ROLE OF CROP FIELD BOUNDARY VEGETATION IN POPULATION ECOLOGY OF PASSERINE BIRDS IN POTHWAR PLATEAU, PAKISTAN

Abstract

An agro-ecosystem demands intensive human activities related to farm operations to get optimum crop yield but such actions negatively affect local biodiversity including avifauna. Pothwar plateau of Pakistan covers an area of ~ 23,160 km2, totally dependent on rain water. About 110,600 haarea of the plateau is under cultivation while the rest of it contains scrub forest and rangeland. The agriculture consists of two major traditional cropping systems i.e. wheatmaize/millet and wheat-groundnut. Due to its unique topography and climatic conditions the plateau is famous for hosting important floral and faunal diversity of Pakistan. Like other regions of the country the Pothwar landscape is also under tremendous pressure of urbanization and agriculture expansion. An inverse relationship between agriculture expansion and loss of wild habitat is 15 reducing food and shelter to its native species including avifauna.This is causing many bird species (mostly Passeriformes) to adopt croplands for nesting, feeding and breeding. Since no reliable record of passerine birds associated with field boundary vegetation in this region is available therefore, the present study was conducted to investigate anthropogenic use, diversity and abundance of the cropfield- edge vegetation, seasonal diversity and species richness of passerine birds utilizing this vegetation for feeding, nesting and breeding. The study was carried out at four isolated patches of croplands, each covering an area of 1 km2. The anthropogenic practices were studied by interviews of 94 farmers and/or their workers. The farmers reported two main cropping systems i.e. wheat (intercropped with mustard) - groundnut and wheat-maize/millet. The livestock mainly consists of goats and cattle which are usually grazed on wild vegetation adjacent to the farmlands. Animal grazing in croplands is allowed after harvest or during pre-monsoon season. The farmers plant fast growing shrubs along crop field margins for fodder browse and fuel wood. Burningof crop residues and dry vegetation is not a common practice. Inorganic fertilizers commonly urea and DAP are used to enhance crop yield. Weeds, insect and rodent pests infest the food crops. Weeds are usually removed manually with some use of surface herbicides. Chemical control of insect and rodent pests is a popular practice while the farmers lackany knowledge on beneficial roles of birds in their croplands.Vegetation analysis revealed occurrence of 51 floral species on crop field boundariesincluding 12 tree species among which dominant were Acacia modesta and Zizyphus mauritiana, 14 species of shrubs and 25 species of herbs/grasses. Seasonal avian densities were estimated by point countswhich scored 25 species of birds including 20 resident and five migrants/winter visitorspecies. Most common and abundant bird species were house sparrow (Passer domesticus), common myna 16 (Acridotheres tristis), redvented bulbul (Pycnonotus cafer) and Himalayan bulbul (Pycnonotus leucogenys)while comparatively less common species were Indian tailor bird (Orthotomu ssutorius), common lark (Alauda arvensis), ashy drongo (Dicrurus leucophaeus) and ashy prinia (Prinia socialis). Other avian species were rare and confined to specific cropping systems. The migrants/winter visitors were recorded from November to March. Bird density and diversity decreased during summer due to absence of migratory birds as well as low availability of food. More numbers and species of birds were present at sites that had wheat-maize/millet cropping system and were in close proximity to rain water ponds which provide better living conditions to rare and infrequent birds in this arid ecosystem.Food habits of nine bird species determined by microhistological analysis of fecal droppings revealed that red-vented bulbul and Himalayan bulbul inhabiting this agro-ecosystem were frugivores. Ashy prinia, pied bushchat (Saxicola caprata) and ashy drongo fed exclusively on insects many of which are crop pests in this agro-ecosystem while common myna, common lark, large grey babbler (Turdoides malcolmi) and Indian tailorbird were omnivorous in their dietary habits. These species fed on wheat, maize and millet during some part of the year and they also visited crops for invertebrates particularly insects pests. None of these birds have status of pest in this agroecosystem. The breeding ecology of ashy prinia, red-vented bulbul, Himalayan bulbul, ashydrongo and large grey babbler revealed that prinia and the bulbuls utilized shrubs bordering the crop fields for nesting while drongos and babblers used the trees. The nests were constructed at low heights and were prone to ground predators like snakes and domestic cats while humans were also observed disturbing the eggs and nestlings of these birds. Due to these predators and general disturbance low hatching, fledging and breeding success of these species was observed in this agro-ecosystem. The study suggests enhancement and 17 conservation of roosting, foraging and nesting sites of birds in this arid agroecosystem region which could be accomplished by maintaining heterogeneity of native natural vegetation and patches of uncultivated land that act as bird refugeesas well as reduction in unwanted human activities and habitat degradation.