Blake and Loiselle • VARIATION IN GLYPHORYNCHUS ABUNDANCE 
443 
Capture rates also vary substantially in Central 
America. Glyphorynchus was infrequently cap¬ 
tured in Kan’s (1990) long-term studies along 
Pipeline Road. Panama, and none was captured in 
Schemske and Brokaw's (1981) study in the same 
area. In contrast, Glyhphorynchus was more 
common in Comarca de Kuna Yala. Panama with 
capture rates varying from 2.4 (50 m elevation) 
to 0.9 (850 m) per 100 mn/hr (Blake 1989). 
Glyphorynchus also was one of the most fre¬ 
quently captured species in Costa Rica (e.g.. 
Blake and Loiselle 1991, 2000, 2001), where 
capture rates ranged from 0.7/100 mn/hr in second 
growth to —2.7 in old-growth forest at 50 m and 
4.7 in forest at 500 m. 
Observation data indicate even greater variation 
in abundance among sites than capture data. 
Densities of Glyphorynchus were low in central 
Panama along Pipeline Road (8/100 ha; Robinson 
et al. 2000), in agreement with the very low 
capture rates, and in Manu, Peru, where densities 
were approximately the same or lower (2.75 pairs/ 
100 ha; Terborgh el al. 1990). Capture rates were 
not available for the Peru site but Glyphorynchus 
was ranked second in numbers of captures (Karr 
et al. 1990). Densities were somewhat higher 
(16.5 pairs/100 ha) in a plot in the forest frag¬ 
ments project north of Manaus (Johnson et al. 
2011) and ranked about fourth in number of 
captures. Similarly. Thiol lay (1994) reported 
densities from 28 to 36 pairs/100 ha in French 
Guiana with Glyphorynchus the most frequently 
captured species. English (1998). working close to 
our study site, estimated Glyphorynchus densities 
at — I/ha. the highest recorded by any study, and 
in agreement with our capture rates which are the 
highest reported. 
Overall density of entire bird communities does 
not. however, appear related to Glyphorynchus 
density or capture rate. The Panama site, for 
example, has the highest total density of birds 
(Robinson et al. 2000) but one of the lowest 
densities and capture rates for Glyphorynchus. 
Total density at the Manaus site (Johnson ct al. 
2011) is less than in Peru (Terborgh et al. 1990) 
but density and capture rate of Glyphorynchus 
were higher in the former site, although Glypho¬ 
rynchus ranked slightly higher among captures in 
the latter site (4 vs. 2). 
An evaluation of factors that might cause 
geographic variation in abundance is beyond Ihe 
scope of this paper. Habitat, foraging sites, 
resource abundance, abundance of ecologically 
similar species (Poletto et al. 2004), and environ¬ 
mental conditions all might influence the number 
of individuals in a given region, but few data are 
available to allow examination of their influence. 
Rainfall and strength of the dry season may have 
an influence on Glyphorynchus abundance. The 
three sites with the highest abundances (whether 
by capture rate or territory mapping) were Costa 
Rica, French Guiana, and Ecuador (2 sites). All of 
these sites have rainfall of at least —3,000 mm per 
year and no strong dry season. The other sites in 
Venezuela. Brazil. Peru, and Panama have rainfall 
of — 1.700 to —2.600 mm per year and have more 
pronounced dry seasons; Glyphorynchus abun¬ 
dance was lower in these sites. Glyphorynchus 
often forages in moss growing on tree trunks 
(English 1998) and it is possible that lower 
rainfall and more pronounced dry seasons may 
limit this foraging option. 
Glyphorynchus is one of the most abundant 
birds in the understory of wet tropical forests of 
Central and South America. Its abundance varies 
both spatially (at both local and geographic scales 
of analysis) and temporally (i.e„ across years). 
Spatial variation likely is linked to habitat 
preferences at a local scale and, perhaps, with 
rainfall or other environmental factors at larger 
geographic scales. Future studies that examine 
movements in relation to foraging behavior or 
studies that examine reproductive success and 
foraging behavior in different geographic regions 
may lend further insight into the population 
dynamics of this common neotropical species. 
Similar studies on additional species may reveal 
whether patterns shown by Glyphorynchus are 
unique or shared by other species. 
ACKNOWLEDGMENTS 
We are grateful to the individuals who helped establish 
the 100-ha study plots or assisted in collecting field data: 
Javier Andy. Renata Duraes, Jeanne Fair, Alvaro Garcia. 
Jose Hidalgo, Kimberly Holbrook. Franklin Narvaez, 
Jcndry Narvaez. T B. Ryder. J.-C. Rodriguez, Tina 
Sommers, and W. P. Tori. We also thank the staff of the 
Tiputini Biodiversity Station, especially Jaime Guerra. 
Diego Mosquera, Consuelo de Romo. David Romo, Kelly 
Swing, and all others who have made our visits to the site so 
rewarding. The National Science Foundation (IBN 
02.15141). National Geographic Society 17113-01), Fulb- 
right U.S Scholars Program, University of Missouri-St. 
Louis, and University of Florida provided fundinc. Work at 
Tiputini Biodiversity Station was conducted in accordance 
wtlh research permit # 13-tC-FAU-DFN (and renewals), 
Ministeno del Ambiente. Distrito ForesfaJ Napo. Tena 
Ecuador. 
