Macho, macho ibis

The ibis is a wading bird with a long down-curved beak and a bare head. In some city locations ibis species are regarded as pests but there is also concern that the natural wetland habitats of ibis are being eroded. Now a new study has found that environmental contamination with mercury may be a threat to ibis reproduction.

Ecologists have recently published results of a study wherein they collected 160 ibis nestlings and split them into four groups, each of twenty males and twenty females. Once the nestlings were 90 days old they began adding methylmercury to their feed. One group received no mercury while the other three groups received either low, medium, or high doses.

The reason that this research was done was to establish the effect of mercury on ibis populations. The main sources of mercury in the environment are coal-fired power plants and gold mining. Once in the environment the metal is converted by some bacteria into methylmercury and it is usually found in wetlands. The levels of methylmercury used in the experiment were similar to what ibis would be exposed to in natural wetlands.

The researchers followed the ibis for three years and took blood and feather samples over the time. They found that mercury levels did build up in the birds and that exposure to mercury resulted in approximately fifteen per cent more nests that failed to produce offspring.

Male birds that had been exposed to mercury were less likely to engage in courtship behaviour and were also less likely to be approached by females when they did. Additionally, as levels of mercury increased so did rates of homosexual pairing.

It seems likely that methylmercury causes these behavioural changes by interfering with the hormonal system of the body and altering levels of sex hormones.

Not, of course, that there’s anything wrong with a homosexual pairing if it’s what an ibis genuinely wants…it’s just that is not going to do a heck of a lot for the propagation of ibis-kind if all ibis made that choice. It is just another reminder that every addition (or subtraction) from an ecosystem will have wider effects. The task facing humanity now, and thank goodness we are finally waking to it, is to make sure that our impacts are minimal or for the better for the planet.

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