Over the decade and more that I have been taking in and rearing baby birds, I have noticed and recorded a lot of changes in the species I care for, notably the decline in Greenfinch numbers seen in rescue centres, the times of year that certain illness and ailments are waxing and waning, the calcium deficiency increase in Collared Doves, plus Trichomoniasis and Young Bird Sickness in Wood Pigeons and over the last few years, the decline in the feather condition of baby Sparrows.
This Year it has been particularly noticeable and we currently have approximately 10 Sparrows in care with feather condition too poor for release. The young birds will have to stay in care until they moult a new set of feathers, probably next Year.
When we first started seeing this condition I assumed that similarly to Collared Doves it was a calcium deficiency and thought little more of it, giving the birds extra vitamins and minerals in their food to compensate. Then, over the last few years there have been more and more coming in with tatty, brittle, white feathers and I really had to start giving the cause more thought. The more I began to think about it the more I realised it couldn’t be calcium deficiency because unlike Collared Doves which begin breeding as early as January in the Uk (due to a lack of adaptability from their breeding patterns in Southern Europe from where they originated) and end up with Vitamin D deficiencies and resulting calcium issues, Sparrows who are native and breed in May and June should not be having these issues as there is no lack of Vitamin D by then.
I began to follow the RSPB research on the decline of Sparrows, which are now a red listed species in the UK and a study in Leicester has found that “Starvation of chicks due to lack of invertebrate prey was found to be the main cause of high levels of chick mortality in a declining suburban sparrow population in Leicester”
So, if lack of invertebrate prey is the issue, then those that are able to keep their chicks alive are presumably supplementing with other foods, probably seed from bird feeders and this may be the problem. As most rehabbers will know, all baby birds (including finches who grow into adults that eat seeds) need insects when they are growing as they need higher levels of proteins than seeds can provide. This seed supplementing, if that is what is happening, is missing the vital amino acids that biosynthesise the proteins needed and is therefore leading to Achromatosis caused particularly by Lysine deficiency.
The same RSPB study in Leicester found that
- Supplementary feeding of mealworms increased nesting success (fledglings produced per nesting attempt) by 55% in Leicester.
- Supplementary feeding of mealworms at 66 colonies in London increased breeding success (by 62%) but only had a small positive impact on colony size (adult abundance). Additional supplementary feeding of seed had no impact on the abundance of fledglings or adult sparrows. There seemed to be plenty of unoccupied suitable nesting sites in the London study areas.
The fact that supplemental feeding of seed had no impact but that supplemental feeding of insects improved fledging success, will in the long term be the key to the survival of our Sparrows in my humble opinion, unless we are able to redress the decline of our native insect populations, and that is a whole new battle.
In the meantime, all we as rehabbers, can do is to take in the affected fledglings and feed them plenty of insects up to the point of weaning (after which it would have no effect due to the growth period stopping) and then feed a healthy diet until the next moult.