Mariano Codesido

Distributional Changes of Landbird Species in Agroecosystems of Central Argentina

Abstract. We present the first quantitative comparative study between current (2006–2008) distributions of landbird and those recorded prior to the massive planting of transgenic soy beans in the Pampas of central Argentina (Narosky and Di Giacomo 1993). We surveyed landbirds along transects covering 23 counties of Buenos Aires province. To allow a comparison between our observations and those of Narosky and Di Giacomo, we used the number of counties in which each species was recorded as an estimate of current and past distributions. We found grassland and wetland specialists in significantly fewer counties than did Narosky and Di Giacomo (P < 0.05), while habitat generalists and woodland specialists showed no significant change. The earlier study, however, covered a longer period of time, which could explain the reduction of wetland dwellers as a result of variation in the supply of temporary water bodies. The decreased area of occupancy of grassland specialists, on the other hand, may reflect the reduction of native grasslands due to increased agricultural cultivation, particularly in the Rolling Pampa, where agricultural expansion has left few remnant grasslands and we did not detect three formerly common grassland specialists, Hymenops perspicillatus, Embernagra platensis, and Pseudoleistes virescens. These findings emphasize the need for conservation actions to support populations of grassland bird in the Pampas.

Agricultural land-use, avian nesting and rarity in the Pampas of central Argentina

Abstract Human-mediated changes in land-use have affected many bird species in South America, and other regions where agroecosystems are now the most common environments. We evaluate how the rarity of landbird species in agroecosystems is influenced by their specialisation in nesting habitat. We estimated rarity of species by their local abundance and area of occupancy in the Pampas of Argentina. Relative local abundance was positively associated with area of occupancy. Most rare species (9 of 14) were specialists, whereas 15 of the 21 common species were generalists. Both woodland and grassland specialists had smaller areas of occupancy than generalist species. This pattern was expected for woodland specialists, owing to a lack of woodland in the agroecosystems of the Pampas. In the case of grassland specialists, the pattern might reflect the destruction of natural grasslands owing to an increase of agriculture. Wetland specialists were an exception within specialists, probably because they share characteristics with common species, such as flocking behaviour and use different feeding habitats. Our results show that some grassland species of increased conservation concern in the Pampas are facing the threat of extinction associated with low local abundance and limited distribution, emphasising the need for further conservation effort

A contribution from Barn Owl pellets analysis to known micromammalian distributions in Buenos Aires province, Argentina

No abstract available

Seasonal variations in small mammal-landscape associations in temperate agroecosystems: a study case in Buenos Aires province, central Argentina

Abstract We studied the associations between small mammal assemblages and patterns of land use and landscape structure, and their seasonal variations in temperate agroecosystems. We collected barn owl, Tyto alba, pellets from nest sites located in the Pampean region included in Buenos Aires province (36 sites in winter and 29 in summer). We used Google Earth and SAC-C imagery classification to describe land use and landscape structure around pellet collection sites. In winter, we found a significant relation between the relative abundances of small mammal species and landscape variables. Landscape accounted for 33.2% of variance in species data. Calomys spp. were relatively more abundant in sites with higher winter crops cover, while Akodon azarae and Oligoryzomys flavescens increased their relative abundances in sites with more grassland cover. The commensal rodents Mus musculus and Rattus spp. were relatively more abundant in sites with higher urban cover, or near households and grain storage facilities. We found no significant small mammal-landscape association in summer. Our results are in agreement with previous studies showing that land use patterns may influence small mammal assemblages. Moreover, our results also show that seasonality plays a major role modulating the intensity of these small mammal-landscape associations in temperate agroecosystems.

Role of landscape elements on recent distributional expansion of European Starlings (Sturnus vulgaris) in agroecosystems of the Pampas, Argentina

ABSTRACT Previous studies of European Starlings in Argentina have focused on identifying biological aspects correlated with establishment of new populations in urban and suburban areas. Starlings have recently invaded rural areas in the Pampas. To understand the factors involved in the recent expansion of European Starlings into these rural habitats, we investigated how expansion patterns were associated with season, proportion of crop fields, distance to woodlots, and distance to small and big urban centers in agroecoystems of the Pampas. We surveyed 392 fields during 2011–2013 to collect data on presence of starlings and landscape features. We found that the range of European Starlings has expanded by a total area of ~65,000 km2 since 2005, at a linear range expansion rate of 22.2 km per year. Generalized linear mixed model analysis revealed that presence of European Starlings was significantly related with reduced distances to nearest small urban area. Our findings indicate that range expansion of European Starlings into rural areas of Argentina may follow a neighborhood diffusion pattern, by which well-established populations act as sources of individuals that disperse short distances into nearby favorable areas. In absence of human control, this species is expected to continue its spread and population increase.

Nest Building by Monk Parakeets Myiopsitta monachus in Urban Parks in Buenos Aires, Argentina: Are Tree Species Used Randomly?

Summary. The monk parakeet Myiopsitta monachus is a very successful invasive species and a worldwide agricultural pest. Knowledge of its nest tree selection could be a valuable pest control tool, given that its population expansion could be more effectively controlled by reducing potential nest tree availability. In this study we describe monk parakeet use and selection patterns of nest trees in five parks in Buenos Aires, Argentina. The species and structural characteristics of each nest tree was recorded. A census of potential nest trees was also performed to calculate Savages selectivity index for each tree species. We found 128 parakeet nests in 60 trees. The tree species selected by monk parakeets were cedars Cedrus atlantica, araucaria pines Araucaria sp. and palms (Butia capitata,Washingtonia robusta, Syagrus romanzoffiana, Phoenix sp.). Cedars were particularly selected as nest trees: they supported 40% of all nests and held more nests per tree than any other species. This is the first study to reveal that cedars and araucarias are selected by monk parakeets. Nest tree selection is a context-dependent process and it is guided by tree species and their structural characteristics and phenology. According to our findings, it would be advantageous to implement a careful selection of the tree species to be planted in Buenos Aires City parks and in urban areas elsewhere, in order to properly manage potential human-bird conflicts.

The Role of Stubble Type and Spilled Seed Biomass on the Abundance of Seed-Eating Birds in Agroecosystems

Summary. Croplands are habitats with high availability of food resources for seed-eating birds. The use of particular fields by birds may vary considerably depending on crop type. Some crop stubbles hold high amounts of spilled grain after harvest, which may support seed-eating bird populations throughout the year. We examined the role of crop stubble type and biomass of spilled grain on species richness and abundance of seed-eating birds in the Pampas of central Argentina. During 2011–13 we sampled 166 stubble fields: 77 fields during the austral spring-summer of 2011–12 and 2012–13 (44 wheat and 33 barley stubbles); and 89 fields during the austral autumn of 2012 and 2013 (49 soybean, 27 corn and 13 sunflower stubbles fields). We recorded birds on a 700 × 100 m transect and estimated spilled grain on 1 m2 of stubble cover in each field. Comparisons among species accumulation curves showed that wheat and barley stubbles had similar bird species richness in spring-summer, whereas in autumn, sunflower stubbles supported higher bird richness than soybean stubbles. Generalized linear mixed models revealed that the abundance of some seed-eating birds had significant associations with crop stubble types. Some species were positively associated with spilled grain biomass on particular stubble types. In general, these associations varied seasonally, being more evident in autumn than in spring-summer. Knowledge of bird species populations and their specific association with given food resources during periods when crops remain only as stubble could be a key tool to help plan management strategies designed to reduce bird impacts on agricultural crops prior to harvest, when they are most susceptible to significant levels of damage.