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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 124. No. 4. December 2012 
relatively low canopy height influenced by 
hurricanes; recent hurricanes that have directly 
impacted Cozumel include Gilbert (1988). Rox¬ 
anne (1995). Emily (2005), and Wilma (2005). 
Our study site was a set of paths leading from an 
area known locally as Pueblo Fantasma (20 26' 
54" N. 86 57' 32" W), an isolated and mostly 
abandoned residential development (Howell 
1999:311) ~6 km south of San Miguel, the 
island’s primary town. This area was easily 
accessible with vegetation representative of Co¬ 
zumel’s interior forests. 
Nes1 Searching and Monitoring .—JBL discov¬ 
ered three Cozumel Vireo nests while systemat¬ 
ically searching for catbird nests. We checked 
nest contents every' 1-3 days (although one nest- 
check interval lasted 8 days). 
Measurements .—We measured nest height from 
nest bottom and top. tree height, nest circumfer¬ 
ence, distance to stem, and angled distance to 
stem using a tape measure. We used calipers to 
measure nest and egg dimensions. 
OBSERVATIONS 
Nesting Cycle and Nesting Phenology.— JBL 
tscovered the first Cozumel Vireo nest (# 1 ) on 1 
June 2009 (Fig, I) containing two eggs at 1136 
and .830 hrs (COT). The nest contained*™ eggs 
on 2 June 2009 at 1114 hrs. The last dav we 
observed the nest with eggs was 15 June 2009 at 
chVu • , and WC ° bserved tWo recently-hatched 
chicks and one un-hatched egg in the nest on 17 
June 2009 a, ,854 hrs. .negation latd ! 4 dall 
it ue assume incubation began with clutch 
comp ei,on (2 Jun 2009) and the chicks hatched 
i June 2009, die day between the last 
~o f "T f 8gS and ,he r,m “‘“crvation 
£*£7 ’’ 6 ” ^ °" ^ -d 0731 te 
^7 June 20 ° 9 and |04() hjs on 28 ‘ JJ- ™ 
A second Cozumel Vireo nesi ’ . 
one recently hatched chick and „n . / cont£ nned 
discovery (17 Jun 2009 at 0955° S° n d , ate ° f 
chicks and no eggs at the next n . ,u1f lvv ° 
2009 a, ,835 hrs). Thh <l9 ' Ju ” 
CWCks 29 2009 and was e,,Xn 30 C 
2009. We infer successful Hedging of at least one 
chick from this nest based on the presence of an 
adult Cozumel Vireo persistently scold-calling in 
the immediate vicinity on 30 June and I Julv 
2009. These observations suggest the nestling 
stage lasted ~12 days if we assume 1 1) the eggs 
hatched on the day of nest discovery and (2) at 
least one chick successfully fledged. The approx¬ 
imate total length of the nesting cycle, including 
egg-laying, incubation, and nestling stages, is 
~27-28 days, combining data from both nests. 
A third nest (#3). discovered with two eggs at 
1014 hrs on 20 June 2009, yielded incomplete 
data because of abandonment. We observed a bird 
incubating at 1712 hrs on 20 June 2009. at 0952 
hrs on 21 June 2009, and at 0936 hrs on 23 June 
2009. Two eggs were present on 28 June 2009. 
but a leaf covered both at 0717 hrs on 29 June 
2009. The leaf remained on 2 July 2009. which 
suggests the parents abandoned this nest between 
23 June 2009 and 29 June 2009. 
JBI. observed an adult V. bairdi provisioning a 
well-developed fledgling (i.e., flying with the 
adult) at 1607 hrs on 22 June 2009 in an area 
separate from the three vireo nests. This observa¬ 
tion suggests at least one successful nest was 
initiated before the end of May, if we assume a 
nesting cycle of 27-28 days. Our combined 
observations indicate that Cozumel Vireos breed 
Irom late May through June. If nest #3 had not 
been abandoned, it likely would have been active 
at least into the beginning of July, which would 
extend the known breeding period. 
Nest Description .—Each of the three nests hung 
between two horizontal forks of a lateral branch 
w ith the rim woven about the supporting branches 
( Fig. I A). Each nest’s outer cup comprised plant 
fibers interwoven with spider silk and well- 
decomposed leaves, and adorned with bits ol 
lichen, bark, and thin, black rootlets (Fig. 1A). 
The nest lining consisted of an open network of 
ihin, dried grass fragments (Fig. IB). Nest 
dimensions (Tahle 1) varied because of differenc¬ 
es associated with position of the nest rim in 
relation to the supporting branches. 
All three nests were placed low (< 2 m) 
in relatively short trees (< 2.7 m). at varied 
distances from the main stem (Table 1). Floral 
parts necessary for definitive identification Were 
absent, but the plant supporting one nest was 
identified as a member of the family Myrtaceae 
(possibly Eugenia sp.; Israel Acosta-Rosado, pers. 
«'min.), 
