Seasonal Fluctuations of Birds, Fruits, and Flowers in a Subtropical Forest of Argentina

Abstract

I quantified monthly variation in species composition and captures of birds in a premontane forest of northwestern Argentina. Seasonal patterns of frugivore-insectivores and nectarivores were compared with fruit and flower abundances, respectively. The composition of the entire bird community fluctuated seasonally; frugivore-insectivores showed a peak in captures during the wet season, insectivores peaked at the end of the dry season, and nectarivores peaked during the dry season. At a local scale (∼50 ha), captures of frugivore-insectivores were not correlated with number of plant species with ripe fruits for any vegetation stratum considered, but were correlated with a fruit phenology index that considers crop size. At a plot scale (∼7.5 ha), only understory flower abundance and captures of nectarivores were correlated, but only in the plot where both were more abundant. At a net-site scale (50 m2), captures of the Rufous-bellied Thrush (Turdus rufiventris) were correlated with understory fruit abundance, but only in the plot where fruits were more abundant. These results suggest that seasonal fluctuations in birds may be driven to some extent by their food resources. Premontane forest provides habitat for many migrants and also presumably acts as a source of birds that emigrate to disturbed areas. Although premontane forests should be a conservation priority for the region, they are poorly protected and suffering high deforestation.

Breeding biology of the Tropeiro Seedeater (Sporophila beltoni)

“…Breeding Phenology and Clutch Size Sporophila beltoni has a stable and well-defined breeding period (3.8 months), similar to other passerines in subtropical areas of South America (Malizia 2001, Fontana and Repenning 2014 as well as in temperate zones (3.1-4.2 months; Ricklefs 1966, Jones et al 2010. Sporophila beltoni, however, has a shorter breeding period than other congeners (S. collaris and S. hypoxantha, both resident in Formosa, Argentina, a warmer region; S. caerulescens and S. lineola, both migrant, in São Paulo, below 68 latitude) that have breeding periods of 5 months (Francisco 2006, Oliveira et al 2010.…”

Do Frugivores Respond to Fruit Harvest? An Experimental Study of Short-Term Responses

“…Addition of fruit to isolated populations of spiny rats (Proechimys semispinosus) in Panama increased rat reproductive success (Adler 1998). If the strong influence of fruit abundance found in these experimental studies represents a general pattern, then fruit abundance may explain frugivore abundance and behavior in foraging flocks (Chapman et al 1989, Develey andPeres 2000), in individual fruiting trees (Howe and Vande Kerckhove 1980), within and among habitats (Levey 1988, Loiselle and Blake 1993, Malizia 2001, Renton 2001, across regions and elevations (Levey and Stiles 1992, Stouffer and Bierregaard 1993, Rey 1995, Blake and Loiselle 2000, and through time (Martin and Karr 1986, Bronstein and Hoffmann 1987, Kinnaird et al 1996, Wright et al 1999. If the strong influence of fruit abundance found in these experimental studies represents a general pattern, then fruit abundance may explain frugivore abundance and behavior in foraging flocks (Chapman et al 1989, Develey andPeres 2000), in individual fruiting trees (Howe and Vande Kerckhove 1980), within and among habitats (Levey 1988, Loiselle and Blake 1993, Malizia 2001, Renton 2001, across regions and elevations (Levey and Stiles 1992, Stouffer and Bierregaard 1993, Rey 1995, Blake and Loiselle 2000, and through time (Martin and Karr 1986, Bronstein and Hoffmann 1987, Kinnaird et al 1996, Wright et al 1999.…”

“…Studies that have quantified fruit production have generally shown that frugivorous birds (i.e., species that include Ͼ50% fruit in their diet) are most abundant when and where fruits are most abundant (Wheelwright 1983, Levey 1988, Loiselle and Blake 1991, 1993, Jordano 1994, Powell and Bjork 1995, Rey 1995, Kinnaird et al 1996, Malizia 2001, Renton 2001; but see Herrera 1998). A major design constraint of these studies is that they are based on correlations.…”

Does landscape structure affect resource tracking by avian frugivores in a fragmented Afrotropical forest?

“…Map of the study area above 1200 m altitude (forest-shrubland boundary). Fruit tracking has been documented for obligate as well as partial frugivores (Malizia 2001) and by studying opportunistic frugivores with a broad fruit diet (typical of old world species; Dowsett-Lemaire 1988, Sun andMoermond 1997, Fleming 2005), tracking of overall fruit availability (i.e. Study plots are indicated with white squares (large fragments) and labels (all plots).…”