This morning I cut a single orange in half, and placed it on the fruit feeder. Within 30 seconds, several visitors had arrived and a pecking order had been established. It triggered a thought – what makes that orange so attractive (and we can observe that even more excitement is generated in winter). The immediate mental response was “energy”. And so I researched.
Let us take the Black-fronted Bulbul as an example. At times the energy requirements are massive (e.g. breeding season). A typical number will be 3000kJ/kg/day. considering the mass at around 1/30 kg, it means that this little bird needs 100kJ per day for normal maintenance. In contrast, humans need 200kJ/kg/day (perhaps typically 15000kJ) per day. The bulbul needs 15x more energy in proportion to humans! Well a typical large orange has 300kJ of energy. The bulbul in this example needs at least the equivalent of one third of an orange per day – probably double own weight by my arithmetic! Sadly, the Grey Louries were never going to give the bulbuls a chance to feed today (fortunately, we also had other titbits for them!)
Now, for non-passerine birds the energy requirement values are lower. Also, in non-breeding season, my guess is that the requirement will come down 20 - 30%. All the same, the conclusion is that your garden birds will flock to a regular energy source when it becomes more difficult to find the source in the natural environment. Obviously, in winter, times are tougher. It is borne out by what we see on our feeder. All the birds are desperate at present – so give them some love at your feeding point! (And there is no greater love than Elaine’s Suet for wild birds – very high in both energy and protein!)
