Male brown-throated sunbird (above) and olive-backed sunbird (below)
We have two types of sunbird around our garden here in Thailand: the olive-backed and the brown-throated. They are both flower nectar-feeders and if you watch carefully on the right type of flower you can see them cheating the system.
Female olive-backed sunbird
The system is the exchange of sweet nectar from a plant for a pollination service to the plant. With some flowers the sunbirds get a free lunch by pecking a hole in the base of the flower and sipping the nectar from the outside without sticking their head anywhere near the flower's reproductive parts.
Poke a little hole in the base of the flower, open your beak to make it bigger, insert beak and drink nectar, check around to see if anybody noticed.
In our garden this is the way they always rob the yellow trumpetbush flowers. With some other types of flowers, like those of the orange tulip tree, the sunbirds do it properly and the plant benefits from the chance of fertilisation.
With the trumpetbush there are a lot of bees going through the flower's front door so in the end I don't think it really makes a difference to the plant. I am not sure why the sunbirds cheat with some flowers but not with others, it may be that they are not as good as hummingbirds at hovering so they do whatever is easiest whilst perching. Perhaps trumpetbush flowers are particularly easy to steal from - they do seem very thin.
Banana flowers are another plant where sunbirds bypass the plant's pollination system. Here, they don't have to poke a hole as the flower already has a gap they can insert their beak through. These flowers are actually designed for the nectar-drinking bats that come at night so again I don't think the plant notices, particularly as modern cultivars do not even need fertilisation to produce fruit.
These sunbirds tend to have brief bursts of feeding for a few minutes then stop for a rest and preen for about 10-15 minutes. Perhaps this allows the flowers to recharge their nectar supply.
The brown-throated sunbird is a bit larger than the olive-backed so they usually chase the smaller bird away from their favourite flower sources and occasionally chase them right out of the garden.
We have one plant that they take nectar from, the sea mango, where they do behave like hummingbirds hovering infront of the flowers while they quickly take a sip of nectar but they can only do so very briefly. I think this bush is a last resort as I don't see them feeding from it very often.
As well as drinking nectar they do also glean a few insects from the foliage, which is most obvious when they flit and hover around bushes that are not flowering. Another interesting part of their behaviour is the way they bathe in the film of dew that covers banana leaves early morning, although, in this hot, dry season there is hardly enough dew even for these tiny sunbirds.
I have also seen them taking nectar from two other flowering plants, including this silver palm, without needing to do any stealing. However, they do seem to spend most of their time robbing the trumpetbush flowers.
