It’s a question I asked myself a number of years ago when noting how long it took for birds to discover new sources of food, in particular the introduction of bird feeders where none had been used previously.
Birds were always thought to have a very poor sense of smell. But most vultures and many scavenging seabirds locate their food by smell. Any birder who has been on a pelagic trip to see seabirds up close will be familiar with the practice of chucking overboard buckets of “chum” or “rubby dubby”, to lure shearwaters and petrels close to the boat. Scientists believe that other birds, e.g. homing pigeons, may use familiar odours in finding their way home or use their sense of smell during migratory journeys. Think about the various odours given off to overflying birds by different places, e.g. pine forest or ancient deciduous woodland, saline or fresh water, the urban jungle or the countryside.
A recent Dutch study determined that Great Tits found and located apple trees with winter moth infestations and big concentrations of caterpillars larvae by smell rather than sight. Tit species eat large numbers of insect larvae particularly during their breeding seasons when they feed them to their young, timing their breeding to do so. Trees benefit from the protection offered by birds removing larvae that would otherwise go on to eat the leaves and perhaps impact on tree growth and productivity.
The Dutch experiments were designed to remove other possible ways in which the Great Tits might detect the winter moth larvae. The researchers removed the caterpillars, removed leaves with holes and even took away signs of ‘caterpillar poo’, ensuring no visual clues were left for the birds to locate the infested trees. Despite these measures the Great Tits repeatedly found the trees with larvae infestations. The results were clear, even when they couldn’t see the trees, the Great Tits homed in on trees with winter moth infestations when they could smell them.
The researchers believe the trees gave off chemicals which birds can detect by smell to alert them to infestation. It has long been known that many plants attract insects using smells and benefit from the relationships as a result, but this is the first time they have been shown to attract birds in the same way. More research is needed to determine which chemicals are involved but infested trees were found to release more of a chemical responsible for the “green” smell of apples.
Most bird feeders use metal/plastic tubes or wire mesh to make the food highly visible to birds and we naturally assume that birds start to use our bird feeders because they locate food via their keen eyesight. My new niger seed feeders arrived today, replacements for ones recently stolen from a ringing site. At first glance the design looks improbable and unlikely to work as the feeding holes are tiny. When the stainless steel cylinder is filled with niger, the seed is virtually invisible with just the tiniest point of an individual seed poking through odd holes.
Nevertheless I experimented with this design of feeder a number of years ago and found them to be highly successful in attracting Goldfinches very quickly and I attributed this to the birds’ ability to smell the niger.
At lunchtime I took the new feeders to Oakenclough with fingers crossed that Scrooge doesn’t sniff them out before our ringing session which may well be tomorrow.
Here’s an experiment anyone can try at home. Buy a sealed bag of niger seed, Guizotia abyssinica, open the bag and stick your nose in it. Then inhale and enjoy the sweet, oily, nutty fragrance which brings in those Goldfinches.
No, there’s is no doubt in my mind that birds and in particular Goldfinches have well developed olfactory senses, probably as good as our own.
Now you must excuse me. I’m sure that from the kitchen I can detect the unmistakable aroma of a curry cooking in the oven and I'm ready for a bite to eat.
Linking today to Stewart's World Bird Wednesday.