MIGRATORY birds are becoming vulnerable to shifts in seasons. Climate change is modifying the time of seasons. Early arrival of spring at breeding sites is making it harder for the migratory birds to attract mates or find food. Scientists warn this ecological mismatch can reduce bird populations.
The ecological mismatch has already put 84 per cent of bird species listed under Convention on the Conservation of Migratory Species under threat. For instance, Pied flycatcher that breeds in Europe and winters in sub-Saharan Africa and Siberian Crane, a critically endangered species, that breeds in Siberia and winters in China are already facing mismatch with local phenology.
The study by University of Milan was based on 117 migratory bird species that migrate from southern to northern Europe, covering 50 years. The researchers wanted to see if the spring arrival time of the birds at their breeding sites had changed. To study this, they used the birds’ average arrival days at a number of bird observatories in northern Europe.
The team then compared this information with the corresponding year’s degree days—total of average daily temperatures above a threshold that will trigger natural cycles, like plants coming into leaf or flower. The research was published in Proceedings of The Royal Society B.
They found mismatch was common. The team noted that the birds must optimise their arrival with the timing of spring. Arriving too early makes birds vulnerable to adverse weather and poor food supply. Late arrival increases competition for mates and territories.
So are the number of migratory birds on decline in India? Believes, Asad Rahmani, director of Bombay Natural History Society, “There is a massive decline in migratory birds like small waders (greenshank, curlew sandpiper) and ducks (Ferruginous, Red-crested Pochard).” He noted that climate change alongwith destruction of wetlands and extensive hunting can be blamed for this. L Shyamal, a Bengaluru-based naturalist said it is difficult to identify which of these factors is impacting the birds.
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