There was a time when California’s Central Valley held expansive wetlands ringed by riparian woodlands that together provided habitat for nearly two hundred species of wetland birds. Some used the Valley for breeding and nesting, others for overwintering, and others as simply a much-needed rest stop along the famous migratory route known as the Pacific Flyway. From spotted sandpipers to cinnamon teal and tundra swans, they all rely on soggy marshes buzzing with the diversity of life.

Today over 90% of those wetlands are gone, drained for agriculture and urbanisation, with only a few wildlife refuges preserving the remaining areas of original wetlands. Millions of waterbirds that used to occupy a much larger area are now packed into close quarters that increase the spread of disease—and the state’s historic five-year drought has only exacerbated the problem.

Over 80% of the flooded habitat in the Valley now comes not from natural wetlands but from agricultural rice fields. The hundreds of thousands of hectares of rice grown in the Valley are crucial to the health and survival of at least fifty species of waterbird. These birds consume the leftover grain that farmers would otherwise have to burn anyway, thus benefitting the farmers as well in a classic win-win.

Yet there is one major drawback. The extensive flooded fields create oxygen-deprived conditions in which microbes break down the leftover stubble and organic material of the previous year, and the chief waste product of this process in anoxic scenarios is methane—a greenhouse gas (GHG) four times more effective than carbon dioxide at trapping atmospheric heat.

The state of California passed the Global Warming Solutions Act in 2006 establishing their commitment to reducing GHG emissions to 1990 levels by the year 2020, and currently rice agriculture comprises 0.3% of California’s anthropogenic GHG emissions—a small percentage of the total, but when one considers the sheer amounts of GHG involved it is definitely nothing to sneeze at.

There are a few different techniques which rice farmers can use to reduce the amount of methane produced by their fields and California may create incentives for farmers to adopt these practices by incorporating them into the state’s Cap-and-Trade Program. One of these methods is to bale the majority of the leftover stubble instead of leaving it to break down in the water, while another option would be to reduce the amount of flooding in the fields and even allow them to dry out periodically. Either technique would reduce the amount of methane produced by the rice fields by around 23%.

While California’s desire to reduce GHG emissions and do their part to combat anthropogenic climate change is of course something to be commended, solutions to environmental problems are rarely that straightforward. Scientists who have been watching Central Valley’s wetlands dry up from the drought and who have seen populations of waterbirds decline in response worry that encouraging farmers to purposely remove vegetation or dry out their fields could have severe and unintended consequences.

When saving the planet can hurt wetland birds

Tundra swans in a California rice field. © Cheryl&Glen/Flikr

Recently, a team of researchers from Blue Point Conservation Science set out to determine how much the change in farming practices may affect the many waterbird species that depend heavily on the artificial wetlands that flooded rice fields create. Over the course of two years they conducted thousands of bird surveys on hundreds of rice paddies in the Central Valley including all possible combinations of farms that either did or didn’t reduce flooding and those that did or didn’t bale their fields.

The results of this extensive study were telling: rice paddies that either baled the excess organic material or reduced their amount of flooding supported significantly lower waterbird densities and lower bird diversity than those rice paddies that were fully flooded and not baled.

In other words, the farming practices intended to lower methane emissions also created lower-quality habitat that many waterbirds wouldn’t or couldn’t use. Maintaining a constant level of at least ankle-deep water coupled with a large enough supply of leftover stubble is what creates the ideal habitat that waterbird species can use for feeding, for protection from predators, for breeding and raising chicks—altering that landscape could make it completely unsuitable for their needs.

So is there any way to reduce the GHG emissions from rice agriculture without putting waterbird populations at risk? Potentially, yes. There is one more farming technique that reduces GHG emission, known as ‘drill seeding.’

This alternate method of planting allows farmers to decrease flooding only during the beginning of the season, before most of the migratory waterbirds have arrived, and then slowly bring the flooding up to standard levels in time for the migration. Drill seeding can reduce methane emissions by 16% and the study found no difference in waterbird usage between drill-seeded paddies and those seeded with more standard techniques.

Unfortunately, drill seeding requires specialised equipment that is currently too expensive for most rice farmers to afford—but if incentivised by California’s Cap-and-Trade Program, drill seeding could potentially be a good way to reduce methane emissions in rice fields without negatively impacting the waterbirds that depend on these manmade wetlands.

If California widely adopts baling and reduces flooding in order to reduce GHG emissions in rice fields, it’s possible that the Central Valley would lose much of the incredible diversity of waterbirds that it currently supports—although, one can argue that if anthropogenic climate change results in yet more devastating droughts, that would produce the same result.

Solving problems in conservation are almost never simple and often requiring balancing and/or prioritising conflicting goals. Should addressing the sweeping, global crisis of anthropogenic climate change come at the expense of local conservation concerns?

One fact is clear: research always needs to be done to make sure policymakers fully understand the potential impacts of their decisions, and it is crucial that those in charge of environmental management pay close attention to the warnings and advice of scientists. Only then can we do the greatest amount of good for both the planet and the wildlife that live on it.


Sesser, K.A. et al. (2016) Waterbird response to management practices in rice fields intended to reduce greenhouse gas emissions. Biological Conservation 197: 69-79. doi:10.1016/j.biocon.2016.02.021

Blankenbuehler, Paige (29/2/2016) “The disappearing wetlands in California’s Central Valley.” High Country News. 


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