We recommend the temporary postpone-
ment of the intended promotion of master
"Studienrat" Dr. Hans Julius Duncker, Bremen
for one year. His attitude towards national so-
cialism does not convince us that he is inter-
nally totally dedicated to our movement. The-
refore we think that a blocking period is still
essential.'
Duncker was finally promoted to Oberstu-
dienrat (senior master) in 1939, but as he told
the Allies, this was only because by then the
Nazis no longer insisted on approving promo-
tions. Early in 1940 he was once again under
pressure to join the party and again he refused.
Finally, when the Nazis presented him with a
completed application form later that year,
Duncker capitulated and signed.
Duncker 4 told his Allies interviewers that he
had welcomed the racial hygiene laws in 1933
which focussed on the sterilisation of the men-
tally retarded and the encouragement of large,
healthy families, but that he had never perso-
nally discriminated against the Jews (but see
Walter 1990 referring to Duncker 1933a).
MoreOver, as the war continued, he became in-
creasingly disillusioned by the Nazis' beha-
viour. On completing their interview the Allies
classified Duncker as a "Mitl~iufer" - hanger
on. However, in itself this is not very informa-
tive since "Mitl~iufer" was one of the common-
est classifications made by those involved in
the largely ineffectual denazification process
(Napoli 1949).
V. Post-war and Retirement 1945-1961
After the Allies' invasion and the end of WWII
Duncker, along with many other Nazi school-
teachers, was suspended from his teaching po-
sition. This was both a blow to his pride and a
serious threat to his livelihood since at start of
the war Duncker had been vicarious deputy di-
rector and was regarded as both a skilled and
popular teacher (M. Birkmann, pers. comm.5).
Not until 1948, when Duncker was 67, was he
allowed to retire and officially receive a pensi-
on. He and his wife Elsa continued to live at
Mathildenstrasse 78, where they had moved in
1932, but in 1954 they moved further up the
street to Mathildenstrasse 37 where they remai-
ned. He was appointed honorary curator at the
Natural History Museum in Bremen and set ab-
out restoring the bird collections which had be-
en damaged and neglected during the war. The
bird collection in Bremen was of special signi-
ficance since much of the material had been
collected by the previous curator Gustav Hart-
laub (1814-1900). During the late 1940s and
early 1950s Duncker restored and re-catal-
ogued the entire collection of 16,000 bird skins
(Duncker 1953) for which the museum director,
H. Wagner was very grateful (Wagner 1957).
Duncker continued to give public lectures at the
fQbersee-Museum, on topics including birds, in-
heritance and chromosomes, and judging from
contemporary newspaper cuttings, he had retai-
ned his ability to inspire an audience.
Although Duncker had long since given up
any bird breeding research he continued to be
consulted by the editor of "Die Gefiederte
Welt", Joachim Steinbacher on avicultural
matters, such as nomenclature for the increa-
sing number of colour canary mutations. In
4 It is difficult to know how honest anyone might be during such an interview, but everything we have been
able to check coincides with Duncker's statements, which in turn is consisent with our view that he was
highly principled and honest.
5 M. Birkmann was a former pupil of Duncker's at the Lettow-Vorbeck School.
Tim R. Birkhead et al.. Hans Duncker, Pioneer Bird Geneticist 265
1951 on the occasion of his 70th birthday the
Bremen Natural History Society celebrated
Duncker's achievements by making him an
honorary member. Throughout his 70s Dun-
cker continued to visit the museum almost eve-
ry day. In 1960 Duncker's wife died, and a
year later in September 1961 he was taken
seriously ill. Unable to care for himself he was
taken to live with one of his daughters at Saar-
brticken, where he died on 22 December 1961.
VI. Overview
Duncker's main achievement was establishing
the genetic basis for colour and other mutati-
ons of canaries and budgerigars. Some of these
were straightforward and involved single auto-
somal gene effects, others were more compli-
cated, involving sex-linkage and polygenic
traits. In this respect Duncker's research follo-
wed very much in the mould of that of T. H.
Morgan: identifying the genetic basis of muta-
tions. That Duncker was a first rate scientist, is
best exemplified by his ingenious interpretati-
on of how Reich's canaries acquired their
nightingale song. Duncker (1922a) presented
his explanation as an hypothesis and a set of
clear, testable predictions, although it is not
clear whether he ever conducted the necessary
experiments (which would have needed sound-
proof cages).
It is clear that by 1930 Duncker's success
was recognised in Germany and his invitations
to international conferences shows that his
work was beginning to be recognised else-
where. There are probably two main reasons
why Duncker's scientific work was sub-
sequently ignored internationally. First, he did
not discover any general biological principles.
In terms of genetics he was a follower rather
than a leader, although within the field of avian
science he was genuinely innovative, as
illustrated by his ideas on the mechanisms of
heredity of budgerigar colours. However, these
particular ideas, referred to as the 'FOB theo-
ry' (see Watmough 1935 for details), were
later declared by an English geneticist, Francis
Crew to be incorrect (see Crew & Lamy 1934,
1935) and must have been a devastating blow
to Duncker. Crew & Lamy (1934) state: 'We
do not wish to minimise the work of these
scientists [Duncker and Dr Hans Steiner,
another budgerigar researcher, Professor of
Zoology in Ziirich, Switzerland; see Gebhardt
1970]; we merely point out that their theories
are not helpful to the breeder. Their analysis of
the physico-chemical differences which exist
between the various mutant forms of the
budgerigar as compared to the wild type light
green is a most important work; but it is not ge-
netical analysis, and it is not necessary to the
practical application of genetical principles.
Moreover, when they assign definite develop-
mental processes arbitrarily to this or that fac-
tor, it must be said that they go beyond the con-
clusions warranted by the facts, and ignore
much of the results of experimental genetics of
the past twenty years'. In fact, Crew's harsh
criticism was'based on Duncker's assumption
that the biochemical pathways controlling co-
lour was determited by a single gene rather
than several genes.
The second main factor contributing to
Duncker's lack of international scientific re-
cognition may have been the isolation of Ger-
man researchers immediately following WWI,
and especially after WWII for those working
in genetics or eugenics (Deichmann 1996).
Duncker's Nazi-links, which were well known
to those who worked with him immediately af-
ter the war (G. von Wahlert, pers. comm.) and
later publicised by Walter (1990), may have
contributed to his lack of subsequent recogniti-
on. In this respect it may be significant that
Duncker never received a proper obituary 6 in
6 The AZ journal did publish a 'death notice' of Duncker (Keidel 1962), but as far as we are aware the AZ
never published any other account of Duncker's scientific contribution or his revitalisation of the AZ in
1927 when he launched "Vogel ferner L~inder".
266 Journal ftir Ornithologie 144, 2003
the AZ journal (reinstated after WWlI as the
AZ Jahrbuch) even though they published a
number of articles on the history of the society
containing individual photographs of several
of the key figures, such as Cremer, but curious-
ly, not Duncker (Keidel 1960, 1962). Other
contributory factors probably include the fact
that Duncker's papers were all published in
German, and that ~real" ornithologists studied
wild rather than domesticated birds. Finally, it
seems likely that many scientists failed to see
the relevance of Duncker's research for wild
birds, although now, following the molecular
revolution, the study of avian genetics, sexual
selection and bird colouration is entering a
new and exciting phase (Hill 2002) and may
turn the spotlight back onto some of Duncker's
pioneering studies.
A Note on Sources
We have pieced together Duncker's private
and scientific life from obituaries (Anon.
1962a, b, Steinbacher 1962, Stresemann 1962,
Gebhardt 1964), other brief accounts (e.g. Kei-
del 1962, Wagner 1957, Ringleben 1955) and
from Walter (1990). In addition, we used the
typescript of the Allies' Interview and his ~per-
sonal record' held at the Staatsarchiv in Bre-
men. The attempts by both Jentsch and Alfred
Ktihn to promote Duncker is documented in
two letters dated 8 November 1930 and 2 Ja-
nuary 1931, respectively, held in the Bremen
Staatsarchiv. Senator Richard Hoff's offer to
Duncker of the directorship of the Kaiser-Wil-
helm-Institute in Berlin-Dahlem in 1933 which
he reported in the Allies' interview has not be-
en verified. However, the KWI's files for this
period are far from being complete, since
much was lost during and after the wax" (Ms.
Kazemi, Max-Planck archive in Berlin, pets.
comm). Another possibility is that the offer
was made only verbally. The fQbersee-Museum
in Bremen holds a small number of Duncker's
personal papers dating from the late 1940s and
1950s. We talked to a few people that knew or
knew of Duncker, including Klaus Speicher,
Joachim Steinbacher and Gerd von Wahlert.
Duncker published 'popular' accounts of ma-
ny of his findings in avicultural magazines or
newspapers, such as Kanaria which came out
weekly, (but is no longer published and copies
from the 1920s and 1930s are now very diffi-
cult to locate). Kanaria had no volume num-
bers so we refer to it by year and week number.
In some instances we had photocopies of
Duncker's articles but no page numbers -
hardly ideal, but we felt it was better to include
them as they are rather than not at all.
Acknowledgements
A great many people have helped us locate information
about Hans Duncker, Karl Reich and Generalkonsul Carl
Hubert Cremer. We are extremely grateful to all of them,
especially: Ishbel Avery, Peter Berthold, Linda Birch at the
Alexander Library in Oxford, Michael Birkmann, Martin
Bossert, Clive Catchpole, Hans Classen, Nigel Collar,
Elaine Dean in the inter-libn~ry loans department Sheffield
University Library, Eberhard Focke, Armin Geus, Rolf
Gramatzki, Ms. Kazemi from the Max-Planck archive in
Berlin, Christoph Knogge, Bernd Leisler, Peter Marler,
Monika Marschalck at the Staatsarchiv in Bremen whose
assistance in providing access to Duncker's personal files
and the transcript of his interview with the Allies was inva-
luable, Ernst Mayr, Rolf Nagels, Rosemarie Neif at the
Wiener Library in London, Tom Pizzari, and especially
Rolf Schlenker without whose help and_ encouragement
this study would not have been possible, H. Schwarzw~.l-
der, Joachim Seitz, whose help in Bremen is much appre-
ciated, Klans Speicher, Ray Steele who was especially
helpful with the budgerigar literature, Adrien Taylor at the
Boise University Library sent nmch useful information,
Geoff Walker, Gerd von Wahlert who worked with Hans
Duncker in the 1950s shared his memories with us, Hubert
Walter, David Whittaker and Kevin Wirick. We thank Jfir-
gen Haffer for helpful discussion and comments on the ma-
nuscript.
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Accepted: 18 February 2003
Appendix A.
A list of Duncker's publications
Baade, E, and H. Duncker. 1914. Der menschliche K6rper
nach Leben, Bau und Pflege. Herman Schroedel, Halle on
Saale. [The Human Body according to its Life. Structure
and Care]
Duncker, H. 1905a. Uber die Homologie yon Cirrus und
Elytron bei den Aphroditiden /Ein Beitrag zur Morpholo-
gie der Aphroditiden). Zeitschr. f. Wiss. Zool., 81, 191-
276. [On the morphology of Cirrus and Elytron in Aphrodi-
tes]
Duncker, H. I905b. Wanderzug der Vrgel. Jena:
Petsche-Labarre-Stiftung. [Migration Paths of Birds]
Duncker, H. 1912. Die Verbreitung der Gattung Emberi-
za, eine ornitho-geographische Studie. J. Ore. 60, 69 95.
[The distribution of the genus Emberiza an ornitho-geogra-
phical study]
Duncker, H. 1922a. Die Reich'sche Gesangeskreuzung
(Nachtigall u. Kanarienvogel) eine ,,erworbene" Eigen-
schaft. J. Orn, 70, 423-430. [The song hybrid of Reich
(nightingale/caImry); an 'acquired' character - preliminary
contribution]
Duncker, H. 1922b. Die ,Nachtigallen-Schl~iger" des
Hem Reich, Bremen. Gefiederte Welt, 51, 65-66. [The
"Nightingale Singers" of Mr. Reich, Bremen]
Duncker, H. 1922c. Die ,,Nachtigallen-Schl~ger" des
Hem Reich, Bremen. (part II). Gefiederte Welt, 51, 73-74.
Duncker, H. 1922d. Die ,,Nachtigallen-Schl~ger" des
Hem Reich, Bremen. Conclusion. Gefiederte Welt, 51, 81-
82.
Duncker, H. 1922e. Nachtigall-Kanarienh~hne. Kosmos,
5, 129-130.
Duncker, H. 1922f. Der Reichsche Stamm. Kanaria, 15,
00-00. [The Reich's Strain]
Duncker, H. 1923a. Aus der Geschichte der Kanarienvr-
gel. Die Kanarienvrgel, 11, 48-49. [Aspects of the History
of Canaries]
Duncker, H. 1923b. Die Erblichkeit der Scheitelhaube
bei Kanarienvrgeln. J. Orn., 71,421 447. [Genetics of the
crest in canaries]
Duncker, H. 1923c. Geschlechtsbestimmunng bei Tie-
ren, Der Kanarienvogel, 12, 13. [Sex determination in ani-
mals]
Duncker, H. 1924a. Ein eigenartiger Bastard von Stieg-
litz und Kanarienvogel. Der Kanarienvogel, 12, 6. [A pecu-
liar hybrid between a goldfinch and a canary]
Duncker, H. 1924b. Einige Beobachtungen tiber die Ver-
erbung der weissen Parbe bei Kanarienvrgeln. Zschr. f.
Ind. Abst. u. Ververbl. 32, 363-376. [Some observations
on the inheritance of the white colour in canaries]
Duncker, H. 1924c. Exakte Vererbungsversuche bei Ka-
narienv0geln (parts I-VIII). Die Gefiederte Welt, 53, 2 5,
11-13, 19-22, 26-28, 34-36, 43-45, 50-52, 58-60. [Ex-
act genetic experiments with canaries]
Duncker, H. 1924d. Vererbungsstudien an Kanarienvr-
geln. Wiss. Beil. d. Weser. Ztg., 12 June, [Genetic experi-
ments on canaries]
Duncker, H. 1924e. Vererbungsversuche an Kanarienvr-
geln, IIL Haubenfaktor. Weissfaktor. Scheckproblem. I.
Orn., 72, 314-381. [Genetic experiments on canaries III.
crest factor, white factor, variegation]
Tim R. Birkhead et al.. Hans Duncker, Pioneer Bird Geneticist 269
Duncker, H. 1924f. Wie entstehen unsere Haustierrras-
sen? Kanaria, 22, 000-000. [How do our domestic breeds
arise?]
Duncker, H. 1925. Reingelbe Isabellen. Kanaria, 19,
261-262. [Pure Yellow Isabels]
Duncker, H. 1927a. Bastarde yon Kapuzenzeisig und
weissem Kanarienvogel. VOgel ferner Lander, 1, 67-74.
[Hybrids of hooded siskin and white canary]
Duncker, H. 1927b. Erbformeln und Methode zur Be-
rechnung der Nachzucht eines Wellensittichpaares. VOgel
ferner Lander, 1,112. [Genetic formulas and method to cal-
culate the offspring of a pair of budgerigars]
Duucker, H. 1927c. Der Ausfall des Fettfarbstoffes in
den epidermoidalen Gebilden auf Grund erblicher Veranla-
gung (Alipochromismus) bei Kanarien und Wellensitti-
chen. Zschr. f. ind. Abst.- u. Vererbl. 45, 41-86 [Lack of
lipophyllic pigments in epidermal structures because of a
genetical disposition 'alipochromismus' in canaries and
budgies]
Duncker, H. 1927d. Der Geltungsbereich des Mendelis-
mus. Abh. Vortr. Bremer Wiss.fes Reihe D. Bd., 1, 251-
279. [The limits of Mendelism]
Duncker, H. 1927e, Die Vogelhanser yon Herrn General-
consul C.H. Cremer, Bremen. VOgel ferner Lander, 1,166-
174. [The aviaries of General Consul C.H. Cremer, Bre-
men]
Duncker, H. 1927f. Ein Bastard zwischen Stieglitz-
mannchen und Weibchen eines weissen Kanarienvogels.
VOgel ferner Lander, 1, 106 107. [A hybrid between gold-
finch cock and female white canary]
Duncker, H. 1927g. Erbformeln und Methode zur Be-
rechnung der Nachzucbt eines Wellensittichpaares. VOgel
ferner Lander, 1,112 [Genetic formulas and method to cal-
culate the offspring of a pair of budgerigars]
Duncker, H. 1927h. Ober die Webetatigkeit der Weber-
v6gel. VOgel ferner Lander, 1, 145-149. [About the wea-
ving activity of weaving birds]
Duncker, H. 1927i. Von auslandischen Zfichtern und
Liebhabern. VOgel ferner Lander, 1, 96-100. [About fo-
reign breeders and enthusiasts]
Duncker, H. 1927j. Von Ziichtem und von Vererben. VO-
gel ferner Lander, 1, 7-15. [Inheritance and the breeder]
Duncker, H. 1927k. Wie entsteht die Farbenpracht der
Vogelfeder? VOgel ferner Lander, 1,125-139. [What crea-
tes the beautiful colours of birds' feathers?]
Duncker, H. 1928a. Die Vererbung der Farben bei Wel-
lensittichen. VOgel feruer L~inder, 2, 9-34. [The genetics of
colour in budgerigars]
Duncker, H. 1928b. Faktorenkoppelung bei Wellensitti-
chert. VOgel feruer Lander, 2, 206-220. [The coupling of
factors in budgerigars]
Duncker, H. 1928c. Genetik der KanarienvOgeln. Bibl.
Genet., 4, 40-140. [Canary Genetics]
Duncker, H. 1928d. Glanzstare. VOgel femer Lander, 2,
140. [Glossy starlings]
Duncker, H. 1928e. Von auslandischen Ziichtern und
Liebhabern. VOgel ferner Lander, 2, 132-133, 188-191.
[About foreign breeders and enthusiasts]
Duncker, H. 1928f. Zusammenstellung der in den Vogel-
zuchtanlagen yon Herrn Generalkonsul C.H, Cremer, Bre-
men durchgeftihrten Vererbungsversuche. Abh. naturw.
Verein. Bremen 26:659-664. [Summary of the genetical
experiments on coloured budgerigars pertbrmed in the
aviaries of Generalkonsul Cremer, Bremen]
Duncker, H. 1928g. Das Wesen der Erbfaktoren. Abh.
naturw. Verein. Bremen 26:633-658. [The essence of here-
dity]
Duncker, H. 1929a. Das Problem der Graufltigelverer-
bung bei Wellensittichen. VOgel ferner Lander, 3,208-222.
[The problem of genetics of grey wings in budgerigars]
Duncker, H. 1929b. Farbenvererbung bei BuntvOgeln.
Vogel ferner Lander, 3, 90-109. [Colour genetics in colour
birds]
Duncker, H. 1929c. Genetik der KanarienvOgel. Der
Z~icbter, 1. [Canary Genetics[
Duncker, H. 1929d. Genetik der Wellenstittichen. Der
Z0chter, 2. [Budgerigar Genetics]
Duncker, H. 1929e, Kurzgefasste Vererbungslehre fiir
Kleinv6gel-Ztichter. Leipzig: Dr. E Poppe. [Concise Gene-
tics for Breeders of Cage-birds]
Duncker, H. 1929g. Wellensittichpaarungen mit eindeu-
tiger Nachkommenschaft. Vogel ferner L~inder, 3, 181-
182. [Budgerigar pairings with predictable offspring]
Duncker, H. 1930a. Der Brutparasitismus der Witwen
und das biologische Anpassungsproblem. VOgel feruer
Lander, 4, 146-152. [Brood parasitism of widows and the
biological problem of adaptation]
Duncker, H. 1930b. Fettfarbstoffvererbung bei Kana-
rienv6geln im Lichte der Goldschmidtschen physiologi-
schen Vererbungstheorie. Zschr. f. ind. Abst. Vererbl, 54,
267 271 [Inheritance of lipid pigments in canaries in the
context of Goldschmidt's physiological theory of inheritan-
ce]
Duncker, H. 1930c. Graufltigelpaarungen mit eindeuti-
ger Nachkommenschaft. VOgel ferner Lander, 4, 103-113.
[Grey wing pairings with unambiguous offspring]
Duncker, H. 1930d. Neue Ergebnisse von Wellensittich-
paarungen. VOgel ferner Lander, 4, 9-21. [New results
from budgerigar pairings]
Duncker, H. 1930e. Wieder Wellensitfich-Halbseiter.
V6gel femer Lander, 4, 232-234. [Budgerigar "'half sider"[
Duncker, H. 1930f. R6ntgenstrahlen und Keimschadi-
gung. Strahlentherapie. 37, 142-163. [X-rays and embryo
damage]
Duncker, H. 1931a. Das Scheckungsproblem bei Kana-
rienv6geln. Kanaria, 27, 342-343. [The Variegation Pro-
blem with Canaries]
270 Journal far Ornithologie 144, 2003.
Duncker, H. 1931b. Die Verbreitung der Brillenv6gel.
Vdgel ferner Lander 5, 146-154. [The distribution of the
spectacled birds]
Duncker, H. 1931c. Erblichkeitsverb~lmisse bei Vogeln.
in: VIith International Ornithological Congress, 1930 (Ed.
by Beaufort, L. E de), pp. 215 243. Amsterdam: Beaufort
L. f. de. [Genetics in birds]
Duncker, H. 1931d. Farbenbezeichnungen bei Kanarien-
v/Sgeln. Kanaria, 38, 477 478. [Colour Classes of Cana-
ries]
Duncker, H. 1931e. Farbenzucht bei Kanarienv6geln.
1. Kanaria, 5, 61-62. [Canary Colour Breeding. 1]
Duncker, H. 1931f. Farbenzucht bei Kanarienv/Sgeln.
2. Kanaria, 17, 221-223. [Canary Colour Breeding. 2]
Duncker, H. 1931g. Farbenzucht bei Kanarienv6geln.
3. Kanaria, 23,293-295. [Canary Colour Breeding. 3]
Duncker, H. 1931h. Neues yon der Faktorenkoppelung
bei Wellensittichen. Vdgel ferner L~nder, 5.91 96. [News
about factor coupling in budgerigars]
Duncker, H. 1932a. Neues zum Halbseiterproblem. Vd-
gel ferner Lander, 6, 17-23. [News about the "half sider"
problem]
Duncker, H. 1932b. Wie entstehen neue Farbenschlage,
und was kann der Ztichter zur Erzielung derselben tun? Vd-
gel ferner Lander, 6, 57-65. [How do new colour variations
emerge and what can the breeder do to obtain them?]
Duncker, H. 1932c. Wie z(ichtet man Farbwellensittiche
und Farbenkanarien? Gefiederte Welt, 61, 313-316. [How
to breed coloured budgerigars and canaries.]
Duncker, H. 1933a. Biologie des Volkskdrpers. Bremer
Beitr~ge zur Naturwissenschaft, 1, 93 112. [Biology of the
[German] people]
Duncker, H. 1933b. Isabellwellensittiche. Vdgel ferner
Lander, 83-85. [Isabelle budgerigars]
Duncker, H. 1933c. Was sind Mutationen? Kanaria, 1, 2.
[What are mutations?]
Duncker, H. 1933d. Wellensittiche in Freiheit. VOgel fer-
ner Lander, 7, 79-83. [Budgerigars in nature]
• Duncker, H. 1933/34. Die Vererbungslebre in der Ztich-
terpraxis. Pp. 53-73. Handbuch ftir die Mitglieder des
VDK 1933-34.
Duncker, H. 1934a. Die stofflichen Grundlagen der Ver-
erbung. Bremer Beitrfige zur Naturwissenschaft Bd, 2, 80-
109. [The material basis of genetics]
Duncker, H. 1934b. Neues yon der Wellensittchzucht in
England. Vdgel ferner Lander, 35-38. [News about budger-
igar breeding in England]
Duncker, H. 1938a. Farbenzucht. III. Die Karthothek-
karte. Kanarim 1, 4-5.[Colour breeding III. The Registar
Card]
Duncker, H. 1938b. Generalkonsul Carl Hubert Cremer.
Gefiederte Welt, 15, 169-171. [Gemeralkonsul Carl
Cremer]
Duncker, H. 1953. Mitteilungen aus der Bremer Vogel-
sammlung. Abh. naturw. Verein. Bremen, 33, 211-241.
]Report from the Bremen bird collections: additions to an
article by Gustav Hartlaub frmn April 1896 in this journal.]
Duncker, H. & Dewers, E 1931/32. Festschrift zum 75.
Geburstag des Herrn Prof. Dr. C. A, Weber. Bremen: Natur-
wissenschaftlicher Verein zu Bremen. [A festschrift for C
A Weber on Moors• Heathlands, Geology, Palaeobiology]
Duncker, H. & Lange, E 1934, Neue Ziele und Wege
des Biologieunterrichts. Vier Beitrage, Frankfurt Main:
Diesterweg. [New objectives and ways of teaching biolo-
gY]
Meyer, H. & Duncker, H. 1933. Von der Verhtitung un-
werten Lebens: ein Zyklus von 5 Vortragen. Bremen:
G.A.v. Halem. [The Prevention of Unworthy Life]
