Body and organ weights, and carcass composition of breeding female
W hite-winged Scoters
P A T R IC K W . B R O W N a n d L E IG H H . F R E D R IC K S O N
Introduction
M any studies o f breeding waterfowl have
focused on changes in body weight during
reproduction because the tem poral sequence
and m agnitude o f these changes indicates the
w ay each species m eets reproductive dem ands.
B ody weights provide an approxim ate index of
m etabolic reserves. W eight changes during the
reproductive season have been docum ented for
m any waterfowl (e.g. W eller 1957; Milne 1976;
A nkney and M aclnnes 1978; K rapu 1981;
A nkney 1984; K rapu 1981; A nkney 1984;
T om e 1984 and H ohm an 1986). T he general
p attern is one of increasing body weight before
laying and of declining weight through laying
and incubation. This study was conducted to
determ ine how body and organ weights, and
carcass com position change during reproduc­
tion in fem ale W hite-winged Scoters Melanitta
fusca deglandi.
Study A rea and M ethods
A dult fem ales w ere collected on G ordon (N =
18) (52°53'N , 107°22'W ) Iroquois (N = 2 ). and
B ram ble lakes ( N = l) , and on Lac 1a Peche
( N = l ) , Saskatchew an, and Jessie Lake (N =
13) (54° 25'N , 110° 75'W , A lberta), 1978-80.
N o m ore than 10% o f the pairs on each lake
w ere collected each year. Scoters w ere assigned
a breeding status corresponding to 8 categories.
T hese categories were: (1) prelaying - slow
follicle grow th. Largest follicle less than 10 m m ,
oviduct slightly o r m oderately enlarged, (2)
rapid follicle grow th - largest follicle 10 mm or
larger, enlarged oviduct, no evidence of egg
laying, (3) laying - fem ales in the early and
m iddle stage o f laying. Largest follicle over 10
m m , ruptured follicles present, but at least 4
follicles yet to be ovulated (as judged by size),
(4) term inal laying - n ear the end of egg laying.
R uptured follicles present, with no m ore than 3
follicles to be ovulated, (5) early incubation 0 —2 days after initiating incubation, d eter­
m ined by candling the eggs (W eller 1956), (6)
m id-incubation - 10—14 days into the incuba­
tion period, (7) late incubation - 24 o r more
days into the incubation period, and (8) brood
rearing.
B ody and organ weights w ere recorded
within four hours after collection. Internal
organs, sternal muscles, and entire carcasses
w ere weighed to the nearest 0.1 g on a triple
beam balance. C ontents of the digestive tract
w ere rem oved. Birds w ere then frozen for later
analysis. F or the com position analysis, most
feathers w ere rem oved by using a commercial
sheep shear; rem aining feathers w ere plucked
by hand. E ntire carcasses (minus ova larger
than 14 mm because these w ere thought likely
to be ovulated) were hom ogenized by passing
through a food grinder at least 6 times (smallest
sieve size 4 m m ). Small ova that were unlikely
to be ovulated (ie. < 1 4 m m ) w ere left in the
carcass because they could supply energy or
protein needs later upon resorption. The
hom ogenate was mixed after each passage
through the grinder, and any skin or bone that
had been trapped on the grinder blade was
rem oved and blended with it. A random
sam ple o f the hom ogenate weighing about
10% o f the bird's weight was rem oved for
analysis p e rfo rm ed by the U niversity of
M issouri A gricultural E x p erim en t Station
Chem ical Laboratories. Petroleum ether Soxhlet extraction of lipid determ inations and
K jeldahl p rocedures for nitrogen content
according to A O A C standard procedures
(H orw itz 1970) w ere used. Percent moisture
was determ ined by placing the sample in a
vacuum oven at 1(X)°C for 15 hours. Estim ates
o f ash w ere obtained by placing dried samples
in an oven and holding the tem perature at
550°C for 2 hours. D uplicate samples were
subm itted to verify results.
B ecause of small sam ple sizes, differences
betw een reproductive periods were investi­
gated using a M ann-W hitney U test (Conover
1971). T he level o f significance for all tests was
alpha = 0.05.
R esu lts
B o d y w eights
B ody w eights o f fem ales at th e
arriv al a re u n k n o w n , b u t th re e
p rela y in g fe m ales w ere co llected
21st a n d 27th M ay. o n ly a w eek
tim e o f
o f th e 5
b etw een
a fte r the
103
104
Patrick W. B row n a n d Leigh H. Fredrickson
Table 1. Mean body and selected organ weights for female White-winged Scoters in relation to
breeding status. Collections were made in central Saskatchewan, 1978-80. W eights (g) shown are the
m ean ± standard e rro r, except for brood rearing.
C ategory
B ody weight
Eviscerated
body w eight“
O rgan weights
G izzard
Small intestine
Liver
Oviduct
O va and ovary
Pectoral muscleb
N um ber o f birds
Prelaying
R apid
follicle
growth
Laying
1441 ±42
1458 ±25
1452 ±23
1242±38
1236±26
1211 ±17
Stage of incubation (days)
Terminal 1
laying
0-2
10-12
24+
Brood
rearing
1408 ±20
1316 ± 4 0
1205 ±26
1091 ± 42
1096
1190+12
1162±35
1082 ±26
966 ±33
968
3 5 .3 ± 3 .0 30.0 ± 1.9 26.4 ± 1.3 25.9± 1.8 2 1 .0 ± !.7 21.0+0.5
19.0±2.5
60 .0 ± 4 .8 5 2 .4±1.2 49.1 ± 4 .6 46.6±5.5 46.0 ± 3 .3 31.7± 4.4 39.5± 3.3
56 .0 ± 1 .5 53.3 ± 1.0 4 5 .3± 3.0 41,8 ± 2 .4 42.2 ± 2 .0 33.1 ± 5 .6 3 5.7+ 4.9
3 .7 ± 0 .9 22.1 ± 4 .0 35.1 ± 2 .2 38.3±5.3
9 .0 ± 0 .9
2 .0+ 0.3
1.5±0.2
3 .3 ± 0 .9 2 7 .8±4.2 49 .0± 3.2 31.3±4.7
1.5±0.9
0.5 ± 0 .2
2.1 ± 0.3
137.4±4.7 140.4 ± 1.9 138.7±4.2 141.1 ± 2 .5 140.6±3.4 1 3 0 .0 ± 4 .1 111.8+4.0
5
8
5
4
3
4
5
18.5
43.2
38.2
1.2
1.7
103.0
1
aB ody w eight minus all internal organs except kidneys.
bIncludes left pectoralis, supracoracoideus, and coracobranchialis muscles.
p e a k arriv al p e rio d . M ean w eight o f th ese
fem ales w as 1514 g (ran g e 1472—1560 g),
a n d th e ir m ean e v isc e ra te d b o d y w eight
(i.e . b o d y w eig h t w ith all in tern al org an s
re m o v e d ex c ep t k id n ey s) w as 1303'g (ran g e
1243—1351 g ), th e h eav ie st w eight rec o rd ed
in th e b re e d in g seaso n .
B o d y w eig h t a n d th e ev iscerated body
w eight (E B W ) re m a in e d co n sta n t until
b e tw e e n te rm in a l laying a n d early in cu b a­
tio n , w h e n th e y d e c lin e d sig n ific an tly
(P < 0 .0 5 ) (T a b le 1). B ody w eight declin ed
rap id ly d u rin g in c u b a tio n , m ostly from d e ­
clines in th e E B W a n d re p ro d u c tiv e tra ct.
C h an g e s in su b c u ta n e o u s fa t reserv e s a re
p ro b a b ly b e st reflected in th e E B W (T ab le
1) w hich w as g re a te st d u rin g p relay in g and
th e n d eclin e d to a low a t th e en d o f incu­
b a tio n . D u rin g egg laying, body w eight
d eclin ed a b o u t, E B W acco u n tin g fo r 52%
(74 g) o f this re d u c tio n . O f th e w eight lost
d u rin g in c u b a tio n , 87% (196 g) o ccu rred in
th e E B W .
Carcass C om p o sitio n .
L ipid levels d id n o t vary significantly from
p relay in g th ro u g h to th e term in al laying
stag e, b u t th e lipid level d u rin g rap id follicle
grow th w as significantly g re a te r (P < 0 .0 5 )
th an th a t in th e early in cu b atio n level
(T ab le 2). D u rin g in cu b atio n lipid levels
d e c lin e d a b o u t 3 .4 3 g /d a y . P r o te in
r e m a in e d c o n s t a n t u n til th e d e c lin e
(P < 0 .0 5 ) b e tw een term in al laying an d early
in cu b atio n (T a b le 2). A tro p h y o f th e ovi­
d uct an d ov ary p ro b ab ly acco u n ted fo r m ost
o f this. P ro te in levels d eclin ed (P < 0 .0 5 )
from term in al laying to th e en d o f in cu b a ­
tio n ; th e g re a te st d ecline o c cu rred betw een
early an d m id -in cu b atio n w hen fem ales
w ere m ost a tte n tiv e to th e ir n est an d had
greatly re d u c e d feed in g tim e (B row n 1981 ).
W eight loss o f th e liver, sm all in te stin e, an d
stern al m uscles o ccu rred rap id ly durin g
in cu b atio n (T ab ic I)
A sh c o n te n t w as significantly g re a te r
Table 2. Carcass composition (g) of female White-winged Scoters collected during the breeding
season. W eights shown arc m eans ± standard error.
Stage
Prelaying
Rapid follicle growth
Laying
T erm inal Laying
Early incubation
M iddle incubation
Late incubation
Brood rearing
W ater
Lipid
Protein
Ash
923± 14
896± 16
875 ± 18
904±41
824 ±24
780± 18
732± 17
773
138+28
175 ± 16
167±22
129±37
145± 10
92 ±23
49± 19
27
337± 12
337 ± 6
332±6
343+4
304 ± 5
285 ± 7
274+ 6
280
65 ± 3
65 ± 2
69 ± 5
8 2±6
60±7
64 ± 5
No. of
birds
5
8
68±8
5
3
4
4
5
71
1
Scoter weights an d com position
(P < 0 .0 5 ) d u rin g th e te rm in al laying p e rio d
th an in any o th e r b reed in g cate g o ry (T ab le
2). L evels in all o th e r c ateg o ries w ere
sim ilar. W a te r c o n te n t o f fem ales declin ed
(P < 0 .0 5 ) b etw een p rclay in g an d laying,
term in al laying a n d e arly in c u b a tio n , an d
early in cu b atio n to late in cu b atio n .
D iscussion
T he p a tte rn o f w eight ch an g e in W hitew inged S co ter fem ales is difficult to in te r­
p re t b ecause little in fo rm atio n is available
fo r th e w interin g p e rio d . T h e m ean fo r 15
fem ales (B ellro se 1980) w as 1179 g, and
N elson and M artin (1953) re p o rte d a m ean
w eight o f 1125 g fo r 19 fem ales. T h e ages
an d d ates o f co llection fo r th e se b ird s w ere
u n k n o w n , alth o u g h th ey w e re p ro b ab ly
killed d u rin g th e fall an d w in te r hu n tin g
seasons. T h e m ean w eight o f 10 ad u lt
fem ales collected d u rin g w in te r in K achem ak B ay, A la sk a, w as 1732 g (ra n g e 1566—
1946 g) (S an g er an d Jo n es 1981), an d tw o
ad u lt fem ales from P rince W illiam S o u n d
w eighed 1577 a n d 1480 g on 18 F eb ru a ry
a n d 24 M arch , 1978 (D . V . D e rk se n , P ers,
co m m .). T h ese w eights are sim ilar to those
in o u r earliest co llected fe m ales, suggesting
th a t fem ales are at o r n e a r th e ir heaviest
w eight u p o n arriv al a t b re e d in g a reas.
T h e lack o f change in b o d y w eights
b efo re and d u rin g egg laying suggests th a t
fem ales m et m ost o f th e ir n eed s th ro u g h
th e ir diet. D eclines in body w eight d u rin g
in cu b atio n suggest th a t fem ales th e n relied
upon e n d o g e n o u s reserv es in p a rt to m eet
energy n eed s. D u rin g laying an d incu­
b atio n , fem ales lost a b o u t 25% o f th e ir
m axim um b o d y w eight. F em ales n e a r th e
en d o f incu b atio n h ad th e low est w eights
rec o rd e d d u rin g th e study. O n e b ro o d re a r­
ing fem ale co llected a b o u t 4 days a fter
h a tch , also h ad an ex trem ely low w eight.
Fem ale E u ro p e a n E id e rs S. m . m o ltis­
sim a at F o rv ie , S c o tla n d (M iln e 1963)
d eclined as m uch as 30% in w eight from egg
laying to th e e n d o f in cu b atio n . C o m m o n
E id ers S. m . dresseri in Q u e b e c and M aine
lost m o re th an 30% o f th e ir b o d y w eight
d u ring laying an d in cu b atio n (C a n tin et al.
1974, K orschgen 1977).
W eight losses in v ario u s m uscle tissues
have been re p o rte d fo r sev eral species o f
w ildfow l, an d m ay result from th e use o f
tissue p ro tein to su p p o rt m etab o lic an d egg
105
laying n eed s, from a ch an g e in d ie t, o r from
b o th . C h an g es in th e d ie t o f W hite-w inged
S coters from bivalves o n w in terin g a reas
(e.g . G ro sz an d Y ocom 1972; S an g er an d
Jo n es 1982; V e rm e e r an d B o u rn e 1982) to
so ft-b o d ied in v e rte b ra te s on b reed in g a reas
m ay be resp o n sib le fo r th e declin e in
gizzard an d o th e r digestive o rg an w eight,
becau se gut m o rp h o lo g y is k now n to vary
w ith volum e o f fo o d e a te n an d w ith fibre
c o n te n t (M iller 1975; A n k n ey 1977). A fte r
in cu b atio n b eg an , th e declin e in digestive
o rg an w eight p ro b a b ly re su lte d from a
c o m b in atio n o f tissue p ro te in use a n d lesser
co n su m p tio n o f fo o d . T h e to tal tim e sp en t
feed in g d u rin g in c u b a tio n p ro b a b ly in ­
c reased as in cu b atio n p ro g re sse d , becau se
fem ales w ere less a tte n tiv e in la te r stages of
in cu b atio n (B row n 1981). G re a te r feed in g
tim e n e a r th e e n d o f in c u b a tio n m ay
acco u n t fo r th e o b serv ed increase in sm all
in testin e w eight.
W h e re fe m a le W h ite -w in g e d S c o te rs
o b ta in e d th e ir lipid re serv e is u n k n o w n ,
b e c a u s e n o b ird s w e re k n o w n to b e
c o lle c te d w ith in tw o w ee k s o f arriv al.
F em ales co llected in A p ril in K ach em ak
B ay, A la sk a, h a d low fat reserv es (S an g er
a n d Jo n e s 1982). A fte r arriv al, fem ales
sp en t 5 8 —62% o f th e ir tim e feed in g for
a b o u t th re e w eek s b e fo re in itiatin g egg
laying (B row n 1981). H o w e v e r, lipid levels
did no t ch an g e significantly until in cu b atio n
began.
S co ters u sed little o f th e ir p eak lipid
reserv e to lay th e ir eggs. T h e long egg laying
in terv al o f 1.43—1.60 day s p e r egg (K o sk i­
m ies an d R o u ta m o 1953; V e rm e e r 1969;
B row n an d B row n 1981) p ro b ab ly allow s
fem ales a d e q u a te feed in g tim e to acquire
n u trie n ts fo r egg fo rm a tio n (B ro w n 1981).
A lso , th e m ean w eight o f th e high q uality
in v e r te b r a te fo o d s c o n su m e d in c rea se s
a b o u t th e tim e egg laying begins (B row n
1981). T h ese facto rs m ay help fem ales
p reserv e th e ir en d o g en o u s reserv es fo r use
d u rin g in cu b atio n .
P ro te in an d lipid levels d eclin ed as in­
c u b atio n p ro g ressed , w ith m uch o f th e early
d e c lin e in p r o t e in a s s o c ia te d w ith
re so rp tio n o f th e re p ro d u c tiv e o rgans. B e­
tw een early an d late in c u b a tio n , declines in
ste rn al m uscle w eight a n d p ro te in levels
m ay have resu lte d from th e use o f tissue
p ro tein to p ro d u c e en erg y . L ipid levels
d ro p p e d m ark ed ly d u rin g in cu b atio n as
th ey w ere used to m e e t en erg y needs.
E n d o g e n o u s lipid reserv es seem m ost im-
106
Patrick W. B row n a nd Leigh H. Fredrickson
p o rta n t fo r p a rtially defray in g th e m e ta ­
bolic n eed s o f in cu b atin g fem ales. A b o u t
17% o f th e p eak lipid w eight w as e x p en d ed
d u ring egg laying, w h ereas 55% w as sp en t
d u ring in cu b a tio n . A s en d o g e n o u s reserves
a rc e x p e n d e d d u rin g in c u b atio n , so recess
tim e w as in c re a sed (B ro w n 1981). T ho u g h
m ost energ y an d n u trie n ts n e e d e d for laying
and in cu b atio n w ere o b ta in e d from th e d iet,
e n d o g en o u s reserv es m ay have play ed an
im p o rta n t ro le in m eetin g daily energy
req u ire m e n ts d u rin g laying an d m ay be
neccssary for successful in cu b atio n .
Sum m ary
The weight and carcass com position of 35 breed ­
ing female W hite-w inged Scoters Melanitta fusca
deglandii from central Saskatchewan and eastcentral A lberta w ere determ ined. Body weights
were statistically sim ilar betw een prelaying and
laying, but declined 22.5% (P < 0.01) from the
end of laying to the end of incubation. W eight
loss resulted prim arily from absorption of the
ovary and oviduct at the end of laying, and the
use of fat and protein reserves during incubation.
Fem ale W hite-w inged Scoters relied upon their
diet to m eet m ost protein and energy require­
m ents during egg laying, whereas stored reserves
were needed most to defray energy needs during
incubation.
Acknowledgements
This project was funded by the Office of M igra­
tory Bird M anagem ent, U .S. Fish and Wildlife
Service C ontract No. USDI 1 4 - 1 6 - 0 0 0 9 - 7 7 ^
930. We are indebted to M .A . Brown for her help
with all aspects of the study. T.S. B askett, J.R .
Jones. J.E . Savage, and E .K . Fritzell gave help­
ful advice. C. Thom as, D . W hite, K. R autenstrauch, V. Cravens, J. Hodges, J. W are, and
W .D . Rundle helped in the field and laboratory.
J. Belz generously d o n ated equipm ent. R.
D erksen. M. H eitm eyer, D. Raveling, and K.
V erm eer provided helpful reviews of the m anu­
script. T hanks are also due G. Bogdan of the
CWS for providing the appropriate perm its. This
is a contribution from the Missouri Agricultural
Experim ent Station Projects, Projects 170 and
183, Journal Series 10019, G aylord Memorial
L aboratory (U niversity of M issouri-Colum bia
and M issouri D e p a rtm e n t o f C onservation
cooperating); and Missouri C ooperative Wildlife
Research U nit (U . S. Fish and Wildlife Service,
W ildlife M anagem ent Institute, Missouri D e­
partm ent of C onservation, and University of
M issouri-Colum bia cooperating).
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