Secondary seed dispersal by migrant harriers in India

Raptors or birds of prey are recognised as apex predators and key elements in food webs and ecosystem functioning. In this study, for the first time, we show that Harriers, one of the wide‐ranging migratory raptors with a strictly carnivorous diet, could effectively disperse seeds through secondary seed dispersal or diploendozoochory. The study identified seeds in 670 (21%) of the 3216 pellets collected from pallid harrier Circus macrourus and Montagu's harrier Circus pygargus winter roosts between 2016 and 2023 across three key wintering regions in India. The analysis revealed that harriers secondarily disperse intact seeds from 137 plant species across 23 families, including 64 monocots and 73 dicots . The mean seed count per pellet was 43.5 ± 2.9 (SD), with an average seed length of 2.6 ± 1.4 mm and width of 1.58 ± 0.9 mm. We sowed 6253 seeds to test the viability of seeds from the pellets of which 674 (11%) germinated, indicating that seeds of many species can survive the digestive enzymes in harriers' guts and suggesting their role in dispersing viable seeds. The study also identified seeds of eight crop species and three invasive species including Lantana camara in the pellets. The logistic regression analysis showed that the occurrence of seeds in the pellets was significantly associated with the co‐occurrence of birds and small mammalian prey. Our results demonstrate that the strictly carnivorous migratory harriers contribute to diploendozoochory in their wintering areas, potentially playing an important role in maintaining plant species distribution and richness in India's threatened open natural ecosystems.