There just aren’t enough palm tree homes to go around. Invasive ring-necked parakeets have prompted a rapid decline in Israel’s native hoopoe population, probably because of their aggressive takeover of nesting cavities in palm trees.

Reuven Yosef at Ben Gurion University, Israel, and colleagues followed densities of hoopoes in four palmeries in rural areas over a period of 10 years. In the two that were invaded by parakeets in 2000 and 2006, the team found a significant decline in hoopoe population density. By contrast, in the two palmeries without parakeets the hoopoe density remained unchanged.

These invasive parakeets usually nest in existing tree cavities. But in Israel they were observed digging new cavities, which suggests there is a lack of nesting sites. Parakeets start breeding earlier in the season than hoopoes do, and may use up all nesting sites before hoopoes can get to them, the team says.

Cavity competition

The results add to growing evidence of competition for suitable nesting cavities between ring-necked parakeets (Psittacula krameri) and native birds, including nuthatches, starlings and great tits. They may even be affecting bats.

Originally from Africa and South Asia, parakeets have spread globally, probably after individuals kept as pets escaped or were released into the wild. They are now a permanent fixture in cities like London.

But hoopoes in Europe are safe for now. “Currently, almost the entire European population of ring-necked parakeets is breeding in urban areas, whereas the hoopoes are generally not entering cities,” says Liviu Pârâu at Heidelberg University, Germany.

“The authors describe a local situation in Israel which cannot be generalised,” says Michael Wink at Heidelberg University. He says that in his experience there is no lack of nest holes and no apparent competition with native species in Germany, for example.

Journal reference:

Finding the way home

You pick up a harmless snake and it turns into a deadly viper.

This is what happened to from Sakaerat Environmental Research Station in Nakhon Ratchasima, Thailand, during a field trip with his team to a biodiversity hotspot in the north-east of the country where at least 176 snake species are found. He instinctively dropped it and the snake fled.

But it turns out Strine might have been fooled by a never-before-seen behaviour: a snake changing the shape of its eye pupils when attacked to resemble those of a deadly relation.

Further investigation revealed that the snake he picked up really was harmless: a mock viper (Psammodynastes pulverulentus) that has evolved several features to look like its venomous distant cousins, Malayan pit vipers (Calloselasma rhodostoma).

“Thailand is the land of mimics for snakes,” says Strine. “Most of the highly venomous snakes also have a non-venomous mimic counterpart.”

Eye spy

This is true of the mock viper, which has the triangular head, cryptic colour pattern and enlarged front teeth of its lethal relation. But it also appears to have gone a step further and evolved to change the shape of its rounded pupils into the vertical slits typical of a venomous viper when attacked.

Strine’s team was intrigued by the event and wanted to see it again. So, over the last four years of a biodiversity project in Thailand, they captured 36 individuals showing this behaviour.

One question is whether it evolved as part of the snake’s elaborate mimicry. “We are not even sure if it is a defensive strategy or just something that happens when the viper is gripped,” Strine says.

Another possibility is that vertical pupils appear less conspicuous, helping the snake obscure the outline of its head. Or it could be that constricting its pupils improves the mock viper’s vision, so increasing the accuracy of its defensive strike.

“I would love to look at this behaviour in a controlled lab setting because it may be that the behaviour has limitations based on aggressor species, stimuli and other environmental factors,” Strine says.

“It’s a very interesting observation but, as the authors say, it raises lots of questions,” says Gonçalo Rosa at the University of Nevada in Reno. “If this is indeed a defensive strategy for mock vipers, it is possible that we might find it in other species that share their habitat with true vipers.”