Of Storks In Farmlands
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.)
- Journal Article2016Factors affecting provisioning times of two stork species in lowland NepalWaterbirds, 39: 365-374. doi: http://dx.doi.org/10.1675/063.039.0406
The ecology of stork colonies in south Asia are very poorly understood. Factors affecting provisioning times by adults were evaluated at nests of two stork species, the Asian Openbill (Anastomus oscitans) and the Lesser Adjutant (Leptoptilos javanicus), in lowland Nepal where the landscape is dominated by multi-cropped agriculture fields. Analyses focused on understanding if provisioning times are influenced more due to colony-level variables, wetlands around colonies, or season. Using generalized additive mixed models and the information-theoretic approach, colony-level variables (brood size and chick age) showed non-trivial associations with provisioning times (substantially better than the null model). Univariate models with colony size and wetlands had poor support (worse than the null model). Season, which represented the changing cropping patterns, rainfall, and wetness on the landscape, was the most important variable for both species. The combination of season and wetlands was very important for provisioning Asian Openbills whose chicks fledged during the monsoon (July–October), but not for Lesser Adjutants whose chicks fledged in the drier winter months (November–February). Results strongly suggest that changing cropping patterns to a drier monsoonal crop, or reductions in wetland extents, will be detrimental to storks in Nepal.
- Thesis2015Food-provisioning behaviour in heronries in Rupandehi and Kapilbastu districts of NepalDissertation Submitted for the partial fulfillment of the requirements for Master of Science in Environment Science of Tribhuvan University Majoring in Biodiversity Conservation and Wildlife Management. Submitted to Department of Environmental Science Khwopa College ((Affiliated to Tribhuvan University), Nepal. 38pp.
Food provisioning is directly influenced by the availability of food resources around the nesting site and provisioning by the parents. This study was carried out to assess food provisioning in heronries with respect to i) water bird species, ii) chicks age iii) heronry size and iv) behaviour changes across the nesting season in Heronries during the 2014-15 nesting season. Study was carried out in 36 Village Development Committee (VDCs) of Rupandehi and 11 VDCs of Kapilbastu. Road routes were taken as transect for survey and covered once in 15 days during the entire nesting season (egg laying to fledging of chicks from nests; Aug 2014-Jan 2015). The food provisioning behaviour of Asian open bill (AOB) and Lesser Adjutant Stork (LAS) of varied sizes (Heronry size: no of nest in a tree) were taken for study. The food provisioning behaviour observations were carried out in the morning (6 am-12 pm) at 10-15 days interval in each heronry.
The average food provisioning time of AOB and LAS heronries was found to be 27.67±29.29 (n=341) and 38.13±49.99 (n=381) respectively. Both the species prefer short provisionig time i.e. more than 50% of provisioning time for both AOB heronries and LAS heronries was less than 20 minutes. The frequency percentage of provisioning time decreased continuously as the provisioning time increased at all stages of AOB as well as LAS heronry. Similarly, in case of heronry size for AOB heronries the average provisioning time was almost similar for all heronry size.and found to be not significantly different (χ2=0.93, P3,0.05=7.815). For LAS heronries the average provisioning time was high for heronry size 1 and size 5 and found to significantly different for heronry size (χ2=47.902, P14,0.05=12.592). Initially (first week of September) average provisioning time for AOB heronries was lowest and gradually increased till fledging of chick (late October). But in case of LAS heronries before October the average provisioning time was almost similar and increased from November to till fledging of chick (January).
Provisioning behaviour studies on waterbird species that form heronries are not available from Nepal, and are rare from South Asia. Thus outcome of this research would be step towards filling gap in ornithology and for understanding heronry ecology to help with planning, management and sustainable conservation of heronry birds in lowland of Nepal.
Keyword: Provisioning behaviour, Heronry, Nestling age, Heronry size vi
- Thesis2015Distribution, nesting trees preference and nesting success of heronries in Rupandehi and Kapilbastu districts, NepalA Dissertation prepared for partial fulfillment of the requirement of the Master of Science (M.Sc.) degree in Environmental Science of Tribhuvan University. Submitted to: Department of Environmental Science, Khwopa College (Affiliated to Tribhuvan University), Nepal. 48 pp.
The study was carried out in forty-seven VDCs of the adjoining districts, Rupandehi and Kapilbastu of lowland, southern Nepal. This study was focused on the distribution pattern of all heronries as well as for species, nesting trees preference relative to the overall availability on the overall landscape and nesting success of three species (LAS: Lesser Adjutant Stork Leptoptilos javanicus, AOB: Asian Openbill Anastomus oscitans and PH: Pond Heron Ardeola grayii) at heronries.
The survey was carried out from august 2014 with intensive survey of focal villages during visits of random points for nest tree preference. Bird species, tree species along with girth at breast height (GBH) and height were recorded. Altogether 75 heronries of AOB, LAS, CE: Cattle Egret Bubulcus ibis, PH, WNS: Woolly necked Stork Ciconia episcopus and RNI: Red naped Ibis Pseudibis papillosa were recorded. From Variance mean ratio (VMR), these heronries were distributed randomly. Similarly, AOB, LAS and CE were also distributed randomly as well. Heronries were distributed in all over the study area except some VDCs but they were sighted in those areas as well. AOB were distributed in six VDCs of Rupandehi while PH was distributed in two VDCs of Kapilbastu districts despite of this, their distribution pattern was random from VMR calculation. LAS and CE were distributed in both districts very well. They were also distributed randomly.
Bombax ceiba and Ficus religiosa were preferred by heronries as well as by individual species more than availability. Mangifera indica and Dalbergia sisoo were available most in the area. The preferred trees have more GBH (>200 cm) and height (>15 m) compared to random points. A single species appears to have different preferences based on the location of the study. CE preferred all range GBH trees than other bird species. The nesting success of AOB, LAS and PH were obtained to be nearly 95.12±15.8, 82.05±35.39 and 57±40.48 per heronries and the chicks fledge per nest for respective species was obtained to be 2.43±0.7, 1.51±0.69 and 1.32±1.42 respectively. There was negligible difference in numbers of chick fledged in case of AOB and LAS whereas PH has huge variation in numbers of chicks per nest.
Therefore, the landscape of lowland Nepal provides excellent condition for wide variety of large waterbirds to nest in heronries despite enormous human distribution.
Key words: Heronries, Distribution, Nest tree preference, Nesting Success.