Browsing by Author "Satish, Aditya"

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    The effect of disturbance-induced changes in vegetation structure and arthropod abundance on mixed-species bird flocks in the oak forests of the Western Himalaya
    (Wildlife Institute of India, Dehradun, 2024) Satish, Aditya; Page, Navendu; Bangal, Priti; Shahabuddin, Ghazala
    Mixed-species flocks are an interactive group of insectivorous birds that forage together and move in the same direction. Flocks provide foraging and anti-predatory benefits to participants. Habitat disturbance may affect flocks by – a) altering presence or abundance of participating birds in the community or b) altering flocking propensities of species. 2. I investigated the effects of habitat disturbance on flocks in the Western Himalaya of Uttarakhand, India. Disturbance was mediated through two mechanisms – changes in vegetation structure and arthropod abundance (food availability). I examined how these environmental variations impacted flocks at a community level through changes in flock richness, flock size, number of flocks encountered and flock composition. I also explored how flocking propensity (a species-specific tendency to join flocks) is impacted by these variables. 3. Flocks are a subset of the insectivorous bird community. I found that insectivore richness and abundance decreased with reduced structural complexity of vegetation caused by disturbance. Reduced structural complexity also led to a corresponding decline in flock richness, size and number of flocks encountered in disturbed sites. With regards to variation of flock composition with disturbance, I found no clear species-composition-based clustering in transects with similar disturbance levels. 4. There seems to be an interactive link between arthropods, insectivorous birds and disturbance. Disturbance was correlated with strong declines in foliage arthropod abundance, which in turn contributes to lower insectivore richness and abundance. Flying arthropod abundance largely remained constant with disturbance, so I would like to draw 2 attention to the effect of foliage arthropod abundance on flock variables in the following sections. 5. The number of flocks encountered increased with foliage arthropod abundance. Since insectivores in undisturbed sites are supported by a larger prey base, the higher frequency of flocking may be correlated to the larger pool of insectivores that are available to flock at a given time. I did not find significant effects of foliage arthropod abundance on flock richness and flock size. 6. I found that flocking propensity of the three most common species (Gray-hooded Warbler, Black-throated Tit and Green-backed Tit) in flocks showed a declining trend with higher disturbance. I also observed that the propensity of these species showed an increasing trend with higher foliage arthropod abundance. However, none of these relationships were statistically significant. More detailed research is recommended to investigate these preliminary patterns further, to better understand the complex interactions between propensity, disturbance and food availability. 7. To conclude, disturbance was found to have a negative impact on mixed-species flocks, primarily by altering the presence and abundance of insectivorous birds. From a habitat perspective, insectivores suffered declines due to the simplification of vegetation structure. Insectivores also face food scarcity as foliage arthropod abundance decreases. The combined effect of habitat loss and reduced food availability in disturbed sites leads to lower insectivore richness and abundance, which is in turn reflected in fewer, smaller and more species-poor flocks.