Variation on species composition and richness in mixed bird flocks along an altitudinal gradient in the Central Andes of Colombia

Abstract

We recorded the species composition of mixed bird flocks, during 366 h of fieldwork in seven localities along an altitudinal gradient on the Central Andes of Colombia. We observed 164 species in 212 mixed bird flocks. Species composition varied along the altitudinal gradient and 27 species could have a cohesive role in the flock, but almost all of them were different among localities. The number of species per mixed flock varied from two to 30. The mean number of species per flock also varied among localities, and the differences among the whole set of species joining mixed flocks in each locality seem to be related with both differences in altitude and geographic distance.

Multinomial-Poisson mixture models reveal unexpected higher density estimates of an Andean threatened bird

“…This pattern could be explained by natural history and habitat requirements of this species as it prefers dense cloud forests where forages in subcanopy and canopy strata, which difficult its observation (Hilty and Brown, 2001;Angarita and Renjifo, 2002). Furthermore, the Multicolored Tanager is vocally active when joining to mixed-species flocks (Marín-Gómez and Arbeláez-Cortés, 2015), where pairs emit constant short contact calls and males sing for few time intervals (Marín-Gómez obs. pers).…”

“…This tanager is restricted to montane forests between 900 and 2200 m of the Western and Central Andes of Colombia, and inhabits primary forests, forest edges, and second growth forests (Collar et al, 1992;Hilty and Brown, 2001;Angarita and Renjifo, 2002). The species forages in pairs in the sub-canopy eating fruits of species of Cordia, Miconia, Palicourea, and Ficus (Collar et al, 1992), searching larvae in bromeliads (Cuervo et al, 2008), gleaning underside of leaves (Isler and Isler 1987), and joining to mixed-species flocks (Marín-Gómez and Arbeláez-Cortés, 2015). The population density of the Multicolored Tanager is low compared to other tanager species (Collar et al, 1992) as a result of the fragmentation and loss of 79.3% of its habitat (Renjifo et al, 2014).…”

“…Despite being a colorful bird, the Multicolored Tanager is relatively difficult to detected during point counts sampling, due to its secretive behavior and rapid foraging movements in the canopy (Cárdenas et al, 2007;Fierro-Calderón et al, 2009;Marín-Gómez and Arbeláez-Cortés, 2015). Thus, its lower detectability could be related with sampling efforts, and differences in habitat use, breeding period, and fruit availability (Fierro-Calderón and Johnston-González, 2014).…”

Network structure of avian mixed-species flocks decays with elevation and latitude across the Andes

“…Because the benefits of flocking are context-specific and expected to vary with environmental conditions and flock mates [12][13][14][15], the composition, behaviour and structure of flocks (i.e. how species associate with each other) will change across environmental gradients, such as elevation [16][17][18], latitude [19] and human disturbance [12,20,21]. One proposed mechanism for these changes in flock structure is that the role of facilitative interactions in biological communities should increase with the harshness of environmental conditions [22][23][24] (i.e.…”

“…The Andes of South America is the longest mountain chain in the world and presents an ideal opportunity to assess how stressful environmental conditions influence the structure of flocks. In the Andes, environmental conditions change drastically over greater than 3000 m of elevation and 9000 km of latitude, affecting flocking behaviour and prevalence [16][17][18][19]. Species inhabiting harsher environments at higher elevations and latitudes, theoretically, have metabolic adaptions to low temperatures [28,29] that might cause subsequent increases in foraging rate and reductions in vigilance [30], two behaviours thought to promote flocking activity.…”