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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 123. No. 4. December 2011 
larger than females in all measurements consid¬ 
ered. Measurements most useful in differentiating 
adult males and females were body mass, total 
length, occipital width, bill length, and wing 
chord. These measurements may be used to 
decrease handling time in future field work. 
Generally, male hummingbirds tend to be larger 
than females (Grantsau 1988. Johnsgard 1997), 
and it is not surprising that Hyacinth Visorbearers 
were consistent with this pattern. The measure¬ 
ments of bill length, wing chord, and tail length 
documented by Abreu (2006), the only morpho¬ 
metric variables for which means and ranges were 
available lor males and females, are also consis¬ 
tent with our findings (i.e., that males are larger 
than females). 
Abreu (2006) noted small differences in means 
and ranges for certain variables, including body 
mass, wing chord, and tail and bill length. The 
ranges of Abreu*s (2006) measurements were 
narrower than those in our study. It is likely these 
differences are due to the greater number of 
individuals we measured. The total length of males 
was the only measurement taken by Abreu (2006) 
that had a higher mean (98.2 mm) and greater range 
(81-108 mm). The number of individuals (n = 14) 
measured by Abreu (2006) was small and possibly 
not viable for comparisons. These individuals were 
also captured at different locations along the 
Cadeia do Espinha^o, suggesting this particular 
measurement may vary to a greater extent than 
other morphometric measurements between differ¬ 
ent populations of Hyacinth Visorbearer. 
The feather coloration pattern of juvenile male 
Hyacinth Visorbearers observed in our study is 
consistent with the description of blue on the neck 
noted by Schuchmann (1999) and Abreu (2006) 
However, previous studies have not fully de¬ 
scribed the plumage coloration and patterns of 
juvenile male and female Hyacinth Visorbearers 
Our study suggests it is possible to accurately 
assign gender of the majority of juvenile Hyacinth 
Visorbearers based mainly on coloration of the 
side of the neck and the tract of feathers that 
circles the visor. It is common to find different 
plumage patterns between juvenile male and 
female hummingbirds that exhibit strong sexual 
(Newe11 ct al - 2007, Juina et al. 
for nn , l ! may ° ffei ' a sim P ,e and im P™ant tool 
There is some indication of a greater concentra¬ 
tion of reproductive effort during the dry season, 
when more juveniles and active nests were 
recorded. However, captured fledged young in 
January. February, and March support a breeding 
period lor the Hyacinth Visorbearer of throughoui 
the year. Further evidence is necessary to confirm 
this hypothesis. The reproductive period of tropical 
hummingbirds is usually synchronized with peaks 
in flowering of particular plant species during the 
dry or rainy season (Skutch 1950. Stiles 19S0. 
Schondube et al. 2003), which seems to be directly 
associated with preference of certain hummingbird 
species for specific blooming plants. Some species 
ot hummingbirds, however, are known to breed 
throughout the year ( Johnsgard 1997). 
The abundance of flowers in AP that Hyacinth 
Visorbearer are known to visit was constant 
throughout the year; the highest density of non- 
omitophilous flowers was registered at the end of 
the rainy season and early dry season (Rodrigues 
2011), which coincides with the increase of young 
of this species. The consistent availability of 
preferred resources may favor the capacity of this 
hummingbird to reproduce throughout the year. 
However, there is nearly constant rainfall in the 
region from November to February. There are 
certain periods, particularly during December and 
January, when there is constant rainfall for as 
many as 10 consecutive days or more (L. C. 
Rodrigues, pers. obs.). Rainfall can have a direct 
influence on concentration of nectar (Aizen 2003), 
which consequently can cause the birds to avoid 
expending energy on acquiring highly diluted 
nectar (Rocca-de-Andrade 2006), which has a 
much lower energetic value. Moreover, nests of 
Hyacinth Visorbearers were recorded in small 
shrubs and exposed to direct sunlight and rain. 
Thus, it may be more advantageous for Hyacinth 
Visorbearers to reproduce during the dry season 
when risk of damage to nests, as well as nectar 
dilution, is less and the energetic value of 
available resources is likely to be much higher 
Further work on this species should examine 
whether or not the Hyacinth Visorbearer has one 
or more reproductive periods per year and if the 
parapatric species, Hooded Visorbearer (Augastes 
lumachella), exhibits similar juvenile plumage 
patterns. Ultimately, more comprehensive and 
long-term life history studies of this and other 
possible threatened and endangered species in 
southeastern Brazil and elsewhere are needed for 
effective conservation planning. 
