Why do birds roost in some trees but not others?

posted in: Roosting | 7

In a study on pest birds by Sodhi & Sharp (2006), the authors listed a number of tree species favoured by some of the more common birds as roosting trees. By late evenings, you could hear the loud, shrill cries around these trees as the birds swarm around preparing to roost in the trees. The noise continues for some time until the birds settled for the night. Early next morning the cacaphony of calls would start again until they fly off to their feeding grounds. The ground below these trees would be littered with their droppings and any cars parked below would be literally discoloured.

According to the authors, House Crows (Corvus splendens) favour roosting in tall trees with large dense crowns like Angsana (Pterocarpus indicus). These trees are usually surrounded by tall buildings that provide shelter against the weather and protection against predators.

Javan Mynas (Acridotheres javanicus) similarly prefer trees with dense crowns like those of Sea Apple (Syzygium grande) and Angsana. These trees should preferably be close to food centres and surrounded by vegetation. Again, these trees should provide shelter from the weather and protection from predators. These mynas either gather in large communal roosts or join mixed-species roosts that include Common Mynas (Acridotheres tristis), House Crows, Asian Glossy Starling (Aplonis panayensis) and Purple-backed Starlings (Sturnus sturninus).

So it is not just the species of trees that attract roosting birds but where they are planted. But then how many people are aware of this? Very few, and not even experienced birdwatchers from the Nature Society, who have been leading newbie’s on bird walks LINK.

I had the opportunity to make observations on the roosting of the Pink-necked Green-pigeons (Treron vernans) when they roosted in the Golden Penda (Xanthostemon chrysanthus) lining the road outside my house LINK. Admittedly the number of green-pigeons was not large but they confirmed the findings made by Sodhi & Sharp (2006).

The two trees they roosted in (above, arrowed) have dense crowns. On the side away from the road, tall vegetation provides shelter from the weather and protection from predators to these two trees. Another view of these two trees is shown in the image below (left). Compare these trees to the other image below (right), where the crown is just as dense but the tree is standing alone, with no vegetation around it. Thus no roosting pigeons.

Anyway, the roosting pigeons are now gone because of the noisy construction work to enlarge and cover the drains on both sides of the road, that went on for weeks on end.

YC Wee
Singapore
September 2014

Reference:
Sodhi, N.S. & I. Sharp, 2006. Winged invaders: Pest birds in the Asia Pacific. SNP Reference, Singapore. 184 pp.

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7 Responses

  1. Ben Tideas

    We have a tree where the myna birds roost, and have done so for many years. Driving around our suburb one sunset, I noticed there were 2 more trees within the area that they roosted in – along the route that I drove.

    So certainly, birds DO have their preferences, and while I don’t know the name of the tree, I’ve always called it the Happy Tree, despite the fact that these mynas have displaced a number of our native species.

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  2. Thanks for the feedback, Ben.

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  3. S Devsahayam

    Probably, its not the type of trees alone but their location also matters for communal roosting by birds. In many parts of India, communal roosting of mynas, crows, cormorants and many other birds is common near railway stations and intersections of busy highways on many trees under the glare of powerful lights and the cacophony of trains and other vehicles. Why do birds prefer such an disturbed environment compared to many idyllic and calm spots nearby? is it lack of predators or any other factor?

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  4. Safe from predators and protected from the elements are factors…

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  5. Abdulai Sulemana

    Hi there, if I want study the roosting behaviour of a bird (e.g. purple starling), what parameters/variables should I look out for and how should these parameters/variables be measured?…thank you

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  6. Singapore used to have mor rain forest trees around in the 60s. Notice all these trees were completely gone. They r the best species that mynahs and crows were not choose to roost in them. Palm trees or fir trees will be the best alternatives. Lavender and mint will be the best plants in Singapore to keep away mosquitoes and harmful insects. Singapore can consider for that that we also produce our lavender plants for oil and for tourist not just locate in Gardens by the bay. Lavender are great for planting on hills like mt Faber vicinity.

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  7. First, Singapore has not lost all its forest trees… Many species are used in urban plantings. About current roosting problems, these are due to the increase in the population of these birds (am referring to resident, not migratory species). They need to roost somewhere. The planting of trees along roadsides provide convenient roosting sites These birds prefer trees with dense foliage but in their absence, I am sure they will roost in palms and even “fir” trees. As for lavender plants, they are no indigenous to the region. You cannot just transfer them onto the ground and expect the plants to flourish on their own. You need to care for them all the time.

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