297
ORNITOLOGIA NEOTROPICAL 11: 297–306, 2000
©
The Neotropical Ornithological Society
UROPYGIAL GLAND SIZE AND AVIAN HABITAT
Diego Montalti
1,2
& Alfredo Salibián
3
1
Cátedra de OrnitologÃa, Facultad de Ciencias Naturales y Museo,
Universidad Nacional de La Plata, Paseo del Bosque, 1900-La Plata, Argentina.
E-mail:
dmontalti@arnet.com.ar
2
Departamento de BiologÃa, Aves, Instituto Antártico Argentino, Cerrito 1248,
1010-Buenos Aires, Argentina.
3
CIC Buenos Aires and Universidad Nacional de Luján (Programa de EcofisiologÃa Aplicada),
6700-Luján (B), Argentina.
Resumen.
El papel fisiológico de la glándula uropigia es hasta ahora una controversia. Algunos autores afir-
man que su función podrÃa estar estrechamente vinculada con las propiedades hidrofóbicas de su secre-
ción, que puede ser esencial para impermeabilizar el plumaje. Por consiguiente podrÃa esperarse que el
grado de desarrollo de esta glándula debe ser mayor en aves acuáticas que en especies terrestres. Con el
objeto de validar esta hipótesis, se determinó el peso de la glándula (GW) relativo al peso corporal (BW)
expresando los resultados como porcentajes (GW x 100/BW). Se analizaron los datos de 1164 individuos
de 126 especies de aves adultas de 49 familias. Los resultados mostraron la ausencia de una clara correla-
ción entre el Ãndice calculado y el grado de contacto de las aves con el agua. No se observó correlación
filogenética derivada de la presencia de la glándula uropigia.
Abstract.
The physiological role of the uropygial gland is still controversial. Certain authors state that its
function could be closely connected to the hydrophobic properties of its secretion, that may be essential
for plumage waterproofing. Therefore, it could be hypothesized that the degree of this gland's develop-
ment should be greater in aquatic birds than in terrestrial species. In order to validate that hypothesis,
gland's mass (GW) relative to body weight (BW) was determined, expressing the results as percentages
(GW x 100/BW). Data of 1164 adult individuals from 126 bird species from 49 families were analysed.
Results showed the absence of a clear cut correlation between the calculated index and the degree of birds'
contact with water. No phylogenetic correlation was observed derived from the presence of the uropygial
gland.
Accepted 15 June 2000.
Key words: Uropygial gland, habitat, aquatic birds, terrestrial birds.
INTRODUCTION
The uropygial gland, may be considered as the
only organized tegumentary structure of
external secretion typical of birds, is always
found in embryonic stages, while in adults of
some species it may be vestigial or absent
(Rheidae, Psittacidae and Columbidae)
(Johnston 1988). It is a holocrine gland that
secretes a complex and variable mixture of
substances formed greatly of aliphatic
monoester waxes, formed of fatty acids (with
various degree of methyl branching) and
monohydroxy wax-alcohols. However, some
types of diester waxes containing hydroxyfatty
acids and/or alkane-diols exist in the secre-
tions of the uropygial gland of some groups
of birds (Jacob & Ziswiler 1982, Downing
1986, Jacob 1992) and is highly specialized in
lipid synthesis (Kolattukudy & Rogers 1978,
Urich 1994).
Morphological descriptions of the gland
298
MONTALTI & SALIBIÃN
of different taxa and systematic classifications
based on its morphology and chemical nature
of secretory lipids have been reported (Jacob
& Ziswiler 1982, Johnston 1988). Informa-
tion on the uropygial gland's histology, secre-
tion chemistry, and possible physiological
functions has been recorded (Elder 1954,
Lucas & Stettenheim 1972, Jacob & Ziswiler
1982, Montalti
et al
. 1994). It is interesting to
mention that Jacob
et al
. (1979) demonstrated
sexual differences in the chemical composi-
tion of the secretion in domestic ducks. The
extirpation of the uropygial gland did not
reveal any serious consequence for the sur-
vival of pigeons (Montalti
et al
. 1999), hens,
and passerine birds (Jacob 1976).
The physiological function of this gland
has not been studied extensively. Many work-
ers hold that this gland's function is closely
connected with the hydrophobic properties
of its secretion, which would have an essential
role in plumage waterproofing. It is also pos-
sible that the gland could play a role in plum-
age hygiene against microflora and/or in
supplying provitamin D and repository and
excretory function for several pesticides and
pollutants (Johnston 1975, 1976, 1978, Jacob
& Ziswiler 1982, Quay 1986, Kozulin & Pav-
luschick 1993, Pilastro
et al
. 1993, Jacob et al.
1997, Gutiérrez
et al
. 1998, Bandyopadhyay &
Bhattacharyya 1996, 1999). We undertook
this study in order to check this point of view.
Our hypothesis was that adult birds‘gland
size, considering its weight relative to the
body weight, should be related to the bird’s
habitat, being relatively greater in species that
are in permanent or temporary contact with
water than in terrestrial species.
MATERIALS AND METHODS
Data used in this work came from two
sources. Some of them were taken from Jacob
& Ziswiler (1982) and Johnston (1988). Most
of them came from measurements carried out
at our laboratory between 1985 and 1995. In
the latter case, birds were captured in differ-
ent places of the Buenos Aires province,
Argentina; penguins (Spheniscidae), petrels
(Procelariidae and Hydrobatidae), cormorants
(Phalacrocoracidae), sheathbills (Chionidae)
and skuas (Stercorariidae) came from King
George Island (South Shetland Islands) and
from Laurie Island (South Orkney Islands),
Antarctica. A few samples were provided by
the La Plata Zoo.
Some 1164 individuals from 126 species
and 49 families were studied in total. Body
weight was determined in the field or at the
laboratory, using a dynamometer balance (± 1
g accuracy); glands were removed according
to the technique developed by Montalti
et al
.
(1998) and weighed with an electronic balance
(± 0.01 g accuracy). These values were used
to calculate the gland's mass as percentage in
relation to body weight (GW x 100/BW) for
each one of the considered species. Follow-
ing Johnston’s procedure (1988), data were
grouped in families and a mean gland weight
(as %) for each species was calculated. When
the number of data was higher than two,
results were expressed as means ± SD; other-
wise individual values were shown. Data were
evaluated statistically by one-way analysis of
variance and the Tukey test.
RESULTS AND DISCUSSION
The Appendix shows the results ordered
according to the systematic sequence of
Morony
et al
. (1975). We found the largest
mean relative gland weight in the Sternidae
(S
terna trudeaui
, mean = 0.522), Podicipedidae
(
Podylimbus podiceps
, 0.418–0.556) and Procel-
lariidae (
Daption capense
, mean = 0.426). These
findings are coincident with those of Jacob &
Ziswiler (1982) and Johnston (1988) who also
found the largest gland’s weight in other spe-
cies of the same families.
Among the Passeriformes, the greatest
299
UROPYGIAL GLAND SIZE AND HABITAT
relative weights were recorded in the Furnari-
idae (
Phacellodomus striaticollis
, mean = 0.363),
Tyrannidae (
Serpophaga subcristata
, mean =
0.359), and Emberizidae (
Poospiza nigrorufa
,
0.280–0.320). Kennedy (1971) and Jacob &
Ziswiler (1982) recorded the largest value in
Passeriformes in Troglodytidae (
Troglodytes tro-
glodytes
, 0.561 and 0.580) whereas, in a larger
sample of
Troglodytes aedon
, we found a much
lower value (mean = 0.245).
The smallest glands proportional to body
weight were found in Ardeidae (
Bubulcus ibis
,
mean = 0.014), and in Columbidae (
Columba
picazuro
, mean = 0.016). Other authors
(Kennedy 1971, Jacob & Ziswiler 1982,
Johnston 1988) have reported similar results
in Columbidae. The small size of the gland in
these families may be attributed to the pres-
ence of the powder down; it is known that
some birds such as herons, pigeons and kagus
possess a rudimentary preen gland whose
function may be fulfilled by powder down
(Jacob 1976). Thus, the well developed pow-
der down production may explain their
reduced uropygial glands or absence of it
(Johnston 1988).
In this study, it came out that there was
no clear cut correlation between gland's size
and the bird's exposure to water. It is
accepted that species that plunge into the
water to capture their prey would require
larger glands than species that pick their prey
from the water surface, almost without con-
tact with water (see Jacob & Ziswiler 1982).
However, the relative gland weight appeared
without a clear relationship with the degree
of aquaticity of the considered species. In
spite of their condition of being fully aquatic
species, the relative size of Sternidae resulted
one of the largest among the species we stud-
ied; similar findings were reported by
Johnston (1988) for
S. albifrons
.
On the other hand, birds living in aquatic
environments not always have a more devel-
oped gland than non-aquatic birds. If we
compare the size of glands of aquatic vs land-
birds, it will come out that both show compa-
rable values in spite of their different habitats;
for instance,
Anas georgica
(mean = 0.306) vs
Guira guira
(mean = 0.296);
Pygoscelis adeliae
(mean = 0.159) vs
Colaptes campestroides
(mean
= 0.174).
When comparing the gland size among
landbird species, we found great variability.
That is the case of fully terrestrial species as
Zonotrichia capensis
(mean = 0.198),
Milvago chi-
mango
(mean = 0.143),
Athene cunicularia
(mean = 0.090) and
Zenaida auricularia
(mean
= 0.026). On the other hand, it is interesting
that if we compare the glands’size of aquatic
species, but of dissimilar degree of aquaticity,
it can be noted the existence of peculiar dif-
ferences.
Pygoscelis papua,
which is a pursuit
diving species, has a gland size of 0.132 %,
while in
Daption capense
, a surface filterer bird,
the size is 0.426 %. The size of the glands of
these seabirds seems to be in the opposite
direction of the expected values, i.e., the
gland size of
P. papua
might be larger than the
gland of
D. capense
because their feeding
behaviour involves a different degree of con-
tact with water. A similar trend is observed
when the comparison between freshwater
species is done; that is the case of
Fulica
rufifrons
(mean = 0.168) and
Anas versicolor
(mean = 0.342).
Several authors have reported differences
in relative gland weights, attributing them to
seasonal variations (Kennedy 1971), habitat
(Jacob & Ziswiler 1982), body weight
(Johnston 1979), individual variation, and sex
(Johnston 1988). In our case, no difference
was found in the gland relative size between
males and females.
Analysis of birds' phylogenetic classifica-
tion (according to Morony
et al
. 1975) shows
that despite the fact that the number of our
samples may be considered small, the trend
of the development of the gland was inde-
pendent from the lineage of the birds. Thus,
300
MONTALTI & SALIBIÃN
the uropygial gland is present in birds phylo-
genetically distant (Tinamidae-Hirundinidae)
or, on the contrary, absent in phylogenetically
close taxa (some Psittacidae and Colum-
bidae).
In summary, if we assume that the gland's
mass constitutes a valid parameter to quantify
its degree of gland development, our results
indicate that the physiological role of the
gland does not depend upon gland mass.
Chemical composition of the secretion may
be involved in this (Jacob 1978). The role
could be more complex than a feather water-
proofing function.
There is no evidence that glands of simi-
lar mass produce comparable quantities of
secretion. Consequently, we cannot disregard
the possibility that the degree of contact with
water might rather be associated with adap-
tive changes in the composition of the secre-
tion, involving the biosynthesis routes of the
gland's lipids.
ACKNOWLEDGMENTS
This work was supported by grants from the
Universidad Nacional de La Plata (Programa
de Incentivos). D.M. is affiliated to the Cáte-
dra de FisiologÃa Animal, FCNyM-UNLP.
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APPENDIX. Uropygial gland weight relative to body mass (gland weight x 100/ body weight). Data as
percentage (mean ± SD). Species listed according to Morony
et al
.(1975).
FAMILY/Especies
1,2
Mean
SD
n
3
TINAMIDAE
Rhynchotus rufescens
Nothura maculosa
SPHENISCIDAE (A)
Pygoscelis papua
Pygsocelis adeliae
Pygoscelis antarctica
GAVIIDAE (A)
Gavia stellata
**
Gavia immer
**
PODICIPEDIDAE (A)
Podilymbus podiceps
Rollandia rolland
PROCELLARIIDAE (A)
Macronectes giganteus
Daption capense
Halobaena caerulea
HYDROBATIDAE (A)
Oceanites oceanicus
Fregetta tropica
PELECANIDAE (A)
Pelecanus occidentalis
**
FREGATIDAE (A)
Fregata magnificens
**
PHALACROCORACIDAE (A)
Phalacrocorax olivaceus
0.080
0.141
0.132
0.159
0.217
0.190
0.103
0.418-0.556
0.428
0.191-0.437
0.426
0.212-0.332
0.445
0.459
0.373
0.067
0.279
0.017
0.042
0.015
0.042
0.070
0.016
0.009
—
0.107
—
0.047
—
0.055
0.079
0.045
0.005
0.066
6
41
10
16
6
3
3
2
10
2
5
2
16
5
3
3
6
302
MONTALTI & SALIBIÃN
APPENDIX. Continuation.
FAMILY/Especies
1,2
Mean
SD
n
3
Phalacrocorax bransfieldensis
Phalacrocorax georgianus
ANHINGIDAE (A)
Anhinga anhinga
**
SULIDAE (A)
Sula bassana
*
ARDEIDAE
Syrigma sibilatrix
Egretta alba
Egretta thula
Bubulcus ibis
Nycticorax nycticorax
CICONIDAE
Ciconia maguari
Ciconia ciconia
THRESKIORNITHIDAE
Plegadis chihi
Platalea ajaja
PHOENICOPTERIDAE
Phoenicopterus chilensis
ANHIMIDAE
Chauna torquata
ANATIDAE (A)
Dendrocygna viduata
Cygnus melanocorypha
Coscoroba coscoroba
Chloephaga picta
Cairina moschata
Anas flavirostris
Anas georgica
Anas versicolor
Netta peposaca
CATHARTIDAE
Coragyps atratus
**
ACCIPITRIDAE
Elanus leucurus
Rostrhamus sociabilis
Circus buffoni
Buteo magnirostris
FALCONIDAE
Polyborus plancus
Milvago chimango
Falco sparverius
PHASIANIDAE
Gallus gallus
0.154
0.191-0.194
0.152
0.350
0.025
0.029
0.029
0.014
0.031-0.041
0.051-0.074
0.077-0.082
0.208
0.148-0.190
0.181
0.063
0.263
0.152
0.234
0.063-0.095
0.242
0.382
0.306
0.342
0.408
0.043
0.094
0.097
0.065
0.044
0.060
0.143
0.082
0.094
0.041
—
0.017
—
0.006
0.006
0.013
0.007
—
—
—
0.043
—
0.043
0.016
0.035
0.012
0.057
—
0.065
0.066
0.120
0.108
0.134
0.004
0.015
0.020
0.013
0.011
0.018
0.033
0.022
0.041
3
2
5
2
4
7
8
3
2
2
2
31
2
12
3
8
3
4
2
5
8
9
5
4
4
3
11
4
4
6
17
6
3
303
UROPYGIAL GLAND SIZE AND HABITAT
APPENDIX. Continuation.
FAMILY/Especies
1,2
Mean
SD
n
3
ARAMIDAE
Aramus guarauna
RALLIDAE (A)
Aramides ypecaha
Pardirallus maculatus
Pardirallus sanguinolentus
Gallinula chloropus
Gallinula melanops
Fulica armillata
Fulica rufifrons
GRUIDAE
Grus canadensis
**
JACANIDAE (A)
Jacana jacana
ROSTRATULIDAE
Nycticryphes semicollaris
RECURVIROSTRIDAE
Himantopus himantopus
CHARADRIIDAE
Vanellus chilensis
SCOLOPACIDAE
Tringa flavipes
Calidris fuscicollis
CHIONIDAE
Chionis alba
STERCORARIIDAE (A)
Catharacta maccormicki
Catharacta antarctica
LARIDAE (A)
Larus dominicanus
Larus cirrocephalus
Larus maculipennis
STERNIDAE (A)
Sterna trudeaui
RHYNCHOPIDAE (A)
Rynchops niger
**
ALCIDAE (A)
Uria algae
*
Alca torda
*
COLUMBIDAE
Columba livia
Columba picazuro
Columba maculosa
Zenaida auriculata
Columbina picui
0.141
0.114
0.294-0.342
0.281-0.316
0.222
0.296
0.111-0.219
0.168
0.045
0.157
0.191
0.088
0.096
0.231
0.251
0.202
0.211
0.172
0.174
0.232
0.225
0.522
0.200
0.170
0.220
0.026
0.016
0.022
0.026
0.069
0.020
0.020
—
—
0.033
0.091
—
0.048
0.009
0.032
0.017
0.006
0.023
0.031
0.036
0.029
0.053
0.049
0.058
0.043
0.042
0.031
—
—
—
0.012
0.005
0.006
0.010
0.016
4
6
2
2
6
4
2
4
4
6
3
4
51
8
22
6
17
35
13
6
23
3
6
2
3
50
9
7
26
5
304
MONTALTI & SALIBIÃN
APPENDIX. Continuation.
FAMILY/Especies
1,2
Mean
SD
n
3
PSITTACIDAE
Melopsittacus undulatus
Ara macao
Nandayus nenday
Cyanoliseus patagonus
Myiopsitta monachus
CUCULIDAE
Guira guira
TYTONIDAE
Tyto alba
STRIGIDAE
Asio flameus
Athene cunicularia
Bubo virginianus
**
APODIDAE
Apus apus
*
TROCHILIDAE
Chlorostilbon aureoventris
ALCEDINIDAE (A)
Chloroceryle americana
RAMPHASTIDAE
Ramphastos toco
PICIDAE
Colaptes campestroides
Colaptes melanolaimus
Melanerpes carolinus
**
FURNARIIDAE
Cinclodes fuscus
Furnarius rufus
Phacellodomus striaticollis
Schoeniophylax phryganophila
Anumbius annumbi
Lessonia rufa
TYRANNIDAE
Machetornis rixosus
Tyrannus savana
Tyrannus melancholicus
Pitangus sulphuratus
Pyrocephalus rubinus
Serpophaga subcristata
Serpophaga nigricans
Satrapa icterophrys
Xolmis coronata
Hymenops perspicillatus
PHYTOTOMIDAE
Phytotoma rutila
0.207
0.057-0.097
0.084
0.094-0.117
0.094
0.296
0.121
0.068-0.089
0.090
0.038
0.050
0.286-0.288
0.415-0.510
0.065-0.071
0.174
0.108
0.117
0.223
0.125
0.363
0.309
0.240
0.121
0.150
0.103
0.104
0.124
0.143
0.359
0.248
0.089-0.178
0.053-0.083
0.161
0.111
0.023
—
0.004
—
0.033
0.111
0.033
—
0.028
0.004
—
—
—
—
0.021
0.027
0.02
0.033
0.045
0.083
0.049
0.094
0.020
0.007
0.032
0.045
0.037
0.046
0.183
0.083
—
—
0.022
0.023
5
2
3
2
12
35
3
2
10
4
7
2
2
2
10
11
3
11
29
5
5
9
3
5
19
8
25
7
3
4
2
2
4
10
305
UROPYGIAL GLAND SIZE AND HABITAT
APPENDIX. Continuation.
FAMILY/Especies
1,2
Mean
SD
n
3
HIRUNDINIDAE
Phaeoprogne tapera
Tachycineta leucorrhoa
MOTACILIDAE
Anthus hellmayri
TROGLODYTIDAE
Troglodytes aedon
POLIOPTILIDAE
Polioptila dumicola
MIMIDAE
Mimus saturninus
Mimus triurus
TURDIDAE
Turdus rufiventris
Turdus amaurochalinus
Turdus migratorius
**
EMBERIZIDAE
Sicalis flaveola
Zonotrichia capensis
Paroaria coronata
Poospiza nigrorufa
Donacospiza albifrons
Embernagra platensis
Cardinalis cardinalis
**
ICTERIDAE
Molothrus bonariensis
Molothrus badius
Molothrus rufoaxilaris
Icterus cayanensis
Agelaius thilius
Pseudoleistes virescens
Sturnella superciliaris
FRINGILLIDAE
Carduelis magellanicus
Serinus canarius
STURNIDAE
Sturnus vulgaris
**
CORVIDAE
Corvus corax
*
Corvus corone
*
Pica pica
*
Cyanocitta cristata
**
PARIDAE
Parus major
*
Parus ater
*
0.076
0.125
0.257
0.245
0.153
0.134
0.074
0.129
0.064-0.093
0.100
0.101
0.198
0.093
0.278-0.323
0.366-0.620
0.275
0.083
0.116
0.262
0.143
0.140
0.212
0.246
0.242
0.122
0.151-0.186
0.117
0.120
0.100
0.090
0.127
0.140
0.150
0.016
0.032
0.043
0.067
0.085
0.026
0.017
0.027
—
0.014
0.028
0.084
0.022
—
—
0.079
0.009
0.042
0.076
0.012
0.013
0.054
0.051
0.056
0.032
—
0.009
—
—
—
0.052
—
—
6
4
3
13
9
9
3
3
2
3
5
35
4
2
2
26
3
6
27
3
3
31
13
27
16
2
3
6
8
5
3
12
11
306
MONTALTI & SALIBIÃN
APPENDIX. Continuation.
FAMILY/Especies
1,2
Mean
SD
n
3
AEGITHALIDAE
Aegithalos caudatus
*
ESTRILDIDAE
Padda oryzivora
PLOCEIDAE
Passer domesticus
0.210
0.111-0.136
0.171
—
—
0.061
2
2
22
1
(A) means aquatic bird.
2
Asterisks indicate the source of information: * = from Jacob & Ziswiler (1982), ** = from Johnston
(1988).
3
n = number of specimens of each species.