Demographic outcomes of diverse behavioural strategies assessed in resident and migratory population of black kites Milvus migrans Phase VI

Abstract

The Black Kite, an opportunist, facultative scavenger in the South Asian urban ecosystems,； is a highly successful bird of prey, adapting to various habitats from natural landscapes to bustling cities (Fig.1 ).This adaptability makes them one of the most hutnerous raptors globally (Ferguson- Lees & Christie, 2001). In the Old World, these kites are resourceful and opportunistic eaters, thriving on abundant food sources from human refuse and prey species like pigeons and rats in urban areas. They readily exploit human-generated waste, allowing them to maintain a healthy population and favourable conservation status (Galushin, 1971). In Indian cities like Delhi, they reign as the top avian predators within the urban ecosystem. Studies since the 1960s suggest their breeding density has remained stable. While most raptors require specific ecological conditions, Black Kites exhibit remarkable flexibility (Kumar et al., 2020a). They primarily nest in trees, indicating a need for green spaces within the city. However, a small portion (less than 5%) utilise man-made structures for nesting (Fig. 2). The ample availability of trees in Delhi provides suitable nesting grounds (Kumar, 2013; Kumar et al., 2019). The abundance of garbage in cities - often amassing in the form of large landfills - provides kites with a readily available food source. Additionally, the positive attitude of residents in South Asia towards these birds allows them to breed undisturbed near human settlements. This human tolerance translates to moderate breeding success, with around half of breeding Fig. 1. A typical congregation of Black Kites in Old Delhi responding to ritual tossing of meat by Muslims that follow Sufi traditions (Jama Masjid area). Photo Credit: Fabrizio Sergio 2 BlacK Kite Project - Phase - VI pairs raising chicks to fledging (Kumar et al.t 2014). The high density of Black Kites in southern Asian breeding grounds offers a unique opportunity for research. Scientists can compare these populations to European Black Kites, which have been extensively studied since the 1950s. Pioneering research in the 1990s on European populations focused on factors influencing chick survival, including hatching order, sibling competition, and food availability. These studies have become benchmarks for raptor biologists (Ferguson-Lees & Christie, 2001; Newton, 1979). A crucial finding from European studies is the link between food availability and brood reduction (where some chicks die in the nest). When food is scarce, chicks compete more intensely, and some may not survive (Vinuela, 1996). Black Kites in Delhi exhibit hatching asynchrony (chicks hatching at different times) and brood reduction, likely influenced by the varying food availability across the city's diverse urban landscapes. To capture these ecological nuances, researchers have been using trail cameras in nests across different urbanisation gradients to study relationships with urban variables. These data are further combined with observations to assess hatching patterns, chick survival, growth rates, and nesting behaviour. Delhi hosts two subspecies of black kites: the resident breeding Milvus migrans govinda (small Indian kite) and the migratory M. m. lineatus (black-eared kite) that arrives from Central Asia and Southern Siberia via the Central Asian Flyway across the Himalayas. GPS-tagging revealed that M. m. lineatus kites migrate 3300-4700 km from their breeding grounds in Russia, Kazakhstan, Xinjiang (China) and Mongolia to Delhi in 3-4 weeks, crossing the Himalayas at elevations up to 5000-6000 m (Kumar et al., 2020b).