Asian Openbills and Lesser Adjutants feeding in a Nepali SarusScape
Birds living in south Asian agricultural landscapes face strong seasonality in weather and crops, and wetlands they share with millions of humans. To find out how they cope, we studied the feeding behaviour of two Stork species in lowland Nepal.
(April, 2017.) Lowland Nepal is nearly entirely converted to agriculture. However, Nepali farmers still retain a lot of trees and wetlands amid cultivation. We explored the potential benefits this "working landscape" around Lumbini has to offer to two stork species.
Despite hosting crops almost throughout the year, this area supports hitherto unknown numbers of breeding stork colonies. We investigated the factors that affected foraging behaviour of two breeding stork species - the abundant Asian Openbill, and the globally-threatened Lesser Adjutant.
Changing crops (monsoonal rice and mixed cropping in the winter), was a strong influence on foraging behaviour and breeding success of both stork species.
Wetlands were rare on the landscape, and experienced enormous human use throughout the year. In some respects, the dominant agriculture appeared to overwhelm the utility of wetlands as feeding habitat, but in other respects, wetlands in combination with the current cropping pattern were helping storks find food.
The extensively cultivated landscape of lowland Nepal has cropping patterns and wetland use that are facilitating conservation of impressive populations of Asian Openbills and Lesser Adjutants. Finding mechanisms to continue this fortuitous coexistence of humans and wildlife will be critical to the continued survival of these large waterbirds.
Storks amid agriculture
Large waterbirds such as storks live alongside cranes in many countries. In south Asian SarusScapes, a number of stork species share the landscape with Sarus Cranes, but little is known of the ability of these areas to support storks.
We began exploring central, lowland Nepal in 2013 as part of our long-term monitoring effort. We discovered that the neighbouring districts of Rupandehi and Kapilabastu were home to a very large number of storks - much more than was known before.
Two of the most abundant species were the Asian Openbill and the Lesser Adjutant. This is their story.
Contrary to what is known about these two stork species, it became evident that they were proliferating in this heavily-cultivated area breeding in impressive numbers.
Were the remaining wetlands key to the survival of these storks? What were the other factors driving stork behaviour and breeding success? To try and answer these questions, we instituted two Masters-level dissertation projects for students from Khwopa College in Bhaktapur, Nepal.
Bijay Maharjan focused on one behaviour - the time it took for adult storks to get back to nests with food. In this post, we focus on what he discovered. Roshila Koju focused on breedings success - more on that will be posted later. Both presumed that habitat in the larger landscape, cropping patterns, presence of human habitation, as well as aspects of the colony itself (e.g. colony size), affected storks.
Finding the colonies and setting the stage
Conducting the first study in an area is exciting, but this comes with some challenges. Bijay and Roshila had to first find out if there were enough colonies for the study, and where they were located. Both, along with our field associate Kailash Jaiswal, scoured the farmlands using the road network. They spent the best part of a month traipsing back and forth on roads slippery with mud and generously dotted with pot-holes. The effort paid off!
We ended up with an unprecedented discovery: 74 waterbird colonies were located in an area of about 800 sq-km. The discovery included 14 Asian Openbill colonies and a staggering 35 Lesser Adjutant colonies!
As the work in the field progressed, back in Delhi, we used satellite imageries to figure out details about the landscape. Agriculture dominated this area (~85%), with the rest comprising human habitation (3%), wooded areas (7%), and wetlands were scarce (2.5%).
Using field data of colony locations and the satellite imageries, we measured the amount of wetlands and human habitation around each colony. We wanted to see if birds in colonies with more wetlands around them did better, and if human presence was a deterrent.
Bijay, Roshila and Kailash worked for five months timing adult birds as they returned to nests with food. How long they took to return with food was our metric of choice - shorter trips would suggest they are getting a lot of food.
Foraging behaviour: it's complicated, yet not!
Bijay, Roshila and Kailash were able to observe adult storks returning to nests with food nearly 700 times for both species combined. This added up to 23,230 minutes!
Time taken for storks to find food and return increased and decreased several times over the season. On average, Asian Openbills needed 26 minutes to return with food, but Lesser Adjutants needed 38 minutes.
For both species, the progression of the season was the single-most important reason affecting return times. It appeared that cropping practices going on during the nesting - harvest of rice, planting of wheat and other crops, and so on - was causing food availability to change.
The analyses also highlighted some complexity. Wetlands in combination with other variables, such as colony size (for Lesser Adjutants) and season (for both species), were very important in influencing return times. This was clear evidence that wetlands are important, given current landscape conditions!
This is also an unambiguous red flag: further declines of wetlands will be detrimental to stork foraging. Also, if land use changes convert croplands to more human-dominated features, storks will suffer.
Surprisingly, wetlands around colonies by themselves did not influence return times too much. This could mean
two things. One, that the dominant crops are overwhelming the potential benefits that the much-rarer wetlands offer. Alternatively,
there is enough food in the cropfields for current populations of both stork species.
What it all means
The agricultural landscape of lowland Nepal is able to support the feeding of hundreds of breeding Asian Openbills and Lesser Adjutants. This is great news, especially for the latter species which is a globally-threatened species.
Not surprisingly, the impact of humans on both feeding behaviour and breeding success, was strongly visible.
The dominant croplands are beginning to overwhelm the benefits afforded by wetlands. But the wetlands are still holding out, and providing clear benefits to the storks.
Wetlands in lowland Nepal are very useful for humans, and now we know that at least two stork species need them too. Ensuring that wetlands persist, and are not allowed to be drained, is a win-win for humans and wildlife.
In association with the wetlands, the current cropping pattern and agricultural practices are also important for the situation we are unraveling. Admittedly, we know almost nothing about what drives the current agricultural practices, and we hope to find out more soon.
Finally, a lot of the existing literature assume the needs of the storks incorrectly. All suggest that agriculture is always detrimental to the birds. Fortunately this is not the case.
Storks, and other waterbirds, can be beacons to highlight the accidental but very welcome coexistence of farmers and birds in Nepal. We hope our future work will uncover the limits of this coexistence to the benefit of this happy coexistence.
Getting it all done
Bijay, Roshila, Kamal and Kailash endured mental anguish and personal losses in the debilitating 2015 earthquake, but emerged as stronger, better human beings.
Since then, they have also endured near-continuous political instability, and an embargo on even essential commodities like fuel for vehicles and cooking.
Political instability alongside absence of basic amenities including electricity and internet connectivity slowed communications. Also, Roshila, Bijay and Kamal enrolled into new jobs rendering time a rare commodity.
But we plodded on to ensure that the hard work on the field could be converted to two important outputs - Masters theses, and published papers.
By early 2017, when this story was written, we had achieved most of our plans.
It has been a real pleasure to work with our Nepali colleagues, and the outputs we have completed is a testament to their ability to flourish even amid great odds.
Gopi & Swati.
(Photographs used in this post are by Bijay Maharjan, Roshila Koju and Gopi Sundar.)