Dr Mark Brown, Nature's Valley Trust:
As a professional ornithologist I have studied nectar-feeding birds and the plants they pollinate for nearly 20 years. I have also conducted research on the impact of feeding birds in urban areas, and tried to examine the questions commonly raised, such as "do birds become dependent on my feeding?".Allow me to comment on some common misconceptions.
Firstly, sugar is not bad for birds at all. Nectar in flowers is almost purely sugar water, with very few exceptions. There are no vitamins, no proteins (very few birds actually ingest pollen at all), and no additional nutrients. Most flower nectar studied consists almost entirely of three main sugars, namely sucrose, glucose and fructose. Sucrose is a disaccharide sugar, composed of two monosaccharides, glucose and fructose. Plant nectars will either have sucrose, or glucose and fructose or a mixture of the three sugars in them. Sunbirds and sugar birds are very efficient at sugar digestion, extracting over 99% of the energy in such nectars (yes it has been measured!).
Birds have a much higher metabolism than ours – their body temperature is an incredible 42ºC, and with their large surface area to volume ratio (due to their small body size), they lose heat to the environment much quicker than us. This, coupled with their fast-paced flying lifestyle, means they need much higher energy loads than us.
A sunbird feeding on an average plant nectar will consume three times its body weight in a single day to maintain energy balance. We can't even consume 10% of our body weight in a day, so comparisons are pointless. The nectar in plants pollinated by sunbirds and sugar birds is typically in the range of 15 to 25% concentration, and those pollinated by occasional nectar-feeding birds like white-eyes, weavers, bulbuls etc is in the range of 8 to 15%.
Sunbirds need a minimum of 10% to meet energy requirements. Concerns that a higher concentration will attract insects have merit, but solutions 10 to 15% do not attract them often at all – the plants they pollinate typically have solutions with concentrations of 30 to 60%. Concentrations above 10% will not upset birds' stomachs – as is thought by some. As mentioned above, their natural nectar ranges from 15 to 25%, and you can even safely feed birds solutions up to 50% or more without ill effect.
There is one group of birds, starlings, that cannot digest sucrose, so when they feed on it they get osmotic diarrhoea, however, they learn this quickly and will avoid feeders once they have tried them a few times. The plants they pollinate, like aloes, red hot pokers and coral trees, have only glucose and fructose in their nectars. All other nutrients are achieved by other components of a bird's diet – even sunbirds and sugar birds include a high percentage of insects in their diet for example. A simple 10 to 20% plain table-sugar solution is, in fact, the closest natural mimic to natural nectar that you can get.
Secondly, birds do not become dependent on bird feeders. Flowers produce nectar constantly, and there are new flowers in an area all the time. In a transformed urban environment, there is no reason why not to constantly feed birds. There are little to no studies that show disruption to pollination systems in urban areas, simply because our nectar feeders form one small part of an individual bird's foraging range. My own work, pulsing between feeding and not feeding, with ringed birds (individually marked for identification), shows that birds do not become dependent on single feeders at all, but rather visit them as one stop along their daily feeding trips.
* For more information on responsible feeding tips for birds in urban areas, please visit the Garden Route Birds Facebook page – there are regular articles and tips posted there, and it is a wonderful platform to share your birds with others.
