SUMMARY
The trachea of the male Hooded Merganser is from 3 1/2 to 8 inches shorter, and much narrower, than that of the male American Merganser, Red-breasted Merganser, or Smew. It possesses but one dilation, this being in the posterior quarter. The trachea of the male Red-breasted Merganser also has a single dilation, but it is much larger than in the Hooded Merganser and is just anterior to the midpoint of the trachea. In the male American Merganser there
are two dilations. In the male Smew there is none. The tympanum, which is present in the male in all four species discussed, varies in configuration and dimensions. In the Hooded Merganser it differs decidedly in proportions and in the number of fenestrae from that of the Smew; and while somewhat similar in shape and number of openings to those of the American Merganser and the Red-breasted Merganser, it is but half as large. The trachea of the female Hooded Merganser is shorter and smaller than in the female American Merganser, Red-breasted Merganser and Smew. In all these species, however, the trachea of the female is much the same.
INCLUDING A COMPARISON WITH THE TRACHEAE OF CERTAIN OTHER
MERGANSERS
MONG the many gaps in our knowledge of the Anatidae, as pointed out
by Delacour and Mayr (1945: 34), are those regarding the tracheae of
certain species. The following description of the trachea of the Hooded Mer-
ganser (Lophodytes cucullatus) will supplement both the first account written
by William MacGillivray (1852: 227) and a later brief account by John C.
Phillips (1926: 249).
Prepared, unstretched adult male Hooded Merganser tracheae used in this
study had an overall length (including the tympanum) of 102 to 138 mm. This
wide variation is at least partly the result of using both alcoholic and dried
specimens for measurement. A dried trachea is shorter. (This is very likely be-
cause of shrinkage caused by the disappearance of the membrane between the
osseous rings.) Even when measuring fresh material, a variation in results is
possible. For example, one fresh female trachea when relaxed measured 110
mm., but when stretched to its fullest measured 155 mm. However, measure-
ments of the bony part of the structure are not affected by this shrinkage and
consequently show only slight variation. Furthermore, it is to be remembered
that discrepancies in total length measurements found in the literature may
be the result of age differences; of the condition of the specimen--whether
fresh, alcoholic, or dry; and/or of differences in measuring technique (i.e., over-
all length measurements may have been based on either a fully extended or a
contracted trachea).
For about three-quarters of its length the diameter of the tube in the male
Hooded Merganser varies little from of an inch (5 mm.). At the commence-
ment of its lower quarter it flattens and dilates to a width of about « inch (12
mm.). Joined to this enlargement by a short length of tube is an asymmetrical,
irregularly-shaped tympanum, a hollow, bony structure about as wide as long,
possessing two openings on the ventral and one on the dorsal side, each covered
by a tight membrane. The major protuberance (or chamber) is on the left
side. Two bronchi arise from the posterodorsal edge.
The tracheal rings are of several kinds. Most of those in the upper third of
the tube are complete and nearly uniform i width. All are of osseous tissue
and have little membrane between them. Those of the middle third also are
bony; some are complete, but most of them are tapered at the ends, and by a
The writer is greatly indebted to F. H. Kortright, E. B. Chamberlain, Jr., Philip Humph-
rey, and the Royal Ontario Museum of Zoology for furnishing the material on which this
description is based.
296
Elizabeth
B. Beard TRACHEA OF HOODED MERGANSER 297
regular staggered arrangement produce an interlocking or shingled effect. There
is very little membrane between these rings. The rings of the dilated, lower
third of the tube are tapered, staggered, and quite variable in width. They are
osseous on the ventral side but completely membranous on the dorsal side. The
approximately ten bony rings which connect the enlarged portion of the tube
with the tympanum are of peculiar structure. On the dorsal side they are flat
and somewhat tapered in width. On the ventral side, each ring becomes ex-
tremely narrow and rises to a small peak in the center. The 'peaks' of eight of
the ten rings form an acute midline carina. Membrane separates each of these
narrow rings ventrally.
Table 1 presents data on the tracheae of four male Hooded Mergansers.
The measurements of the tracheae of female Hooded Mergansers were from
TABLE 1
TRACHEAL MEASUREMENTS IN MILLIMETERS OF FOUR MALE HOODED MERGANSERS
Overall length, dorsal, from posterior edge of glot-
tis to posterior edge of tympanum
Overall length, ventral, from posterior edge of glot-
tis to posterior edge of tympanum
Diameter at base of glotlis
Diameter at narrowest part of tube
Diameter at beginning of dilation
Diameter between dilation and tympanum
Length of dilation
Greatest width of dilalion
Length of tympanum, dorsal
Length of tympanum, ventral
Greatest width of tympanum
Length of bronchi
Diameter of bronchi at base
1
(dried)
6
4
6
6
13
12
10
22
19
10
4
2
(dried)
89
102
6
4
5
5
13
11
9
21
20
3
(alcoholic)
98
109
6
4
5
5
13
12
9
21
20
13
3
(alcoholic)
124
138
6
4
6
6
13
12
10
21
20
24
4
TABLE 2
TRACHEAL MEASUREMENTS IN MILLIMETERS O1 THREE FEMALE HOODED MERGANSERS
Overall length from posterior edge of glot-
tis to posterior edge of simple tympa-
num
Diameter of tube
Greatest width of simple tympanum
Narrowest width of simple tympanum
Length of simple tympanum
Length of bronchi
Diameter of bronchi at base
1
(dried)
5
8
5
5
13
3
2
(dried)
107
5
8
5
5
13
3
3
(fresh)
110
5
8
5
5
13
3
Dec. 1951
298 THE WILSON BULLETIN Vol. 63, No. 4
one fresh and two dried specimens (Table 2). The overall length of the trachea
of a female Hooded Merganser is between 41 (107 mm.) and 42 inches (110
ram.). The tube is nearly uniform in diameter, averaging , of an inch (5 mm.).
The tympanum is a simple, symmetrical, hollow structure, roughly trapezoidal
in shape, about 6 of an inch (5 mm.) in length, and formed by fusion of the
tracheal rings. Two bronchi arise from its posterior aspect. The tracheal rings
are osseous and are quite uniform in size and shape, showing little tapering.
FIG. 1. Left, trachea of adult male Hooded Merganser, ventral aspect, shouting tympanum
at bottom. Middle, the tympanum, dorsal aspect. Right, trachea of adult female Hooded
Merganser, ventral aspect. All drawings a little under natural size.
Elizabeth
B. Beard TRACHEA OF HOODED MERGANSER 299
As an aid toward better understanding of the relationship of the monotypic
genus Lophodytes to the two other genera of Mergansers (Mergellus and Mergus),
a comparative review of the tracheae of Lophodytes cucullatus, Mergellus albellus,
Mergus merganser americanus, and Mergus serrator is herewith presented.
Measurements for these species (with the exception of the Hooded Merganser)
were obtained from published accounts and/or published natural-sized draw-
ings.
Male American Merganser (Mergus merganser americanus).--In the male
American Merganser the trachea is 10« inches long (Audubon, 1838: 270), 12
inches long (Yarrell, 1843: 296), or "about a foot in length, when moderate}y
extended" (MacGillivray, 1852: 209). It is, therefore, from five to eight inches
longer than in Lophodytes cucullatus. In the American Merganser, the tracheal
tube possesses two rounded enlargements, the first (maximum width: of an
inch) in the upper third of the tube, and the second (maximum width: x of
an inch) in the middle third of the tube. The lower third of the tube is of uni-
form width, with an average diameter of of an inch.
The tympana of the two species are similar in structure--both being hollow,
bony, of irregular shape, with the major protuberance on the left, and possess-
ing three membrane-covered fenestrae, one dorsal and two ventral. The great-
est diameter of the tympanum of the male American Merganser is 23 inches,
while that of the male Hooded Merganser is 3 of an inch. The bronchi arise
from the posterior edge on the dorsal aspect nearly one inch apart in the
American Merganser and about of an inch apart in the Hooded Merganser.
Female American Merganser.--The trachea of a female American Merganser
is 9 inches long, or about 46 inches longer than that of the female Hooded Mer-
ganser. Both have tracheal tubes of uniform size: « of an inch in the American
Merganser and of an inch in the Hooded Merganser. The simple tympanum
formed by fusion of the lower tracheal rings is of similar shape and structure
in both species. The bronchi stem from its posterior aspect, of an inch apart
for the American and - of an inch apart for the Hooded Merganser.
Male Red-breasted Merganser (Mergus serrator).--The trachea of the male
Red-breasted Merganser measures 11« inches (Audubon, 1849: 99), or about
11 inches (MacGillivray, 1852: 218); in other words between 5« and 7« inches
longer than that of the male Hooded Merganser. There is one enlargement just
above the midpoint of the tracheal tube. This dilation is two inches long and
of an inch wide. The male Hooded Merganser likewise has one dilation in
the tube but this is in the lowest quarter of the tube and is « of an inch wide
at its widest point and « of an inch long. In each species the diameter of the
remaining portion of the tracheal tube is quite constant, being between and
« of an inch wide in the Red-breasted Merganser and - of an inch wide in the
Hooded Merganser.
The tympanum of the male Red-breasted Merganser is irregularly heart-
shaped and has a maximum diameter of two inches. In the Hooded Merganser
Dec. 195l
300 THE WILSON BULLETIN Vol. 63, No. 4
this structure is asymmetrical and has a maximum diameter of a of an inch.
According to Latham (1798: 122) and MacGillivray (1852: 218), the tympana
of both species have three membrane-covered fenestrae, two ventral and one
dorsal; Audubon (1849: 99) mentions but "two lateral membranous spaces."
In the Red-breasted Merganser the bronchi arise of an inch apart on the pos-
terodorsal edge of the tympanum.
Female Red-breasted Merganser.--No exact measurements of the length of
the trachea were found, but since Audubon (1849: 99) states that the trachea
has 150 rings, the same number as in the female American Merganser (Au-
dubon, 1838: 270), the length is probably similar, i.e., about 9 inches long,
or about 4 inches longer than that of the female Hooded Merganser. The
tracheal tube is nearly uniform in diameter throughout and ends in a very sim-
ple symmetrical tympanum from the posterior aspect of which two bronchi
arise.
Male Smew (Mergellus albellus).--The trachea of the male Smew is about
nine inches long (Yarrell, 1843: 281; MacGillivray, 1852: 235) or from 3« to
5 inches longer than that of the male Hooded Merganser. The tube is narrow
(about of an inch) at the anterior end, but it gradually increases to a diameter
at midpoint of about of an inch, this being maintained for the rest of its
length. There is no dilation.
The tympanum of the male Smew possesses, according to Latham (1798:
124), one round fenestra covered by a drum-like membrane and, on the op-
posite side, a smooth, oval, hollow bone which is united with the membrane.
Yarrell (1843: 281) mentions "spaces in the bone supplied with tympanic
membranes." MacGillivray (1852: 235) states that there are "two lateral mem-
branes of which the posterior is largest." The drawing accompanying Bloch's
paper (1779, Tab. 18, Fig. 7) seems to show but one opening. The tympanum
is displaced to the left and measures 1 inches at its widest point and of an
inch long. The bronchi arise about « of an inch apart.
Female Smew.--No information was obtainable regarding the length of the
female Smew's trachea, but a life-size drawing of a portion of the trachea (Yar-
rell, 1843: 281) shows it to be uniform in width, with a diameter of 1'- of an
inch, the same as for the female Hooded Merganser. The simple tympanum
measures « by of an inch, that of the female Hooded Merganser by ,
of an inch. The bronchi arise ' of an inch apart in the Smew.
LITERATURE CITED
AUDBON, JOIN JAMES
1838 Ornithological biography. Vol. 4. Adam Black, Edinburgh.
1849 Ibid., Vol. 5.
BLOCH, M. E.
1779 Ornithologische Rhapsodien. Beschaftigungen der Berlinischen Gesellschaft
Naturforschender Freunde. Berlin.
DELACOUR, JEAN, AND ERNST MAYR
1945 The family Anatidae. Wilson Bulletin, 57: 3-55.
LATHAM, JOHN
1798 An essay on the tracheae or windpipes of various kinds of birds. Trans. Linn.
Soc. London, 4: 90-128.
MACGILLIVRAY, WILLIAM
1852 A history of British birds. Vol. 5. London.
PmLLIPS, JOIN C.
1926 A natural history of the ducks. Vol. 4. Houghton Mifflin Co., Boston.
3/4ARKELL, WILLIAM
1827 Observations on the tracheae of birds; with descriptions and representations of
several not hitherto figured. Trans. Linn. Soc. London, 15: 378-388.
1843 A history of British birds. Vol. 3. London.
UNIVERSITY OF MICHIGAN DEPARTIENT OF WILDLIFE MANAGEM. ENT ANN
ARBOR