Is it time yet? Climate change disturbs breeding and nesting season in birds

  • Shifting seasons and unseasonal monsoon conditions have been affecting cues for the Sarus crane’s nesting season, a trend seen among other birds too.
  • Climate change is impacting birds like the Sarus crane but is still only one of the many drivers. Several species are being affected by a range of reasons such as pollution, habitat degradation, deforestation and most importantly, land use change.
  • Though in nascent stages, observations of the impact of climate change on birds is driving more research in India.

The arrival of monsoon rains in India is an annual milestone for the country. The blustery winds, loaded skies and torrential rains are signs of a good year not just for farmers and economists but also for the tallest of the world’s flying birds – the Sarus crane (Antigone antigone).

For these majestic birds, the onset of the rainy season in South Asia is a sign for the beginning of their seasonal nesting. However, shifting seasons and unseasonal monsoon conditions have been affecting these cues for nesting. A recent multi-year study across four Indian states showed that altered cropping and rainfall patterns are responsible for unseasonal nesting in Sarus cranes, a globally vulnerable species. Nesting of this species, outside the scheduled monsoon time, may also increase in response to intensifying changes.

Shifting seasons and unseasonal rains impact nesting season of the Sarus crane which relies on nature’s cues to start nesting. Photo by K. S. Gopi Sundar.

The study by K. S. Gopi Sundar, Mohammed Yaseen and Kandarp Kathju evaluated observations of unseasonal nesting of Sarus cranes from Haryana, Gujarat, Rajasthan and Uttar Pradesh between 2004 and 2017. Sundar, lead author on the study and director, Program SarusScape, International Crane Foundation, said that though from the observation of a few Sarus crane pairs nesting out of the usual rainy season, it might seem that this is beneficial, it isn’t so.

“There appears to be meagre evidence that Sarus cranes are able to capitalise on the changing rainfall patterns. Most years, no more than 40 to 50 percent of breeding pairs succeed in raising chicks. If the cranes were capitalising on the unseasonal rains, we should have seen a lot of the unsuccessful pairs trying to make the best of the new flooded conditions. But that is not the case. A very, very small number of pairs are nesting unseasonally implying that increased frequency of the changing rainfall pattern will not necessarily benefit these birds,” said Sundar.

Climate change disrupts nature’s timetable

The Sarus crane is not the only bird species whose life cycle is being affected by changing climate patterns. There is now an increasing body of research that illustrates changes in the timing of important ecological events, such as flowering in plants and reproduction in animals, in response to climate change.

There are several other examples from around the world of species in various landscapes and climates getting confused or triggered by untimely natural signals that have indicated the right times for nesting, breeding, foraging or migrating to more conducive climes. Shifting patterns and temperatures also mean that ranges of species are moving.

For instance, a similar study (to Sundar et al’s)  from Mauritius shows that the frequency of spring rainfall affects the timing of breeding, with birds breeding later in wetter springs. Delayed breeding means that these birds have reduced reproductive success as they get exposed to risks associated with adverse climatic conditions later on in the breeding season, reducing nesting success. These responses combined with the fact that frequency of spring rainfall had increased by about 60 percent in the east coast mountain range of Mauritius since 1962 does not bode well for nesting success.

Impact of changing patterns has been long recorded by bird watchers and citizen scientists. Such observations are driving more research. Photo by K. S. Gopi Sundar.

Another new study has pointed to the problem of an ecological “mismatch”  between the hatching of birds and peaks in caterpillar numbers, both linked to increase in spring warming in the United Kingdom. This means that warmer springs are creating a “mismatch” where hungry chicks are hatching too late to feed on abundant caterpillars, which are supposed to peak in numbers at the same time.

The researchers, from the Royal Society for the Protection of Birds (RSPB) and the universities of Exeter and Edinburgh, used data collected across the U.K. – largely by citizen scientists – to study spring emergence of oak tree leaves and caterpillars and the timing of nesting by three bird species: blue tits, great tits and pied flycatchers.

Malcolm Burgess, RSPB conservation scientist and honorary research fellow at the University of Exeter, said, “We were interested in these species because they are all woodland birds which are good examples to detect this kind of mismatch. These species have only one nesting attempt a year and timing of it is critical.”

What happens during spring is that the temperature triggers bud burst and the emergence of caterpillars that are then fed upon by the birds. “Yes, birds are adapting and nesting earlier as well. But there is a limit to it. We found that the earlier the spring, the less able birds are to breed earlier,” added Burgess.

In India, as well, though in very nascent stages, observations of the impact of climate change on birds are driving more research. “There has been research suggesting species range contraction, species range expansion in some cases, upslope movement to keep track of suitable temperatures. With the advent of the genomics era, questions are being asked if taxa can adapt to changes in climates, given their present levels of genetic variation. Are they even capable of adapting to new environmental scenarios? However, more research needs to be done in this front,” said Vijay Ramesh, a doctoral candidate at Columbia University, New York, who is looking into how climate and land-use has and will affect the endemic birds of the Western Ghats.

The impact of changing patterns has been long recorded by bird watchers and enthusiasts. “Over the last 30 years, we have been noticing some species of birds, whose distribution is not known from Kerala (considering historical distribution). Some of these were otherwise seen in northwest India or central Indian plains. These species started showing up occasionally initially but subsequently became quite regular. That led to us looking at where they are extending their range, if so what is the reason,” said P. O. Nameer, professor (wildlife) and head of the Centre for Wildlife Studies, College of Forestry, Kerala Agricultural University and a keen conductor of waterbird and eBird counts in Kerala.

Nameer points out the example of the pea fowl, a species that wasn’t there in earlier records during early 1970s and had been spotted very rarely only in the leeward side of the Western Ghats. “Kerala is wetter and denser than the habitat this species prefers that is more open and arid habitats,” he said. At present, Nameer is analysing last 100 years of weather and pea fowl sighting data. “We have made some preliminary distribution maps. And are using the eBird (citizen-led bird observational data) for analysing the voluminous data,” said Nameer.

Citizen science supports research around climate change and birds

The shift in species ranges (contraction or expansion) and distribution is a critical piece in these initial forays into investigations around climate change and birds. And citizen science is playing a large role in teasing out these connections. From Burgess to Nameer and Ramesh, all these scientists are using this data.

Ramesh is using a wide range of data to look at how ranges / distributions have moved. He is analysing data collected by British and American ornithologists and naturalists ranging from AO Hume to Hugh Whistler to Walter Koelz who spent decades of their lives in India (not restricted to the Western Ghats) collecting birds, taking detailed notes of where they were and when they were collected.

“The last decade has changed ornithology in India, with the boom of citizen science data, where birders go to a particular location, make a checklist along with ancillary information and upload it to Cornell’s eBird web portal. I will be using citizen science data to obtain a contemporary baseline of where these birds are found today. By comparing the two, one could definitely arrive at conclusions on how different factors in the environment, whether land-cover changes or climate change are affecting the changes in the distribution over time,” said Ramesh.

Indian bird experts agree that it is crucial to start integrating the impacts of climate change on birds in India, since we know  very little on how this has and will affect birds. Ramesh added, “Further, as mentioned earlier, the combined impacts of development and climate change could be dangerous to the survival of many of these endangered and endemic birds of India.”

In the larger picture, climate change is one among several factors impacting birds

Climate change is but one of the drivers impacting birds. Several species are being affected by a range of reasons such as pollution, habitat degradation, deforestation and most importantly, land use change. “In some cases, you see birds breeding way, way before the breeding season officially starts, but the question remains, if this is due to changing climates or other pressures such as habitat changes or competition for mates and resources,” said Ramesh. So, while climate change studies are critical, researching multiple drivers at various scales and over long time periods can divulge a more comprehensive picture.

While climate change is increasingly becoming a reason for changes in nature’s timetable and bird habits, there are several other reasons, most important land use changes, that impact birds. Photo by K. S. Gopi Sundar.

Sundar’s longterm research on Sarus cranes echoes similar concerns. That it isn’t just one impact, there are multiple drivers of changes in bird life cycles. “In general, changing climate alone is not necessarily providing short-term negative impacts, but increasing agriculture and changing cropping patterns are,” said Sundar. Climate change has, in some cases, also aided extra nesting seasons or range expansions in some species.

Sundar agrees that land use change is, by far, more urgent in terms of being a threat to bird populations (and also species diversity), relative to changing climate. “Climate change tends to take many more years to start impacting species (except in the case of very sensitive species, like those in the Himalayas that cannot tolerate even slight increases in temperature). The combination of the two – land use change and climate change – does not auger well for birds in general. We may see the survival of largely commensal species such as pigeons and kites that have adapted to human habitations and may well see the declines of species such as Sarus that need wetlands and wet crops for survival.”

Sundar, however, strikes an optimistic note in what seems like a downhill spiral for several species – that the example of the Sarus crane has shown how in South Asia farmers have aided and protected their nesting within their farmlands and that it is sometimes possible to find the right fit between our needs and other species’ needs in a human-dominated landscape. Sundar said, “The combined impacts of climate and land use change is seemingly many years in the future. The Indian rice-dominated areas continue yet to witness spectacular species such as the Sarus crane that is a grand example of coexistence and adaptability.”

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