Background: (Oxidative stress of birds in natural gaps and understory sites in
the Amazon region). Studies that provide information about the distribution of
birds in different phases of forest mosaic are essential for understanding the
maintenance of biodiversity, since natural gaps play a central role on the
structure and dynamics of tropical forest. Objectives: (a) to determine and
compare the abundance and richness of frugivorous birds between the natural
gap and understory habitats; (b) verify and associate the abundance of
frugivorous birds with the availability of fruits in both areas; (c) to investigate the
echophysiological interactions between the oxidative stress and the distribution
of specimens of Dixiphia pipra and Willisornis poecilinotus, to determine which
factors account for the variance of biomarkers of oxidative stress in these
species. Methods: This study was carried out from November 2010 to October
2011 in terra firme forest sites at the National Forest of Caxiuanã, Melgaço,
Pará, Brazil. Two different understory forest habitats were selected for sampling
on the basis of physiognomies: natural tree fall gap and undisturbed forest.
Twelve (12) sites were selected (6 natural gaps and 6 undisturbed continuous
forests). In each site, groups of 10 mist nets were set at ground level which
remained open from 6:00am to 2:00pm for two consecutive days, totaling six
days each month. This procedure lasted for 12 months and the sampling effort
totaled 23,040 mist net hours. All specimens captured were identified, marked
with metal rings and kept in cotton bags. We collected blood, feces and
regurgitation samples to determine the biomarkers of oxidative stress and the
composition of the diet. The relationship between thiobarbituric acid reactive
substances and the total antioxidant capacity was used as an index of oxidative
stress. The vegetation structure was determined based on transects along the
mist nets; the plants bearing fruits were identified and the total antioxidant
capacity was determined in each plant. Results: During the period of the study
347 specimens of 21 species were sampled. The assemblage of frugivorous
birds in natural gap is distinct from that of undisturbed forest sites. The species
responsible for dissimilarity were Dixiphia pipra, Pipra rubrocapilla and Turdus albicollis. The richness of birds was similar in both sites, but the availability of
fruits and the total capture index were higher in natural gaps. The primary
frugivores (those whose feces or regurgitation always showed fruit pulp or
seeds) occurred mainly in natural gaps, where the most abundant species was
Dixiphia pipra. In addition, Pipra rubrocapilla was the most abundant species in
undisturbed sites. Thirty-six (36) species of plants bearing fruits were recorded,
and the abundance of frugivorous birds was significantly correlated with the
number of plants bearing fruits in natural gaps, where the most common
species of plants were: Psychotria colorata and Psychotria iodotricha. On the
other hand, Faramea anisocalyx and Virola surinamensis were the most
common species in undisturbed sites. The variation of biomarkers of oxidative
stress in specimens presenting lek behavior varied with gender and to the site
of sampling. In natural gaps, the adult males of Dixiphia pipra showed higher
levels of oxidative stress. The high metabolic rate resulting of flight effort to
avoid predators, courtship behavior to the female and territory defense, can
increase the production of pro-oxidant compounds. However, the ingestion of
fruits with high content of antioxidant compounds by male can minimize the
deleterious effects of oxidative stress. The variance of oxidative stress of
species that do not have organization in leks was associated only with the site
of sampling. The specimens sampling in natural gaps showed higher levels of
oxidative stress. This can be due to the increase in metabolic rate to avoid
predators as well as new flight strategies for foraging.
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