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					58                                                                                                      2003

Biometrics
                     The Grey Sunbird in the Eastern Cape
                                                A.J. Tree
          “Chirawanoo”, Box 211, Bathurst, 6166; tony.tree@xsinet.co.za

Occupying suitable evergreen dune and valley             loads; the occurrence of birds at these sources
forest and bush along the narrow coastal belt,           may vary, dependent on this latter factor and the
the Grey Sunbird Cyanomitra veroxii is found             presence of any birds in the area. Evidence has
in a habitat in which few bird ringers operate.          been accumulating over the last eight years that
Consequently, this is a species that is handled in       this species is migratory to some degree in the
very small numbers and of which little is known.         western part of the birds range in the Eastern
It is an enigmatic species with puzzling habits and      Cape but the extent of these movements remains
as Skead (1967) says “Where one day a forest             a mystery. Based on ringing and intensive field
will be alive with the song of this bird, the next       observations, birds tend to leave the area from
and subsequent days will be silent at the same           March and return in late July or August with oc-
time of day and at the same places”. The choice          casional over-wintering.
of habitat is such that if this bird remains silent it
is very difficult to locate and it is normally only      Ageing and sexing
to visit suitable nearby nectar sources that it will     This is a difficult bird to sex as plumage dimor-
venture from its chosen haven. Further, the over-        phism is slight and there is a degree of overlap
all numbers in any given year vary enormously            in measurements. The red pectoral tuft of the
and densities are rarely high.                           male is generally larger than that of the female
     My two-acre garden is situated on the top of        and tends to have a couple of pronounced
a cleared ridge on the extreme western outskirts         yellow feathers which are missing or short and
of Bathurst and borders onto a well-forested             subdued in the female. Ageing is easy as the ju-
kloof in the front of the property with extensive,       venile and immature have a bright orange gape
evergreen valley bushveld some 200 m to the              (clearly visible in the field), this becoming increas-
west. Despite this proximity to suitable bush it         ingly reduced during the second half of the year.
is only in recent years, as the trees, bushes and        Young birds also have reduced gloss on the
aloes in my garden mature, that the Grey Sunbird         upperparts and start to assume the pectoral tuft
has become a fairly regular garden visitor. To           during and after their first moult from juvenile
give an indication of this steady increase and           plumage.
annual variation only four unringed birds were               Measurements may be used to sex the
caught from 1991 to 1996, 15 in 1998 (first              majority of adults in the Eastern Cape population
major flowering of the Schotia afra), eight in           (Table 1), as the figures given in Robert’s
1999, three in 2000, eight in 2001 and 16 in             (Maclean 1993) appear to apply to smaller birds
2002. These birds, although heard singing from           in KwaZulu-Natal. Few juvenile/immature birds
the tops of trees, only come down to net level           may be adequately or safely sexed in this way.
with the flowering of the favoured Karoo boer-
boen Schotia afra, Cape honeysuckle Teco-                Biometrics
maria capense and the exotic Weeping                     The important measurements to use are those of
bottlebrush Callistemon species. Unfortunately           wing (maximum chord), tail (underneath) and
these species flower erratically and with vary-          mass (Table 1). The tail measurement may be
ing intensity and, I suspect, with variable nectar       the most diagnostic and the figures shown in

Afring News (2003) 32: 58-59
Afring News 32(2)             Tree: Grey Sunbird in the Eastern Cape                                     59

Table 1. Adult Grey Sunbird biometrics for the Eastern Cape

                 Age/Sex             Sample size     Range                Mean         S.D.

Wing             Ad M/F                 38           59.0–69.0              64.0        2.8
                 Ad M *                              65.5–69.0
                 Ad F *                              59.0–64.0
Tail             Ad M/F                 38           44.0–57.5              51.0        4.0
                 Ad M *                              54.0–57.5
                 Ad F *                              44.0–50.0
Culmen           All ages               55           27.0–31.0              29.1        1.4
Tarsus           All ages               55           17.0–19.0              18.1        0.6
Mass             Ad M/F                 38           10.6–15.1              12.7        1.1
                 Ad M *                              12.0–15.1
                 Ad F *                              10.6–13.1

* This study suggests that Eastern Cape birds with wings of 65.5 mm or longer and tails of 54 mm and longer
are males and those with wings of 64 mm or shorter and tails of 50 mm or shorter are females.


Robert’s (loc. cit.) give this impression but the      primary moult with last two or three feathers still
sample size there is too small. Data collected         growing, secondaries active, body complete and
from this study suggest that Eastern Cape birds        tail just or almost complete. The bird caught at
with wings of 65.5 mm or longer and tails of           the beginning of April was completing P9, re-
54 mm and longer are males and those with              mainder (P1–8 and P10) new; only the two in-
wings of 64 mm or shorter and tails of 50 mm           ner secondaries were late active and tail new;
or shorter are females. In this way 84% of adult       body moult was still mid-active. The immatures
birds were sexed. Mass may not be totally reli-        had P1–3 active or new, the latter also had P4–
able as an ovid female may well weigh more than        5 active, secondaries had only started moult in
many males, and may vary as to time of day and         the more advanced birds while tertials were ac-
season. Individuals may show up to a 20%               tive in all birds; tail had inner four or six feathers
weight variation. However, outside of the breed-       active in the more advanced birds while all birds
ing season it may still be a useful additional aid     had variable activity in body moult. More data
for sexing. Culmen and tarsal measurements are         is needed but it is likely that moult may take 6–
similar in both sexes and all ages. The range of       8 weeks to complete.
wing, tail and mass measurements are given (see
Table 1) for birds determined to be males or           Recaptures
females but must not be treated as the absolute        Few birds have been recaptured and of seven
limits for each sex. Wing and tail are not shown       in my records five were within two weeks of initial
for juvenile/immature as they are shorter than in      capture. An adult male ringed in August 1996
adults until the first moult is complete.              was recaught in October 2000 and February
                                                       2001 and was likely a local breeding bird. A
Moult                                                  juvenile caught in February 2001 was recap-
I have caught eight birds during active moult, of      tured later in August.
which four were adult, mid-February to begin-
ning April and the remainder immatures in mid-         References
February. The February adult was at the early          Maclean G.L. 1993. Roberts’ Birds of Southern Af-
stage of growth in the first three primaries (P1–         rica. Trustees of the John Voelcker Bird Book
3), secondaries old, tertials replacing, tail just        Fund, Cape Town.
dropped central two feathers and body active;          Skead C.J. 1967. Sunbirds of Southern Africa.
                                                          South African Bird Book Fund, Cape Town.
the two mid-March adults were in late stage

				
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