Browsing by Autor "Jennifer R. A. Cahill"

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An albino Gray-bellien Flowerpiercer ("Diglossa carbonaria") in the high Andes of Bolivia
(2008) Jennifer R. A. Cahill
Artificial Green Corridors in an Andean City as Effective Support of Avian Diversity
(Multidisciplinary Digital Publishing Institute, 2023) Alain Hambuckers; Johann Delcourt; Bryan Leborgne; Jennifer R. A. Cahill
Ensuring connectivity in the countryside and cities is a key element of nature protection, allowing genetic fluxes between populations in fragmented ecosystems. We tested the hypothesis that artificial green corridors are effective for birds in the city of Cochabamba (Bolivia). We compared the following aspects of natural corridors, with generally preserved vegetation, to those of artificial corridors, constituting parks and gardens in a matrix of streets densely planted with trees: species abundance and richness, functional diversity, and the traits of bird communities. We used canonical redundancy analysis to relate species abundance to the corridor type, noise, tree vegetation structure, richness, and functional diversity. We also tested the explanatory factors for relationships with bird species richness, functional diversity, and traits. We found that most species were shared between the corridor types; the corridor type, nevertheless, had significant effects, with bird species in the green corridors being more common and heavier and having a lower beak depth/mass. By contrast, noise-reflecting urbanization deeply affected all of the studied traits, indicating large shifts in species composition. In conclusion, green corridors seem reliable enough to maintain birds at a level almost comparable to that in linear corridors, but noise is a limiting factor for efficiency for both types.
Bird species richness in High-Andean forest fragments: habitat quality and topography matter
(2020) Constance Fastré; Diederik Strubbe; José Antonio Balderrama; Jennifer R. A. Cahill; Hannes Ledegen; Mauricio Torrico Orellana; Erik Matthysen
Montane forests worldwide are known centers of endemism and biodiversity but are highly threatened by fragmentation processes. Using data collected in 15 Polylepis forest remnants covering 2000 hectares, we investigated how bird species richness and bird community composition, particularly for species of conservation concern, are influenced by habitat quality and topography in the Tunari National Park in the High Andes of Bolivia. Bird species richness was highest in topographically complex, low-elevation Polylepis patches located in areas with a high potential to retain rainwater. Bird communities differed strongly between Polylepis lanata and P. subtusalbida remnants, each supporting different threatened and endemic species. Within the P. subtusalbida forest, high-elevation fragments characterized by high amounts of sunlight and low anthropogenic disturbance were more likely to contain threatened species. Surprisingly, we found no effect of fragment size on the diversity or composition of bird communities or the presence of bird species of conservation concern. The presence of exotic plantations (Pinus and/or Eucalyptus spp.) in or outside forest remnants was negatively associated with the number of bird species as well as with occurrence of the endangered Cochabamba-mountain finch (Compsospiza garleppi). To support the different communities found in Polylepis forests, these results suggest that conservation efforts should be directed towards both forest types (P. subtusalbida and P. lanata) present in the area. For an efficient management of avian diversity, exotic plantations should be established away from native remnants while existing patches should be managed to maintain or increase habitat quality. Finally, the importance of local topography in determining avian species richness and community composition in forest fragments, mainly through topographic controls on moisture distribution and the amount of sunlight received by the fragments, should be considered when planning conservation and reforestation schemes.
DESCRIPCIÓN DEL NIDO Y BIOLOGÍA DEL ANIDAMIENTO DEL TIJERAL LEONADO SYLVIORTHORHYNCHUS YANACENSIS EN BOSQUES DE POLYLEPIS BESSERI
(2024) Noemí Huanca; Lenny Terceros; Jennifer R. A. Cahill
Sylviorthorhynchus yanacensis es un residente especialista restringido a bosques de Polylepis de los Andes de Perú, Bolivia y Argentina. Aunque son necesarios los datos sobre su reproducción, aún hay escasos reportes sobre las características del nido y la biología del anidamiento. En el presente estudio, en un periodo de cuatro años (2002–2005) se registraron 54 nidos construidos sobre P. besseri en la Cordillera de Cochabamba, Bolivia. El nido se construye en cinco fases en forma de domo, con cuatro capas donde el material principal de las primeras tres capas son gramíneas altoandinas. El tamaño promedio de la puesta fue de 1,8 huevos, con un periodo de incubación de 21 a 24 días. Los polluelos permanecieron 21 días en el nido, con un cuidado parental que se extendió hasta ocho meses después que abandonaron el nido. El éxito de los nidos fue de 59%. El periodo reproductivo, tiempo de construcción del nido, anidamiento prolongado y la arquitectura del nido parecen estar influenciados por la época de lluvia y su frecuente descenso de la temperatura.
Genetic diversity of AndeanPolylepis(Rosaceae) woodlands and inferences regarding their fragmentation history
(Oxford University Press, 2013) Edgar E. Gareca; Peter Breyne; Katrien Vandepitte; Jennifer R. A. Cahill; Milton Fernández; Olivier Honnay
There is a long-standing debate on whether the occurrence of the iconic high-Andes Polylepis woodlands as small and isolated fragments is of natural or anthropogenic origin. We make inferences regarding the fragmentation history based on both a new population genetic study on P. besseri and a synthesis of available studies on the population genetics of Polylepis woodlands. We infer the timing of the main woodland fragmentation event by analysing: (1) the remaining levels of population genetic diversity and the relation to population size; (2) among-population genetic differentiation; and (3) the difference in genetic diversity between the offspring and adult generation. We retrieved seven publications on the population genetics of five Polylepis spp. We did not find a relationship between population size and genetic diversity, and genetic differentiation was low compared with that reported for similar plant species. These findings do not support a history of long-term fragmentation. The offspring showed a loss of genetic diversity and increasing differentiation compared with adults, suggesting that the main habitat fragmentation event is of relatively recent origin. For P. besseri, no significant differences were found between the adult and offspring genetic variation. We discuss the conservation and restoration consequences for this important high-Andean genus.
Habitat use by two specialist birds in high-Andean Polylepis forests
(Elsevier BV, 2007) Jennifer R. A. Cahill; Erik Matthysen
Home range characteristics of the Near Threatened Giant Conebill Oreomanes fraseri in fragmented Polylepis forest
(Cambridge University Press, 2009) Greet De Coster; Erik Matthysen; Jennifer R. A. Cahill; Luc Lens
Summary The Giant Conebill Oreomanes fraseri is a specialist of high Andean Polylepis forest remnants. With the aid of radio-tracking and visual observations, the average 100% minimum convex polygon home range size of seven adult individuals was 7.15 ha. Range size decreased with increasing tree density, and for equal tree densities, it was larger in the study site with larger Polylepis fragments. Home ranges often comprised areas that were largely or entirely devoid of trees. Within home ranges, space use significantly varied with time of day, and this pattern tended to be largely consistent among days. Given the large extent of variation in size and structure already observed in this small sample of home ranges, we suggest that apart from the size, shape, structure and degree of isolation of the remaining forest patches, also their topographic location, and hence sun exposure, may be an important consideration when designing conservation strategies for Giant Conebill.
Lower density of arthropod biomass in small high‐Andes Polylepis fragments affects habitat use in insectivorous birds
(Wiley, 2021) Jennifer R. A. Cahill; Thomas Merckx; Hans Van Dyck; Milton Fernández; Erik Matthysen
Abstract Polylepis forests are endemic to the high‐Andes, with trees characterized by multi‐layered, exfoliating bark‐providing protection against harsh, high‐elevation conditions, both for individual trees and the wide array of organisms dependent on them. However, Polylepis habitat has suffered severe human‐induced land conversion and currently mainly occurs as fragmented remnants only. Here, we studied the effects of fragment size on local ambient temperature and on biomass of bark and its bark‐dwelling arthropods. We did so by comparing multiple samples at the edge and interior of both large and small fragments, while also accounting for branch size, tree width, and tree structure. Because arthropod biomass is likely to impact higher trophic levels, we also studied abundance and foraging behavior of two bird species specialized on Polylepis forest. We show that arthropod biomass was relatively higher in wider, larger trees, which were preferred for foraging by both bird species. Moreover, we show that small forest fragments are not only environmentally less buffered but are also characterized by lower amounts of bark and lower densities of bark‐dwelling arthropods than larger fragments. Our study highlights the conservation value of large trees. Also, we advise it is now timely to test to what degree restoration efforts to increase fragment size could mitigate the negative effects of reduced arthropod biomass for higher trophic levels of endemic specialist insectivores.
Nesting biology of the Giant Conebill (Oreomanes fraseri) in the High Andes of Bolivia
(Wilson Ornithological Society, 2008) Jennifer R. A. Cahill; Erik Matthysen; Noemí Huanca
Eight nests of the Giant Conebill (Oreomanes fraseri, Family Thraupidae) were found in Polylepis forest fragments in Cochabamba Department (Sacha Loma and Cuturi) of Bolivia during 2002–2004. The breeding period of the Giant Conebill extended from September to December at the beginning of the rainy season. The nests were open cups with an average outside width of 20 cm and a thick rim of 5.5 cm; the average clutch size was 1.86. Nests were constructed mostly with parts of Polylepis trees and a variety of mosses. All nests located were in the interior of forests, well camouflaged, and in trees with an average height of 3.16 m. Control of human disturbance, especially burning, is needed for protection of the habitat of the Giant Conebill.
Network structure of avian mixed-species flocks decays with elevation and latitude across the Andes
(Royal Society, 2023) Flavia Montaño‐Centellas; Jenny Muñoz; Giselle Mangini; Ian J. Ausprey; Felicity L. Newell; Harrison H. Jones; María Elisa Fanjul; Boris A. Tinoco; Gabriel J. Colorado Z.; Jennifer R. A. Cahill
Birds in mixed-species flocks benefit from greater foraging efficiency and reduced predation, but also face costs related to competition and activity matching. Because this cost-benefit trade-off is context-dependent (e.g. abiotic conditions and habitat quality), the structure of flocks is expected to vary along elevational, latitudinal and disturbance gradients. Specifically, we predicted that the connectivity and cohesion of flocking networks would (i) decline towards tropical latitudes and lower elevations, where competition and activity matching costs are higher, and (ii) increase with lower forest cover and greater human disturbance. We analysed the structure of 84 flock networks across the Andes and assessed the effect of elevation, latitude, forest cover and human disturbance on network characteristics. We found that Andean flocks are overall open-membership systems (unstructured), though the extent of network structure varied across gradients. Elevation was the main predictor of structure, with more connected and less modular flocks upslope. As expected, flocks in areas with higher forest cover were less cohesive, with better defined flock subtypes. Flocks also varied across latitude and disturbance gradients as predicted, but effect sizes were small. Our findings indicate that the unstructured nature of Andean flocks might arise as a strategy to cope with harsh environmental conditions. This article is part of the theme issue 'Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes'.
Una diglosa carbonosa albina (Diglossa carbonaria) en los altos Andes de Bolivia
(2015) Jennifer R. A. Cahill
In February 2003 I observed a bird that appeared to be a completely white flowerpiercer (Diglossa sp.) foraging on the shrub Brachiotum microdon (Melastomataceae) along the edge of a 34.9-ha Polylepis forest fragment in Sacha Loma, Cochabamba department (Bolivia). The bird moved normally within the fragment, mostly through the central part containing a 10-ha boulder field. When flying across this area it became camouflaged against the background of grey boulders. I caught the albino, after 4 hrs of effort, with a 12-m mist net placed transversally in the boulder field.