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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 123. No. 3. September 2011 
~95% of avian species diversity. We can Find no 
previous reports of this phenomenon in wild bird 
species, nor any bird species outside of the Order 
Galliformes. Triorchidism in birds was First 
reported by McFarland (1965), who examined 
>2,000 male Japanese Quail and found one case 
of triorchidism that was associated with absence 
of the right kidney. In that case, the right testis 
was divided into two nearly co-equal sections, 
both of which were undergoing normal spermato¬ 
genesis. Katiyar et al. (1986) First reported a 
supernumerary right testis in a Domestic Chicken. 
Shrivastava et al. (1988) subsequently reported a 
Domestic Chicken with a supernumerary left 
testis that was severely reduced in size (less than 
10% the size of the left and right testes) and 
~1 cm posterior to the caudal end of the left 
testis, ventral to the third lobe of the left kidney. 
The small round supernumerary testis was softer 
in consistency, and normal in color and spermato- 
genic activity by histological examination. 
Hocking (1992) systematically examined the 
testes of 378 male Domestic Chickens and found 
three cases of triorchidism, each of which was 
comprised of two left testes. The two left testes in 
two of the three cases were nearly co-equal in size 
with normal semen quality and testis histology. 
The smaller of the two left testes in the third case 
was much less than half the volume of the larger 
one and was characterized by strongly reduced 
spermatogenesis. Hocking (1992) suggests that 
supernumerary testes probably originate by con¬ 
genital defect and are fairly common in domestic 
fowl, as indicated by his Finding prominent third 
testes in 0.8% of males. Supernumerary testes 
originating by congenital defect should be present 
throughout life, in contrast to asymmetrical testes, 
which are known to shift in relative size according 
to age, season, overall condition, and other, 
unidentiFied factors (Moller 1994. Kimball et al. 
1997. Graves 2004). 
We examined and measured testes in 591 male 
hummingbirds representing 65 species during 
Fieldwork between 2006 and 2010. including 21 
male Great-billed Hermits (MSB and CORB1DI 
specimen data). We observed only one case of 
triorchidism (0.17% of male hummingbirds ex¬ 
amined), suggesting the phenomenon is signifi¬ 
cantly less common in wild hummingbirds than in 
domestic fowl, although the small sample size of 
triorchid individuals prohibits statistical testing. 
The paucity of case reports of supernumerary 
testes in birds makes it difficult to understand the 
mechanisms or risk factors that may be associ¬ 
ated with this condition. However, —100 cases 
of triorchidism in humans have been described 
(Hassan et al. 2008), and the developmental, 
pathological, and functional aspects of human 
triorchidism are useful for understanding avian 
triorchidism. Approximately two-thirds of human 
supernumerary testes occurred on the left side as 
in the triorchid hummingbird, and a slightly 
smaller proportion (63%) have reproductive 
potential as evidenced by normal spermatogen¬ 
esis (Spranger ct al. 2002. Bergholz and Wenke 
2009). Leung (1988) classified cases of polyor- 
chidism into four types, of which the triorchid 
hummingbird seems to Fit into 'type C\ which is 
characterized by the supernumerary testis having 
its own epididymis and sharing the ductus 
deferens with the regular testis in a parallel 
fashion. This configuration is thought to occur 
due to incomplete longitudinal division of the 
genital ridge and the proximal portion of the 
mesonephric duct during development (Singer et 
al. 1992). 
Two cases of triorchidism have been observed 
in a rare Malagasy tortoise, Geochelonc yniphora 
(Mourgue 1989), suggesting the phenomenon 
occurs in at least three deep amniote lineages. 
The present case is the first report for a wild bird 
and the first for any bird outside of the Order 
Galliformes. The hummingbird species involved, 
the Great-billed Hermit, is a promiscuous, lek- 
mating species and is expected to be under 
selection for sperm volume and quality (Birkhead 
1998). It is not known whether this evolutionary 
pressure may be associated w ith susceptibility to 
presumed congenital defects such as the supernu¬ 
merary testis observed. Investigators performing 
autopsies on birds should look for and report 
supernumerary testes to help elucidate the phylo¬ 
genetic distribution and evolutionary implications 
of this interesting phenomenon. 
ACKNOWLEDGMENTS 
We thank Miguel Campos Diaz. Jessica A. Castillo. Ben 
Cook. Silvio Flores Flores. Zachary R. Hanna. Oliva* D 5 *' 7 
Idrogo. Andrew B. Johnson, Todd Mark. Came MeAlee. 
Christopher Mcrkord, Redinson Rodriguez Salazar. EV>ra 
Stisanibar. Thomas Valqui, and Doug Whalen for assistance 
with field and laboratory work. We thank the citizen 1 - and 
leaders of the community of Sianbal for access to Held sites 
Funding was provided in part by NSF DEB-0543556 i*> J 
A. McGuire and Robert Dudley. We are grateful to 
1NRENA for providing permits (087-2007-INRENA- 
IFFS-DCB). 
