What's behind spoonbills' deaths?

By Fang Lee-Shing 方力行  / 

Sat, Dec 14, 2002 - Page 8

How did the black-faced spoonbills die? It appears to be a mystery, but actually there are some clues we can follow up.

If, for example, the sick and dead birds have been discovered in the same area, they must have moved around in the same flock. Then the most likely cause of their deaths would be bad food.

If it is some pathogen that is killing the birds, they would fall ill at different times, depending on each bird's resistance to the disease. The birds would also probably die quite slowly. But if the birds are dying from a toxic substance in the food, they would probably die more quickly and at the same time.

But how did poisonous substances find their way into such a large number of fish simultaneously? Since spoonbills forage for food in the same area at the same time, toxic substances are the most likely cause of their illness.

What was the food? In the spoonbills' habitat on the estuary of the Tsengwen Creek in Tainan County, the most likely food is small fish and shrimps in shallow waters and commercial fish pools.

How and why would fish and shrimps be poisonous? In rivers, the practice of poisoning fish to catch them and wastewater from factories can introduce toxic substances into the food chain. But the environment around the Tsengwen Creek is not worthy of poisoning fish for profit. Nor is it a suitable place to establish factories. So it is most likely the birds ate fish that had been poisoned in fish pools.

Why are there poisoned fish and shrimps in the fish pools?

Fishermen usually discharge the water from their pools after harvesting the fish in them and use lime to sterilize the pools and kill the fish and shrimps remaining on the pool bed. After several weeks the pools are refilled and a new cycle begins.

However, some fishermen try to cut costs by using insecticide or potassium cyanate instead of lime. After two or three days, they wash out the ponds before introducing new fish.

Weather reports forecast cold weather for last week, prompting fishermen to harvest their fish to avoid losses. When the spoonbills arrived on their annual migration they most likely fed on the easy pickings found in fish pools or in drainage channels, where some of their prey may have recently died.

Since black-faced spoonbills usually choose remote places to feed, the fish ponds must be located near unfrequented beaches or in remote areas. We can test this theory by consulting bird-watching societies who study the areas where spoonbills feed.

With this information we can check who has recently harvested their fish from this area, and who is cleaning their fish ponds and with what. After comparing the residues from fish pools with samples from the stomachs and blood of the dead spoonbills, the truth might come to light.

How do I come up with these possibilities? In my research work, every day I see wild fish and shrimps poisoned to death, then egrets and water birds dying in the same way. But no one cares about them until famous birds, such as black-faced spoonbills, also become victims.

Fang Lee-shing is professor of marine resources at National Sun Yat-sen University.

Translated by Jackie Lin