Ecomorphological associations and abundance of birds across the agricultural landscape of Pothwar Plateau, Pakistan

Abstract

Some species are exceptionally common in landscapes heavily impacted by humans, such as agricultural lands. This studywas carried out over a period of 2 years (July 2012 to June 2014) in the arid agricultural landscape of Pothwar Plateau, Pakistan, toidentify adaptations that govern bird distribution and abundance across 2 different cropping systems associated with differences inwater availability. We used regular surveys and foraging observations to quantify species abundance, distribution, and habits. We thenexamined morphological correlations with ecological attributes. We found the following: (1) larger birds tended to spend more time intrees; (2) birds with small beaks and relatively long wings more commonly forage on the ground; (3) birds with narrow and long beaksand long tarsi were more likely to be insectivorous in habits. Of these associations, only the third axis, bill stubbiness and short tarsus,correlated with feeding on crops, implying that feeding on plant material is one preadaptation to crop exploitation. Bird abundancewas not correlated with feeding on crops. This is because some common species are crop exploiters, but other common species feed onsecondary growth (e.g., bulbuls, Pycnonotus spp.) or may be common in this region even in the absence of humans (e.g., the green beeeater, Merops orientalis). The best predictor of distribution was not crop-feeding but abundance. This appears to be because commonspecies feed on a set of resources that are common everywhere, whereas range-restricted species are found in areas with water—but evenin these areas, water is scarce.