A Magyar Természettudományi Múzeum évkönyve 60. (Budapest

i
The Evolutional Significance of Aberrations Appearing in
the Plumage of the Crossbill (Loxia curvirostra Linnaeus)
By L.
HORVÁTH,
Budapest
The results obtained from the examination of aberrations displayed by a number
of passerine and piriform bird species have now been augmented by another one.
The crossbill (Loxia curvirostra) exhibits a wide range of differences not only as to
age and sex but also with respect to colouration and pattern. Most of these are not
aberrational in nature but represent individual variations, a special characteristic
of this species. The orange reddish, red, reddish brown hues and their manifold
transitional tinges — the mosaic-like pattern — of the males are generally known.
However, the females are also rather varying, and the basic tonality of the plumage,
from light yellow through yellowish and greyish green to brownish green, shows a
gamut of individual variations. I n my experience, this variability appears to a certain
rate even in the young birds, though less conspicuously than in the adult specimens.
The extensive variability refers, however, only to the basic hue, one may also
say, the fundamental colour of the birds. The pattern proper is of a more constant
nature and, aside of the mosaic-like construction owing to molting, no individual
aberrations can be observed even in the contrasty pattern of the longitudinally
arranged spots of the young specimens. The wellnigh unlimited variability of the
basic hue against the conservativism of the pattern is so striking that it must inevi­
tably raise the interest of the research worker.
I cannot but see the further justification of my aberrational investigations,
conducted on numerous bird species in the past, in the results obtained by the study
of aberrations displayed in the pattern of the crossbill. I n the evaluation of the aber­
rations established on this interesting bird, I am satisfied to see a supplementation
of my researches made in various and systematically rather removed groups of the
passeriform or song-birds. Aside of this order, I succeeded to reveal the presence
of aberrations also in species of various genera relegated to the Piciformes which
surrendered indisputable evidences to the descent of the species in question and the
disentangling of their relationships.
The aberrations found in the pattern of the crossbill corroborate anew the validity
of this line of investigations. The extension of earlier findings to the bird under dis­
cussion will also render new informations on the postglacial resettling of Europe.
These were the considerations which led me, in examining the atavistic aberra­
tional features of the crossbill, to refer to earlier results with respect to other species
and to point out that the present contribution is but an intermediate link of studies,
began some years ago and indubitable extensible to also other taxa in the future.
Thus the study of the aberrations of the crossbill is also hereby fitted into the scope
of a wide investigational program and all results obtained will be interpreted in
connexion with the scientific data heretofore gained from the previous examination
of other bird species.
After the delineation of the course of investigation, let us now see our approach
with respect to the crossbill. First of all, some short and generalized statements should
be made. Despite the fact that the genus Loxia has an enormous distribution and
ranges beyond the Palaearctic and Holarctic Regions even into the Oriental and
indeed the Neotropical Regions, it is extremely homogeneous, that is, it comprises
species showing but relatively slight deviations as regards size, shape, and colour
(not hue!). The main character of the pattern in the plumage is similar or nearly
identical in all three known species, regardless of age and sex. The young birds of
all three species are greyish and longitudinally lined in the lower part of the body;
the females show a yellowish hue and hardly any pattern, whereas the males display
various hues of red.
The crossbill (Loxia curvirostra) — our species under investigation — has an
extensive range and splits up into a number of subspecies. A sketchy distribution
involves Europe, NW Africa, Asia Minor, the Caucasus, Turkestan, Mongolia, Japan,
West China, the Himalaya, South Annam and the northern part of Luzon ; in America
it occurs from the southern part of Alaska and from South Canada and New Foundland southwards, through Southern California and the Bay of Mexico to Nicaragua.
Recent investigations list 11 subspecies in the Old, and 7 in the New World.
The distinct specific state of the parrot crossbill, the second species of the genus
Loxia (L. pytiopsittacus B O R K H A U S E N ) , is not recognized by all students even today.
A critical analysis of this state of affairs will be made later, at the present I merely
wish to sketch up its area. The taxon inhabits Scandinavia and the neighbouring
territories, ranging in the north to the Ural and from here through Minsk and Poland
to East Germany and Denmark. As a vagrant, it appears- also in England, Yugoslavia,
and Western Siberia.
Finally, the third and last member of the genus is the twobarred crossbill
(Loxia leucoptera G M E L I N ) . again of a most extensive range, inhabiting not only
the Holarctic Region but nesting in America even in the mountains of Hispaniola
in the West Indian islands. With respect to this enormous range, it is more than
striking that only the population nesting in Hispaniola was up to now regarded as a
distinct subspecies (Loxia leucoptera megaplaga R I D G E W A Y ) . The subspecies elegáns,
described by H O M E Y E R from Siberia, shows a hardly tenable variation in hue
against the nominate form, hence the majority of investigators deny its validity.
The species curvirostra, subdivided into a host of subspecies, is phylogenetically
doubtless younger than the almost monotypical leucoptera, since the characteristics
still show a rather loosened state. The justification of this statement is to be found in
a number of previous papers of mine discussing other species, hence I confine myself
to a mere restatement of the fact.
For the time being, I aver, with respect to the realtionship of the two securely
distinct species (curvirostra and leucoptera), that the essential element of the differ­
ence between them appears in the pattern of the upper portion of the wing. Mani­
festly, therefore, if atavistic features in the younger species (curvirostra) are to be
sought for, attention should be centered on the alar pattern.
In the course of my studies, I succeeded to examine a considerable number of
exemplars of the respective species and subspecies, — of a bird not easy to collect.
Prior to estabhshing and evaluating the atavistic aberrational features, I submit the
data of my research material. I n the collection of the Zoological Museum of the
Humboldt University, Berlin, I found 192 specimens ; in the Museum für Tierkunde,
Dresden, and the Natural History Museum, Budapest, I examined 116 exemplars.
The 308 crossbill specimens showed a rather good distribution with respect to species,
subspecis, and locality of collecting. Of them, 248 belonged to Loxia curvirostra, 28
to Loxia pytiopsittacus, and 32 to Loxia leucoptera. I have worked in Dresden in
1965, in Berlin in 1966, and the material of the Budapest museum was examined in
1967.
Listing only the more important data, the material examined was as follows :
Loxia
Loxia
Loxia
Loxia
Loxia
Loxia
Loxia
Loxia
Loxia
Loxia
Loxia
Loxia
Loxia
Loxia
Loxia
Loxia
Loxia
Loxia
Loxia
Loxia
curvirostra
curvirostra
curvirostra
curvirostra
curvirostra
curvirostra
curvirostra
curvirostra
curvirostra
curvirostra
curvirostra
curvirostra
curvirostra
curvirostra
curvirostra
curvirostra
curvirostra
curvirostra
curvirostra
curvirostra
curvirostra LINNAEUS, 131 i n d . ( 6 9 çf, 3 4 9 2 7 j u v . 1 pull.)
estiae P I I P E R & HARMS, 2 i n d . (çf, $)
scotica H A R T E R T , 2 i n d . (çf, $ )
pusilla GLOGER, 1 i n d . (çf)
minor L I N D E R & C . L . B R E H M , 4 i n d . (çf )
meridionalis R O B E R T S & KLEINSCHMIDT, 1 i n d . (çf)
himalayensis B L Y T H , 2 2 i n d . (5 çf, 5 $ , 1 2 j u v . )
poliogyna W H I T A K E R , 6 i n d . (2 çf, 1 9 , 3 j u v . )
altaiensis SUSHKIN, 5 i n d . (4 çf, 1 9 )
japonica R I D G E W A Y , 1 4 i n d . (6 çf, 1 Q, 1 j u v . )
albiventris SWINHOE, 21 i n d . (9 çf, 10 9 > 2 j u v . )
tianschanica LAUBMANN, 7 i n d . (2 çf, 3 Q, 2 j u v . )
ermaki KOZLOVA, 7 i n d . ( 2 0*, 2 9 > 3 J - )
balearica H O M E Y E R , 2 i n d . (1 çf, 1 j u v . )
caucasica B U T U R L I N , 2 i n d . (juv.)
stricklandi R I D G E W A Y , 5 i n d . (2 çf, 3 9 )
luzonensis GRANT, 7. i n d . (3 Q*, 1 9» 3 j u v . )
guillemardi MADARÁSZ, 7 i n d . (4 çf, 2 j u v . , 1 pull.)
bangsi GRISCOM, 2 i n d . (çf)
americana WILSON, 2 i n d . (çf 9 )•
U V
Of the 20 above subspecies of Loxia curvirostra, not all are valid today, but I
still list them under these names since it is thus that I found them in the Berlin and
Dresden Museums, and also because I do not intend to go into the problems of subspecific separation resting on morphological characteristics. The first of the above rea­
sons is justified insofar as later workers, or those interested in the problem, can thus
better find the specimens in question. As for the second one, I omit the synonymic
problems and their critical review for the fact that they are based without exception
on differences in hue-and not in pattern! — and measurements of the bill, features
which have no reference to the present, atavistic aberrational investigations. Inci­
dentally, the morphologico-microsystematical separations all rest on rather uncertain
grounds, as for instance in the case of Loxia curvirostra estiae. This taxon was namely
drawn in under Loxia pytiopsittacus: Also this instance substantiates my own stand­
point, common with numerous other research workers, namely that Loxia pytiopsit­
tacus is not a distinct species but only a subspecies of Loxia curvirostra. As will be
seen below, and as I have referred to above, I found atavistic aberrational specimens
as well among the pytiopsittacus as the curvirostra specimens, and more than that,
even in approximately the same percentage ( !)
My research material of the two other taxa was as follows:
Loxia
Loxia
Loxia
Loxia
Loxia
pytiopsittacus BORKHAUSEN, 2 8 i n d . ( 1 2 çf, 12 9 , 4 j u v . )
leucoptera leucoptera G M E L I N , 18 i n d . ( 1 0 çf, 5 9> 3 j u v . )
leucoptera bifasciata C . L . B R E H M , 1 2 i n d . (4 çf, 6 Ç , 1 j u v . )
leucoptera elegáns H O M E Y E R , 1 i n d . (çf)
leucoptera megaplaga R I D G E W A Y , 1 i n d . ( 9 )
Subsequent to the above introduction of the material examined, I propose to
discuss in details the specimens displaying atavistic aberrational features. First how-
ever, it should be clarified to which features in the pattern can an atavistic signifi­
cance be attributed.
As was stated above, both sexes and also the juvenile specimens of the species
belonging to the genus Loxia show extensive variability with respect to hue and
pattern (more precisely, to the mosaic-like design) of the coverts. The mosaic pattern
of especially the males varies almost continually or rather contiguously from the
feathered fledgeling state to the sexually mature adult age. However, this widescaled variability refers only to the pattern exhibited by the converts, or more exactly
to the transitional period between the fledgeling state and sexual maturity. The wing
and tail feathers, and their tectrices are constant to the highest degree.
An excellent example in the substantiation of this statement is that the plumage
of even the youngest specimens of either the crossbill (L. curvirostra) or the parrot
crossbill (L. pytiopsittacus) reveals, even in traces, the light transverse stripes char­
acteristical of the upper wing coverts of the two-barred crossbill (L. leucoptera).
this feature very conspicuously even in the very youngest plumage. Hence, if a like
vittation were to be found in either curvirostra or pytiopsittacus of any age or sex,
it could not but be regarded as an atavistic abnormality.
Such abnormalities were in fact found on 33 curvirostra and 3 pytiopsittacus
specimens of my research material. This represents 7.5% of the examined 248 curvi­
rostra individuals, and 9.3% of the 28 pytiopsittacus exemplars. And with due respect
to the fact that not all workers accept the specific distinctness of pytiopsittacus, the
criticism of which contention is outside of the scope of this paper, then 36 of the
investigated specimens displayed the above atavistic aberrational feature, in other
words, 7.7 per cent of the birds was abnormal from the point of view of evolutional
investigations. As related to the inferences drawn from my findings involving similar
studies on a considerable number of species, this fact implies that the species (or two,
if pytiopsittacus were to prove to be distinct) is already beyond the stage of flourishing
specific separation, and the merely one kind — and also observable on essentially
less than 10 per cent of the specimens — of atavistic abnormalities indicates a rather
substantial stabilization of the characteristics.
Although morphological systematics recognizes today yet a great number of
subspecies, my investigations tend to show a termination of the process of segregation,
since the differentiating characters, namely the hardly fixable connotations as to
hue and the differences in size and measurements of the bill (rendered utterly indis­
tinct by the many transitions), fail to characterize in a convincing and satisfactory
way even the subspecies considered as still distinct.
Whereas the variational series based on the clines can be well established in a
number of other species embracing also numerous subspecies (e.g. in the case of
Emberiza citrinella), no traces of it can be detected as regards the crossbills, a fact
which further weakens the demonstrative force of the differentiating characteristics
of the recently valid subspecies.
The present atavistic aberrational studies have pointed out that the species
leucoptera is the older one at the same time evincing also the age of the one (or two)
species (if pytiopsittacus be regarded as dinstinct) descending from it, and testifying
more on the convergence rather than the divergence of the characters. The morpho­
logical analysis, resting often on rather subjective characters, can be substituted by a
synthesis founded on objective, evolutional features.
The above conclusions should yet be substantiated by a detailed, investigational
analysis. To this end, the atavistic aberrational specimens shall now be taken one
by one, and the nature of the observed evolutional features discussed in details for
all 36 specimens. The starting point to this is evidently a precise description of the
pattern appearing on the upper wing coverts of the species L . leucoptera.
The two-barred crossbill has, as implied in its name, two conspicuous, white
cross-bands on the wing. The tip of the greater upper wing-coverts has a wide white
zone with a very fine, pale rosy shade; this is the distal stripe. The proximal one
consists of the confluent white spots on the end of the median and lesser wingcoverts. The two stripes are confluent because the visible section of the median wingcoverts is wholly white, while the lesser ones covering them are white only at the
tips, and this latter also tends to a pinkish hue.
Prior to the thorough discussion of the 36 atavistic aberrational specimens, I
again wish to emphasize that I am unable to see justified the distinctness of Loxia
curvirostra and L . pytiopsittacus, and thus join the camp of those who consider the
latter as but a subspecies of the former. My standpoint is further strengthened by
W I T H E R B Y ' S renowned book, the Handbook of British Birds, in which he contends
that the subspecies Loxia curvirostra scotica H A R T E R T is transitional between curvi­
rostra and pytiopsittacus, and if proofs will be forthcoming that the nominate form
(Loxia curvirostra curvirostra) also nests in Scotland, then Loxia curvirostra scotica
will have to be regarded as the parrot crossbill ( Loxia pytiopsittacus ) :
My studies disperses the uncertainties deriving from morphological systematics
by reason of an evolutional foundation, since I found 3 atavistic aberrational speci­
mens among the 28 examined pytiopsittacus individuals, which means 9.3 per cent.
And there were, among the 248 curvirostra exemplars, only 33 aberrational ones,
that is, 7.5 per cent. The sum total, as I pointed out above, is 36 aberrational indivi­
duals among the 276 birds, that is, 7.7 per cent. This implies that the revertal to the
species Loxia leucoptera shows equal rates for both L . curvirostra and L . pytiopsittacus.
The 33 atavistic specimens of Loxia curvirostra are as follows :
1. L . curvirostra çf, Samhof, L i v l a n d . A very narrow, white bar on the t i p o f the
primaries.
2. L . curvirostra j u v . rf, Heidelberg. Traces o f a bar on the t i p of the primaries.
3. L. curvirostra çf, P a t á r a Cemi, East Borschomi, Anti-Caucasus, 6 March, 1963.
Traces o f a bar on the t i p o f the primaries.
4. L . curvirostra j u v . rf, Kloster, Hiddensee. 3 N o v . , 1956. Traces o f a bar on the end
of the primaries.
5. L . curvirostra rf Samhof, L i v l a n d . 18 Jan., 1898. A narrow, distinct bar on the t i p o f
the primaries.
6. L . curbirostra j u v . rf, Germany. A narrow bar on the end o f the primaries.
7. L . curvirostra çf, Hellenorm, L i v l a n d , 18 Jan., 1890, A narrow bar on the end of the
primaries.
8. L . curvirostra çf, Samhof, L i v l a n d . Traces o f a bar on the end o f the primaries.
9. L . curvirostra j u v . çf, Samhof. L i v l a n d . Traces o f a bar on the end o f the primaries.
10. L. curvirostra luzonensis çf, Benguet, Irisan. 25 June, 1903. A narrow, distinct bar
on the end o f the primaries.
11. L . curvirostra himalayensis, çf, Lachen, 2700 m.a.s.l, Sikkim, 4 N o v . , 1938. A
narrow, white bar on the end o f the primaries.
12. L . curvirostra himalayensis, 9> Koman-dse, South Tetung Range, 2 May, 1929. T w o
distinct b u t narrow bars ; one on the end of the primaries, the other on the tips o f the
secondaries.
13. L . curvirostra himalayensis, j u v . çf, N o r t h Kansu, China, 5 May, 1930. T w o narrow,
white bars, on the end o f the primaries and secondaries, respectively.
14. L . curvirostra himalayensis j u v . çf, Lan-kau, N o r t h Kansu, 2 Febr., 1930. Two weak
bars, on the end o f the primaries and the secondaries, respectively.
15. L . curvirostra albiventris j u v . çf, Darasun, China, 5 N o v . , 1866. A narrow, white bar
on the end o f the primaries.
16. L. curvirostra tianschanica çf, K a r a k o r u m , Himalaya, Kashmir, 26 March, 1904.
A narrow white bar on the end o f the primaries.
a
17. L. curvirostra japonica Ç , Lau-ku-kou, N o r t h Kansu, 2 3 Jan., 1 9 3 0 . Traces o f a
white bar on tbe end o f the primaries.
18. L. curvirostra çf, Sweden, N o v . , 1 9 0 0 . Traces o f a w h i t e bar on the end o f the
primaries.
19. L. curvirostra cf, K u r o v , Czechoslovakia, 2 3 N o v . , 1965. A narrow b u t distinct bar
on the end o f the primaries.
20. L. curvirostra japonica cf, Yehol, Sechuan, China, 2 7 A p r i l , 1916. A narrow, w h i t e bar
on the end o f the primaries.
21. L. curvirostra çf, Spas Demensk, Smolensk, 2 3 D e c , 1942. A narrow, white bar on
the primaries.
22. L. curvirostra albiventris, cf, Japan. A rather wide, w h i t e stripe on the end o f the
primaries.
23. L. curvirostra albiventris cf, Japan. Traces of a white bar on the end of the primaries.
24. L. curvirostra albiventris cf, Japan. A strikingly wide, w h i t e stripe on the end o f the
primaries.
25. L. curvirostra albiventris çf, I s s y k - k u l , China. December. Two strikingly wide, w h i t e
stripes on the end o f the primaries and secondaries, respectively.
26. L. curvirostra bangsi j u v . çf, Sinnig, N o r t h Kansu, China, 2 4 A p r i l , 1 9 3 0 . T w o
conspicuous, narrow bars, on the end o f the primaries and secondaries, respectively.
27. L. curvirostra çf, Frauenau an Rassel, Germany, 2 9 March, 1 9 1 3 . Traces o f t w o
white bars on the end o f the primaries and secondaries, respectively.
28. L. curvirostra çf, Madarasi H a r g i t a , Transyslvania, Rumania, 2 9 March, 1 9 4 2 .
Three conspicuous white stripes of a slightly rosy t i n t on the end o f the primaries,
secondaries, and tertiaries, respectively. I t was specimens like these t h a t BONAPARTE
& S C H L E G E L described as the new subspecies L. curvirostra rubrifasciata i n 1850, and
C. L . B R E H M as a new species L. rubrifasciata i n 1853.
G Y . MADARÁSZ mentioned that A. K O C Y Á N also shot a similar specimen at
Oravitz (Com. Árva, now is Czechoslovakia) on 7 February, 1884, and that it found
its way to V. TASCHUSI'S collection. Again, MADARÁSZ reported on a like specimen
from the old collection (consumed by fire in 1956) of the Hungarian National Museum ;
the exemplar originated also from the Comitat Árva. According to literature, I .
M E D R E C Z K Y observed similarly coloured crossbills near Ungvár in 1895. Quoting
B R E H M , I . C H E R N É L considered the individuals captured by K O C Y Á N and M E D R E C Z K Y
as representing a subspecies of the two-barred crossbill (Loxia leucoptera), and named
them pink-winged crossbill.
W I T H E R B Y mentions on the one hand that a pale wing stripe caused by a lighten­
ing of the primary apices is a general occurrence in the crossbill, and on the other
that the pinkish discolouration of the tertiary apices is also a general phenomenon in
the winter plumage of old males. At the same time, ha states unequivocally and
categorically that two or three light bands never occurs in curvirostra.
With due attention to, and in the knowledge of, the above discussion, and on
the basis of my own studies based on a large and extensive material, I must contend
that even a single wing bar, but especially a double one, cannot be anything else but
an atavistic aberrational feature and therefore an evidence that L . curvirostra des­
cended from L . leucoptera. The single stripe occurring in curvirostra is by no means
general, because I observed it only in 33 (7.5 per cent) of 248 exemplars, though I
listed as aberrational even those, as witnesses the list above, which showed merely
traces of the feature in question.
The research material contained numerous juvenile specimens with their early
plumage, indeed there were also some pulli, but not even these latter exhibited the
least traces of a white bar. Of the conspicuous three stripes, observed on specimen
No. 28, the tint of the proximal one, namely the rosy discoloration on the apices of
the tertiaries, agrees with the normal winter colouration as given by W I T H E R B Y , but
the other two indubitably represent leucoptera features. I t is quite clear also from the
examples given up to now that the features representing abnormal revertals occur in
a clear state only on very few specimens, presumbaly on less than one per cent of the
cases. Most of the aberrational specimens display no more than one, more or less
developed, wing bar.
I n the followings, I submit 5 further female specimens, on which I also found
similarly atavistic aberrational features, though there is no known literature data
referring to any such "individual" aberration in the colour pattern.
29. L . curvirostra albiventris 9, N a r y n , Turkestan, 13 J u l y . A distinct, narrow, white bar
on the t i p o f the primaries.
30. L . curvirostra
9> Zetelaka, M t . Hargita, Transylvania, Rumania, 2 9 March, 1 9 4 2 .
Two distinct, narrow, white bars on the tips of the primaries and secondaries, re­
spectively.
31. L . curvirostra japonica 9> Japan, 1 9 0 0 . A distinct white stripe on the end of the
primaries.
32. L . curvirostra albiventris j u v . 9 > Issyk-kul, China. E n d of March. A distinct, narrow
bar on the end o f the primaries, and the traces of one on the end of the secondaries.
3 3 . L . curvirostra himalayensis j u v . sex? Sungpan-ting, Sechuan, China, 11 June, 1 9 1 4 .
A distinct, narrow bar on the end of the primaries.
Finally, I submit the data of the three pytiopsittacus specimens proved to be
atavistic among the 28 examined birds.
1. Loxia pytiopsittacus çf, Sarkau, Kurische Nehrung. A very weak, w h i t i s h bar on the
end of the primaries.
2. L . pytiopsittacus çf, Sweden, 4 A p r i l , 1 8 9 1 . A distinct, narrow, whitish bar and the
traces of a similar one, on the end of the primaries and the secondaries, respectively.
3 . L . pytiopsittacus j u v . çf, Neustrelitz, 1 9 6 4 . A distinct, narrow, w h i t i s h bar on the
t i p of the primaries.
To sum up, we can safely state that the atavistic features, demonstrable on the
species of the genus Loxia, contradict on the one hand the distinct specificity of the
two taxa, Loxia curvirostra and L . pytiopsittacus, and substantiate on the other the
scientific hypothesis that L . curvirostra descended from L . leucoptera. Lioxia curvi­
rostra is already well past the flourishing stage of specific differentiation, it had stabi­
lized to a great extent, and therefore all subspecific segregations based on differenc­
es in hue and in measurements of the bill are founded on rather uncertain grounds.
As shown by my investigations, this widely ranging species is strikingly homogeneous
despite its extensive individual variability. I t seems probable that its vagrant nature
and its nesting in the most divers times and localities are the indirect causes to which
the extensive variability, shown in overall hue and the size of the bill, should be
asribed. I n spite of all this apparent variability, the evolutional studies based on the
atavistic aberrations evince the remarkable homogeneity of the species. The ecological
conditions of the crossbills also testify to this end. With respect to food, the method
of acquiring it, nesting conditions, and the feeding of the fledgelings, and as regards
yet many other traits, the species of the genus Loxia are so uniform that hardly
can any other similar instance be found in other genera.
My sincere thanks are due to Dr. W. GÖTZ, Director of the Museum für Tierkun­
de, Dresden, and to G . M A U E R S B E R G E R , Keeper of the Ornithological Collection of
the Zoological Museum, Humboldt University, Berlin, for their cordial help in making
available the rich and priceless research materials at their disposal.
References: 1. C H E R N É L , I . : M a g y a r o r s z á g madarai (Budapest, 1 8 9 9 , p . 6 1 8 — 6 2 1 ) . —
2. H A R T E R T , E . : Die Vögel der p a l ä a r k t i s c h e n Fauna (Berlin, 1 9 1 0 — 2 1 , p. 1 1 6 — 1 2 4 ,
Z u s ä t z e und Berichtigungen, p . 2 0 6 0 — 2 0 6 2 ) . — 3 . M A D A R Á S Z , G Y . : M a g y a r o r s z á g ma­
darai (Budapest, 1 8 9 9 — 1 9 0 3 , p .
19 — 21, 1 6 5 - 1 6 6 ) .
— 4. W I T H E R B Y , H . F . ,
Handbook of B r i t i s h Birds ( 1 , London, 1952, p . 9 3 - 1 0 2 ) .
etc.:
The