Content uploaded by Beatriz Arroyo
Author content
All content in this area was uploaded by Beatriz Arroyo on Dec 16, 2014
Content may be subject to copyright.
J. Raptor Res. 30(4):224-233
¸ 1996 The Raptor Research Foundation, Inc.
AGE AND SEX DIFFERENCES IN MOLT OF
THE MONTAGU'S HARRIER
B.E. APd•O¾O • •'qt)J.R. KtNG
EGI, Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, United Kingdom
ABSTRACT.--Age and sex differences in the timing and pattern of feather molt in Montagu's harrier
(Circus pygargus) was studied in 184 museum specimens and live birds collected throughout their breed-
ing and wintering ranges. Molt in adults lasted 6-8 mo, starting in May-June in the breeding areas and
finishing in January-February on the wintering grounds. Apparently, Montagu's harriers do not suspend
molt during migration. Molt of primaries started earlier in adult females than in adult males, which was
probably related to their different roles in feeding nestlings during the breeding season, but both sexes
finished molt at about the same time. Yearlings started body molt on the wintering grounds and there
was a considerable discrepancy in the extent of body molt of yearlings between data obtained from skins
and those from live birds. Yearlings attained plumage similar to that of adults after the first complete
molt. Timing of flight feather molt in yearlings and second-yr males was similar to that of adults even
though they were not engaged in reproduction. Nevertheless, they finished molting earlier than older
birds, but this difference was not significant.
K•Y WOP, DS: Age and sex differences; Circus pygargus; Montagu's harri• molt phenology; molt rate.
Diferencias en la muda del aguilucho cerizo con respecto a la edad y al sexo
RESUM}•2q.--Se ha esmdiado el patr6n de muda en 184 aguiluchos cenizos (Circus pygargus) (fundamen-
talmente ejemplares en museos, y algunos individuos vivos), procedentes de todo su rango de distri-
buci6n, y se analizan las diferencias en fenologia de muda debidas a la edad y al sexo. La muda en los
adultos dura 6-8 meses, comenzando en mayo-junio en las zonas de crfa, y terminando en enero-
febrero en los cuarteles de invernada. Los datos disponibles sugieren que los aguiluchos cenizos no
suspenden la muda durante la migracitn. La muda de las primarias comienza antes en las hembras
adultas queen los machos adultos, lo que probablemente estf relacionado con la diferente contribucitn
de los sexos a la alimentacitn de los pollos, pero ambos sexos terminan mrs o menos al mismo tiempo.
Los individuos de primer ado comienzan la muda corporal en las fireas de invernada. Encontramos
divergencias importantes en el grado de muda corporal de los individuos de primer ado, entre los datos
procedentes de ejemplares de museo y datos procedentes de observaciones de campo. Se discuten las
posibles razones de esta divergencia. A1 final de la primera muda completa, los individuos de primer
ado adquieren un plumaje similar al de los adultos. E1 comienzo de la muda en los individuos de primer
ado yen los machos de segundo ado es similar a la de los adultos, aunque estos grupos de edad no se
reproducen. Sin embargo, parecen terminar la muda antes que los individuos de mrs edad, aunque las
diferencias no son significativas.
[Traduccitn de author]
Feather molt, reproduction, and migration are
three of the more energetically cosfly components
of avian life history. Molt is usually timed to mini-
mize peaks in energy demands during either re-
production or migration, and the duration and ex-
tent of molt is constrained by the energy invested
in either of the latter two factors (Pietianen et al.
1984). If there are differences between the sexes
Present address: CNRS/CEBC, Beauvoir Sur Niort,
F79360 France.
in their relative contributions towards breeding,
they may be reflected in sexual differences in molt.
Likewise, age-related differences in molt may be
expected between individuals that have not yet en-
tered the breeding population, and this should be
especially prominent in long-lived species with de-
layed sexual maturation.
Relatively little is known about molt in diurnal
birds of prey, when compared with that of other
bird orders. Large raptors such as eagles and vul-
tures do not undergo a complete molt every year,
224
DECEMBER 1996 MONTAGU'S HARRIER MOLT 225
but have several foci in the primaries where pri-
maries are molted sequentially (Stresemann and
Stresemann 1966, Houston 1975, Edelstam 1984,
Bortolotti and Honeyman 1985). In so doing, they
avoid excessive raggedness in the wings, which
would impair the lift necessary for flight. In con-
trast, small accipitrids such as hawks usually have
one complete molt a year, replacing the primaries
from the innermost to the outermost feathers, and
the secondaries from three foci (Miller 1941,
Piechocki 1955, Stresemann and Stresemann
1966).
The Montagu's harrier (Circus pygargus) breeds
throughout Europe (wintering in Africa) and the
Asian/Russian steppes (in the Indian subconti-
nent). The molt of Montagu's harrier has never
been previously described in detail. Here, we use
museum skins (collected throughout its range)
and field data from Madrid (Spain) and S•n•gal
(Africa) to describe the patterns of molt in this
species, the differences in timing and duration of
molt between males and females, and the acquisi-
tion of adult body and flight feathers by yearlings.
METHODS
Sources of Data. Data were recorded from 166 specimens
from the Natural History Museum, Tring, UK (28 female
yearlings, 31 male yearlings, 36 adult females, 71 adult
males), 10 skins from the Museum of Natural History,
Madrid (three adult females, seven adult males), three
skins of adult males from the Collection Hagi Botti, OR-
STOM Station, M'bour, S•n•gal, and five breeding birds
trapped alive in Madrid (two adult males, three adult fe-
males).
Field observations of yearlings in breeding areas in
Spain were also used for comparison. All yearlings could
be identified by the presence of uniformly dark second-
aries characteristic of juvenile Montagu's harriers. Males
change their iris color from brown to uniformly pale yel-
low before they are 3-4 mo old. Females do not attain
yellow irides until they are 3-4 yr old, although they
might have various degrees of yellow spotting before that.
We used eye color to sex birds in juvenile plumage when
possible.
Molt Scores. Molt of individual remiges and rectrices
was scored from 0-5, following Ginn and Melville (1983),
where 0 represents an old feather, and 5 a fully-grown,
new feather. The intermediate values (1-4) represent
progressions of feather growth. Throughout this study,
primaries are numbered from 1 (the innermost) to 10
(the outermost), and the secondaries, including the ter-
tials, are numbered from 1-13 (1 being the outermost).
Molt for the vestigial outermost primary (Pll) was not
recorded. A Primary Molt Score (PMS) was calculated for
each bird as the sum of the molt scores of the 10 pri-
maries in one wing, and PMS ranged from 0-50 (Ginn
and Melville 1983). When the PMS differed between
wings of the same bird, an average of the two scores was
used in analyses. Similarly, we calculated a Secondary
Molt Score (SMS, range 0-65), and a Tail Molt Score
(TMS, range 0-30) for each bird.
We determined the order in which secondary feathers
or tail feathers were molted by calculating the accumu-
lated scores for each numbered feather and ranking each
according to its accumulated score. Variations between
wings in the order of secondary molt were recorded, but
the total score was not significantly different between
wings (Mann-Whitney; W•20.•20 = 14475, P = 0.97). Molt
of tail feathers was nearly always symmetrical. Thus, we
combined values from both sides for each individual. Pri-
maries were molted sequentially, so we did not calculate
accumulated scores for them.
The extent of body molt in yearlings was categorized
for each body tract (head, mantle, coverts, breast, and
belly) on a four-point scale: 0 (no molt), I (very few new
feathers present), 2 (mixed new and old feathers), and
3 (molt finished or nearly finished).
Raggedness Scores. An index of raggedness (Haukioja
1971) was calculated for each feather tract (primaries,
secondaries, and tail), using the sum of values in each
feather of the tract. Each feather was scored with values
ranging from 0-4 according to their molt score, where 0
indicated a feather of full length (whether old or new),
4 indicates a feather at the first stage of growth (molt
score 1), 3 a feather with molt score 2, 2 a feather with
molt score 3, and 1 a feather with molt score 4. For each
individual, the sum of raggedness scores from both sides
(left and right) of each tract was used as an overall index
of raggedness.
Data Analysis. Differences in the molt scores between
males and females and age classes were analyzed with
nonparametric statistics (Mann-Whitney test). Variations
in the timing of secondary molt related to primary molt
were analyzed with linear, parametric analysis.
Since several of the skins were dated only to month
and not to day of capture, we analyzed data by month
This helped to account for latitudinal differences in phe-
nology between birds coming from different regions be-
cause breeding phenology in the Montagu's harrier var-
ies on average less than a month between southern and
northern Europe (Arroyo 1995). Initially, data for birds
from Europe (west of Ural mountains) and data for birds
that had been collected in India (presumed to breed in
the central Asian steppes) were analyzed separately. This
avoided potential differences in phenology between both
areas, since no data on timing of breeding for the Asian
populations of Montagu's harrier were available. No sig-
nificant differences in molt scores were found between
birds from both regions for equivalent months (Mann-
Whitney; W21.10 = 319.0, P = 0.47), so they were com-
bined for subsequent analyses.
RESULTS
Molt in Adults. Adult males and females started
molting on the breeding grounds in May-June,
and finished molting on the wintering grounds in
January-February (Fig. 1). Primary molt was com-
pleted in 6-8 mo. Females started molting primar-
ies before males, but both sexes finished at about
226 B. ARroYo AND J. KING VOL. 30, NO. 4
50
ß female
40 [] male
• 20
E
a. 10
5 144 20
2 5
8 4 3 5 8
4 8 4 3
e 60
o
o 50
'• 40
• 30
'- 20
o
u• 10
5 144 20
2 4 9 5
3O
2O
2 5 4 8 4 3 5 8
2
5 14 4 20
o
Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar
Figure 1. Molt phenology of flight feathers in adult Montagu's harriers. Histograms represent the mean (_SE)
primary, secondary and tail molt scores throughout the year for both males and females. Sample size (number of
individuals) is given above the histograms.
the same time (Fig. 1). The mean PMS for the
breeding months (April-July) was significantly low-
er in males than in females (Mann-Whitney; W,,4•
= 816.5, P = 0.0009), but the means were similar
in November-February (Mann-Whitney; W]],, =
185.5, P = 0.88). Accordingly, the slope of the re-
gression of PMS vs month was higher for males
(5.36) than for females (5.01).
Both males and females started molting second-
aries in August-September, and finished at the
same time that primary molt finished (Fig. 1).
Males started molting secondaries at a significantly
earlier stage of primary molt than females did
(GLM SMS = PMS + Sex; F],i• 7 = 1956.5, P =
0.0001 for PMS; F1,117 = 12.60, P = 0.001 for Sex;
Fig. 2). The pattern of secondary molt was highly
1996 MONTAGU'$ HAR•F.R MOLT 227
6O
O 50
• 40
o 10
0
Males øø•øø
o oJoO
•o oo
o
•. • rt . • . • , • .
10 20 30 40
3O
20
10
o
cma oo .9o
Males o•0
0 • 0 0
o o
i ß i , i ß i ß i
0 10 20 30 40 50
6O
o 50
-. 40
o
3o
13 20
o
o 10
0
Figure 2.
Females
'
0 10 20 30 40 50
Primary Molt Scores
Onset of secondary molt in relation to molt
of primary feathers: correlation between secondary molt
scores and primary molt scores in adult male (N = 79)
and female (N = 40) Montagu's harriers.
30 Females
o 20 s s
o
_ 10
0 -- .......
i ß i
0 10 20 30 40 50
Primary Molt Scores
Figure 3. Onset of tail molt in relation to molt of pri-
mary feathers: correlation between tail molt scores and
primary molt scores in adult male (N = 79) and female
(N = 40) Montagu's harriers.
variable among individuals in relation to the order
in which feathers were replaced. The relative order
of the accumulated molt scores of each feather (all
birds combined) was as follows: for females (N =
40): S1 (accumulated score = 180), S5/Sll (165),
S2/S13 (160), S4 (155), S12 (150), S10 (146), S9
(130), S3 (123), S6 (120), S7 (115), S8 (108); for
males (N= 79): S1 (319), S5/S12 (315), Sll (308),
S13 (307), S2 (302), S10 (295), S9 (291), S4 (272),
S3 (250), S6 (242), S7 (220), S8 (218). These re-
suits indicated that two molt foci existed at S1 and
S5, and molt at both foci started nearly simulta-
neously. Another molt center was located in the
tertials (Sl1-13), which were molted at the time,
or shortly after the outer secondaries had started
to moltß Males seemed to molt the tertials as soon
as molt in the outer secondaries had started, while
females seemed to molt them more slowly. The or-
der in which tertials were molted did not seem to
follow a fixed pattern. In general, molt was ascen-
dant from S1 and S11 (the outermost tertial), and
appeared to be centrifugal from S5. Data from D.
Forsman (in litt.) suggests that molt from S5 is as-
cendant, given that he found S4 to be one of the
last secondaries to be molted. However, we found
S4 to be one of the earlier molted secondaries in
females and it was not the last secondary to be
molted by males.
Molt of tail feathers started about June and fin-
ished about January (Fig. 1). As with secondaries,
males started molting tail feathers at a significandy
earlier stage of primary molt than did females
(GLM TMS = PMS + Sex; F1,119 = 1268.6, P =
0.0001 for PMS; F1,119 = 8.15, P = 0.005 for Sex;
Fig. 3). The order in which feathers were molted
was, as with secondaries, variable but a general pat-
tern was clear from the accumulated molt scores.
Molt of tail feathers in females usually started with
228 B. ARROYO AND J. KING VOL. 30, NO. 4
the central pair (accumulated molt score of 175),
followed by the fourth (166), sixth (161), third
(156), fifth (148) and, finally, the second (132) (N
= 40). Males had a similar molt pattern, but the
sixth pair was the first one to be replaced. The
relative order was thus T6 (accumulated score
332), T1 (328), T4 (316), T3 (314), T5 (308) and
T2 (294). As in the primaries and secondaries, tail
molt seemed to occur more rapidly in males than
in females, and the variation in values of accumu-
lated TMS among feathers was lower in males than
females. The difference between the highest and
the lowest accumulated score was 12% in males
and 30% in females which suggested that males
molted a greater number of tail feathers at any one
time than females.
Primary feathers were most ragged between No-
vember-January among females and in June
among males. Degree of raggedness in secondaries
and tail feathers was generally low throughout the
molt cycle in both sexes (Fig. 4). On average, males
had higher values of raggedness for all flight feath-
er tracts than females, but differences between the
sexes were not statistically significant (Mann-Whit-
ney; W40.80 = 2598.5, 2365.0 and 2321.5, P = 0.82,
0.65 and 0.23 for primaries, secondaries, and tail
feathers, respectively). The accumulated score of
raggedness for all tracts combined peaked for
males at values ranging from 23-32 in September-
October, while values for females peaked at 25 in
November. However, no data existed for females
for September and October.
Molt in Yearlings. We recorded no body molt in
birds collected in October or November, although
sample size was small (N = 3). A small percentage
of birds of both sexes started body molt in Decem-
ber, usually in the region of the crop, and males
also on the rump (Table 1). Central tail feathers
were also replaced in about 25% of birds of both
sexes. However, the extent of molt completed be-
fore spring migration was limited in both sexes.
The proportion of yearlings with some degree of
body molt increased throughout the spring and
summer. Although a few yearlings had not started
molting any body feather tracts by July or August,
many started but had not completed molt in most
tracts by that time. Yearling males that attempted
to breed in Madrid were at the same stage of molt
as those that did not breed (B. Arroyo unpubl.
data). Furthermore, a yearling male that bred in
1994 had molted only the central tail feathers and
part of the feathers in the region of the crop when
it arrived on the breeding grounds in Spain. Body
molt of yearlings finished in October-November.
Males retained some juvenile feathers in the ear
coverts and in the nape, which allowed aging of
second-year individuals in the hand.
There was a considerable discrepancy between
the extent of body molt in yearlings recorded dur-
ing field observations and from museum speci-
mens. Detailed plumage observations of 30 year-
lings (21 males and nine females) were made in
breeding areas in Spain. Yearling males showed
more advanced body molt than did museum spec-
imens collected at the same time of year and for
birds observed in the field, the head, breast and
belly tracts, respectively, showed evidence of molt
in 91%, 62% and 62% of individuals, compared to
43%, 29% and 14% of museum specimens (Table
1). The extent of molt recorded was also greater
for individuals observed in the field. In contrast,
yearling females observed in the field showed less
advanced body molt than museum specimens.
Only 33% of the females observed in the field
showed molting in the crop, breast, and belly, com-
pared to over 63% of the museum specimens (Ta-
ble 1). This discrepancy might be an artifact of the
relatively small number of specimens of yearlings,
but it may well be a consequence of the relative
visibility of newly-molted, grey plumage in yearling
males, leading to overestimation of the extent of
molt when recorded in the field. In the latter case,
the similarity between old and new plumage in fe-
males would lead to an underestimation of the ex-
tent of body molt in that sex. Furthermore, year-
ling males showing little or no molt may have been
misidentified as females in the field, or more likely,
left unsexed due to apparently conflicting charac-
ters such as small size but no visible male plumage
features.
Primary molt in yearlings apparently started at
the same time as that of adults (Fig. 5) and molt
scores were similar between both age groups in
April-July (Mann-Whitney; W90,12 = 194.5, P = 0.90
for females; W4•.•0 = 284.0, P = 0.64 for males).
The completion of primary molt in October-Feb-
ruary also appeared to be similar for yearlings and
adults, however sample sizes were very small for the
yearling group (Mann-Whitney; W22,4 = 57.5, P =
0.83 for males; insufficient data for females to al-
low statistical analysis).
Molt of secondary and tail feathers followed the
same pattern, and occurred at the same time in
relation to primary molt, as in adults. Juvenile
DECEMBER 1996 MONTAGU'S HARRIER MOLT 229
20-
Primaries
4
2
2 2
ß females
[] males
2 3
2O
o
o
Secondaries
5 14 4 20 2 4
5 8
4
9 5 0 0 0 1 I 4 5 8
20 Tail
2 1
lO
5 4 8 8
5 14 4 9 0 0 0 I•..•==T• 4 3 5,_•__,
Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar
Figure 4. Degree of raggedness in flight feather tracts throughout the year in adult Montagu's harriers of both
sexes. Histograms represent the mean (-SE) raggedness scores for primaries, secondaries and tail feathers. Sample
s•ze (number of individuals) is given above the histograms.
feathers were replaced by feathers similar to those
of adults, only slightly darker. Thus, after the first
complete molt, yearlings were indistinguishable
from older birds in the field as confirmed by ob-
servations of dark-looking plumage in known-age
wing-tagged individuals ->3 years old.
Molt in Second Year Males. Fourteen males in
adult plumage could be identified as second-yr
males by the presence of a few unmolted, juvenile
feathers on the nape or ear coverts. Second-yr
males started molt at the same time as older males,
and from May-July the scores for the two age-class-
es were similar (Mann-Whitney; W•4,9 = 231.0, P --
0.13). However, in November-February, second-yr
males had higher PMS than older males, and the
difference approached significance (Mann-Whit-
ney; W16,4 ---• 60.5, P = 0.08). Similarly, second-yr
males had higher values of SMS than older males
230 B. ARROYO AND J. KING VOL. 30, NO. 4
Table 1. Percentage of yearling specimens of Montagu's harriers in which molted feathers were present in different
feather tracts. Figures in brackets show the mean score of the individuals in molt (1 [only a few feathers]-3 [molt
complete]). N = number of individuals; LC, MC, GC = lesser, middle, and greater coverts, respectively; CTF =
central tail feathers; OTF = other tail feathers.
DATE N HEAD CROP BREAST BELLY LC/MC GC MANTLE RUMP CTF OTF
Males
Dec-Jan 9 0 33.3 22.2 0 11.1 0 0 33.3 11.1 0
(3.0) (2.0) (2.0) (3.0) (2.0)
Feb-Mar 3 33.3 66.6 0 0 0 0 0 66.6 0 0
(1.0) (1.0) (3.0)
Apr-May 7 42.8 85.7 28.6 14.3 42.8 14.3 28.6 57.1 57.1 14.3
(1.3) (1.8) (1.5) (2.0) (2.0) (1.0) (1.5) (2.0) (3.0) (2.0)
Jun-Jul 3 66.6 100 66.6 33.3 0 0 0 66.6 100 66.6
(1.0) (2.0) (2.0) (1.0) (1.5) (2.0) (2.0)
Aug 2 50.0 50.0 100 100 100 100 50.0 100 50.0 50.0
(1.0) (3.0) (2.5) (2.0) (1.5) (2.5) (1.0) (3.0) (3.0) (2.0)
Females
Dec-Jan 6 0 16.7 16.7 16.7 0 0 0 0 50.0 0
(2.0) (2.0) (2.0) (2.7)
Feb-Mar 5 0 40.0 40.0 20.0 0 0 0 20.0 20.0 20.0
(1.0) (1.0) (1.0) (3.0) (3.0) (2.0)
Apr-May 8 37.5 87.5 62.5 62.5 25.0 0 0 25.0 37.5 0
(2.0) (1.8) (1.5) (2.2) (1.5) (1.0) (3.0)
Jun-Jul 3 66.6 100 66.6 66.6 66.6 33.3 0 66.6 100 100
(1.5) (2.6) (2.5) (2.5) (2.5) (3.O) (1.5) (2.0) (2.0)
during same period, although the difference was
not significant (Mann-Whitney; W•s,4 = 55.0, P =
0.14), perhaps due to small sample sizes.
DISCUSSION
Molt started in the breeding season (June-July)
and finished during the winter months approxi-
mately 6-8 mo later, indicating that the molt pe-
riod in Montagu's harrier is long compared to that
of nonmigratory raptors of comparable body size
such as northern goshawks (Accipiter gentilis; Read-
ing 1990), sparrowhawks (Accipiter nisus; Newton
and Marquiss 1982), and little banded goshawks
(Accipiter brevipes; Schmitt et al. 1981). We could
50'
ß females
40' [] males
= 30
o
• 20
E
'= 10
I 2
2
7
1 3 4 0 0 0 0 0 0 0 0
o
Apr May Jun Jul A• Sep Oct Nov Dec Jan Veb Mar
Figure 5. Molt phenology of primary feathers in yearling Montagu's harriers. Histograms represent the mean
(_ SE) primary molt scores throughout the year for both males and females. Sample size (number of individuals)
is given above the histograms. Secondaries and tail feathers, as in adults, are molted in the interval when primaries
are molted.
DECEMBER 1996 MONTAGU'S HARRIER MOLT 231
not confirm that birds suspended molt during the
migration, as no birds were collected on the mi-
gratory route. However, molt scores of birds col-
lected in August-October in either breeding or
wintering areas together with high molt scores of
the birds collected in November on the wintering
grounds, suggested that at least some birds contin-
ued to molt while migrating. The duration of the
autumn migration is unknown, but may be in ex-
cess of 1 mo given the average dates of departure
from the breeding grounds (Studinka 1941, Petre-
ment 1968, Perez Chiscano and Fernandez Cruz
1971, Kjellen 1992, Martelli and Parodi 1992, Ar-
royo 1995), and dates of arrival in wintering areas
(Morel and Roux 1966). Migratory flight of harri-
ers seems to be slow and generally at relatively low
altitudes. They combine flapping and gliding and
hunting along the way (Brown 1976, Ali and Ripley
1978). This mode of migration may allow harriers
to continue molting slowly while migrating as they
are not soaring birds, for which gaps in the wings
would represent higher energetic costs. Piechocki
(1955) observed molt in a single captive pallid har-
rier (Circus macrourus). Each tail feather took 45 d
to grow completely. Presumably, the primaries
would take longer to grow especially from P5 on-
wards. If single primaries are not shed until growth
of the previous one is nearly finished, harriers may
keep molting at a slow rate during the migration
instead of suspending molt.
As in goshawks and sparrowhawks (Newton and
Marquiss 1982, Reading 1990), molt of primaries
in Montagu's harrier was spread throughout the
entire molt cycle. Secondaries were molted later in
the season, but finished at approximately the same
time as the primaries. In raptors, molt of second-
aries and especially of tail feathers, occurs more
quickly than that of primaries (Newton and Mar-
quiss 1985, Underhill 1986, Schmitt et al. 1987). In
the Montagu's harrier, molt of the secondaries ei-
ther did not start, or was not apparently advanced
before autumn migration. Secondaries provide
much of the lift required for flight (Newton and
Marquiss 1982), so it may be especially important
to minimize gaps in these feathers for long-dis-
tance migration. In accordance with this hypothe-
sis, raggedness scores in the secondaries were al-
ways low in comparison with those of primaries.
Males started molting later than females. A sim-
ilar temporal difference in the onset of molt be-
tween sexes has also been documented in sparrow-
hawks (Newton and Marquiss 1982) and northern
harriers (Circus cyaneus hudsonius; Schmutz and
Schmutz 1975). Breeding birds must divide their
energy between two energetically costly tasks:
breeding and molting. In Ural owls (Strix uralensis),
breeding delays molt and the number of molted
feathers is inversely related to energy expended
during the previous breeding season (Pietiainen et
al. 1984). Therefore, in species in which males do
most of the hunting in the breeding season, a sex-
ual dimorphism of molt initiation is expected. In
Montagu's harrier, females contributed less than
15% to the feeding of nestlings and fledglings (Ar-
royo 1995). Females can start molting during in-
cubation, when their energy expenditure is less
than that of hunting males. The onset of molt in
female sparrowhawks was related to the date they
started laying (Newton and Marquiss 1982), but
such a relationship was not found in northern har-
riers (Schmutz and Schmutz 1975) or Swainson's
( Buteo swainsoni) or ferruginous ( B. regalis) hawks
(Schmutz 1992). Most female Montagu's harriers
observed in Madrid appeared to have started molt
soon after incubation began (B. Arroyo unpubl.
data), but it is not known whether the timing of
molt was correlated with timing of egg laying.
As in the northern harriers (Schmutz and
Schmutz 1975), male Montagu's harriers appar-
ently molted at a faster rate than females. Female
feathers are longer (Nieboer 1973), and may take
slightly more time to reach their full length. How-
ever, in sparrowhawks in which sexual dimorphism
is much greater than in Montagu's harriers, differ-
ence between the sexes in the duration of molt is
related to the interval between shedding feathers,
not the time that each individual feather takes to
grow to its full extent (Newton and Marquiss
1982).
Both sexes differed slightly in the order which
secondary and tail feathers were molted. Females
molted secondaries 2 and 4 before finishing the
tertials, whereas molt of the tertials proceeded at
a faster rate in males. Additionally, males molted
the outermost tail feathers before any other. The
adaptive reasons (if any) for these different strat-
egies are unclear, and the apparent pattern might
be an artifact of sample size used in our study.
Yearlings do not usually have the same energetic
costs of adults, and their plumage is usually of
poorer quality. Thus, it would be expected that
they start replacing their flight feathers earlier than
adults. This has been found to be true of yearling
sparrowhawks (Newton and Marquiss 1982), cap-
232 B. ARROYO AND J. KiNG VOL. 30, No. 4
tive goshawks (Reading 1990), and pallid harriers
(Circus macrourus; Piechocki 1955). In this study,
yearlings did not appear to start molt significantly
earlier than adults. This again may have been due
to sample size limitations; however, younger birds
are less experienced hunters than adults, so they
may be under higher nutritional stress, especially
individuals that have undergone spring migration.
Some yearlings summer in Africa and apparently
they replace remiges faster than birds returning to
the breeding grounds (D. Forsman, in litt.). In this
study, the highest PMS among yearlings early in the
cycle were shown by females that bred (shot while
incubating), possibly because they were fed by
males, and were in better condition than other
yearlings (of either sex) that had to hunt for them-
selves. On the other hand, yearlings seemed to
complete molt before adults although the differ-
ences were not significant. Second-yr males, which
are probably nonbreeders (given that most males
do not start breeding until the third year; Cramp
and Simmons 1980), appeared to finish molt be-
fore older males. This suggests that nonbreeding
birds molted at a faster rate. Alternatively, different
age groups might have different migration strate-
gies, which in turn might influence molt if year-
lings migrate at a slower rate. If young birds make
more stopovers to feed, they might be able sustain
a higher rate of molt in flight feathers as has been
shown in steppe buzzards (Buteo buteo vulpinus;
Gorney and Yom-Tov 1994).
ACKNOWLEDGMENTS
We are very grateful to Peter Colston (NHM, Tring),
Josefina Barreiro (MNCN, Madrid) and the ORSTOM
Station (S•n•gal) for access to their collections, and to
Dick Forsman, Josef Schmutz, Bruce MacWhirter and Ian
Newton for valuable comments on the manuscript.
LITERATURE CITED
ALI, S. AND S.D. PdPLE¾. 1978. Handbook of the birds of
India and Pakistan. Vol. 1. Oxford University Press,
Oxford, UtC
AP•oYo, B.E. 1995. Breeding ecology and nest disper-
sion in the Montagu's harrier Circus pygargus in cen-
tral Spain. Ph.D. dissertation. Oxibrd University, UK.
BORTOLOTTI, G. ^ND V. HONE•MAN. 1985. Flight feather
molt of breeding bald eagles in Saskatchewan. InJ.M.
Gerrard and T.N. Ingram [EDS.], The bald eagle in
Canada. Proc. of Bald Eagle days, 1983. White Horse
Publishing, Winnipeg, Manitoba, Canada.
BROWN, L.H. 1976. British birds of prey. Collins, Lon-
don, UtC
CRAMP, S. AND K.E.L. SIMMONS lEDS.]. 1980. The birds
of the western Palearctic. Vol. 2. Oxford University
Press, Oxford, UtC
EDELSTAM, C. 1984. Patterns of moult in large birds of
prey. Ann. Zool. Fenn. 21:271-276.
GINN, H.B. AND D.S. MELWLLE. 1983. Moult in birds.
B.T.O. Guide 19. British Trust for Ornithology, Tring,
UI•
GORNEY, E. AND Y. YoM-Tov. 1994. Fat, hydration con-
dition and moult of steppe buzzards Buteo buteo vul-
pinus on spring migration. Ibis 136:185-192.
HAUK•OJ^, E. 1971. Processing moult card data with ref-
erence to the chaffinch Fringilla coelebs. Ornis Fenn. 48:
25-32.
HOUSTON, D.C. 1975. The moult of the white-backed
and Rfippell's griffon vultures Gyps africanus and G
rueppellii. Ibis 117:474-488.
KJELLEN, N. 1992. Differential timing in autumn migra-
tion between sex and age groups in raptors at Fal-
sterbo, Sweden. Ornis Scand. 23:420-434.
MARTELLI, D. AND R. PARODI. 1992. Albanella minore C•r-
cus pygargus. Pages 541-550 in P. Bichetti, P. De Fran-
ceschi and N. Baccetti [EDS.]. Fauna d'Italia. Ucelli I.
Calderini, Milan, Italy.
MILLER, A.H. 1941. The significance of molt centers
among the secondary remiges in the Falconiformes.
Condor 43:113-115.
MOREL, G. AND E Roux. 1966. Les migrateurs pal•arc-
tiques au S•n•gal I--les non-passereaux. Terre Vie 20.
19-72.
NEWTON, I. AND M. MA•QUISS. 1982. Moult in the spar-
rowhawk. Ardea 70:163-172.
NIEBOER, E. 1973. Geographical and ecological differ-
entiation in the genus Circus. Ph.D. dissertation. Free
University, Amsterdam, Netherlands.
PEREZ CHISCANO, J.L. AND M. FERNANDEZ CRUZ. 1971. So-
bre Grus grus y Circus pygargus en Extremadura. Ardeo-
la Spec. Vol.
PETREMENT, B. 1968. La nidification du busard cendr6
(Circus pygargus) en Lorraine Belge en 1967. Aves 4:
80-87.
PIECHOCKI, R. 1955. l)ber Verhalten, Mauser und timfar-
bung einer gekfifigten Steppenweihe (Circus macrou-
rus). J. Ornithol. 96:327-336.
PIETIANEN, H., P. SAUROLA AND H. KOLUNEN. 1984. The
reproductive constraints on moult in the Ural owl
Strix uralensis. Ann. Zool. Fenn. 21:277-281.
READINC, C.J. 1990. Molt pattern and duration in a fe-
male northern goshawk (Accipiter gentilis). J. Raptor
Res. 24:91-97.
SCHMITT, M.B., S. BAUR AND F. VON MALTITZ. 1981. Men-
sural data, moult and abundance of the little banded
goshawk in the Transvaal. Ostrich 53:74-78.
--, AND --. 1987. Observations on the
,
jackal buzzard in the Karoo. Ostrich 58:97-102.
SCHMUTZ, J.}C 1992. Molt of flight feathers in ferrugi-
nous and Swainson's hawks. J. Raptor Res. 26:124-135.
--AND S.M. SCHMUTZ. 1975. Primary molt in Circus
DECEMBER 1996 MONTAGU'S HARRIER MOLT 233
cyaneus in relation to nest brood events. Auk 92:105-
110.
STV,•SEMANN, E. •tND V. STV,•SEMANN. 1966. Die Mauser
der Vogel. J. Ornithol. 107:1-447.
STUD•NKA, L. 1941. The habits and plumages of Monta-
gu's harrier. Aquila 46-49:247-268.
UNDERHILL, L.G. 1986. A graphical method to deter-
mine the ordering of moult, illustrated with data for
the black-shouldered kite Elanus caeruleus. Bird Study
33:140-143.
Received 29 November 1995; accepted 22 August 1996
