cherish your caterpillars

Cherish Your Caterpillars

More than half of all UK households provide food for garden birds. But many species are still struggling in urban areas. One of these is the blue tit. Studies have revealed that blue tits are not breeding as successfully in suburbia as they are in woodland locations. In some years, the breeding success of these birds has been incredibly low. Why should this be, given the provision of food and nesting boxes?

Good Nesting Diets

Scientists have long suspected that the issue may be the scarcity of a good nesting diets, which in the case of Blue tits means caterpillars. Whilst birds are attracted to urban areas by the food and nesting sites available, they then struggle to rear their young because of the ecological deficits. Blue tits are widespread in the UK and appear to do well in urban areas. However, their breeding success can be surprisingly poor. In 2015 it was found that the survival rate was as little as one chick per nest compared to up to five chicks per nest in rural locations.

Poor Breeding Rates

Biologists at the University of Glasgow and NERC's LSMSF Facility (National Environment Research Council's Life Sciences Mass Spectrometry Facility) have conducted a new study. The aim was to prove that a scarcity of caterpillars is the direct cause of poor breeding rates. The researchers counted caterpillars, other insects and spiders in areas where blue tits were known to forage. They found that the number of caterpillars in urban areas had greatly reduced and the typical seasonal peaks which enables chicks to thrive were absent.

Diligent Parents

The parent birds were filmed entering nesting boxes and it soon became apparent that the more caterpillars which were delivered to their young, the higher the survival rate was for the chicks. The blue tits in all regions were collecting food for their young but urban birds were feeding their chicks a large amount of replacement foods which the young find it hard to digest. It isn't every year that the birds suffered as badly as they did in 2015. But there is no doubt that urban birds are affected more severely by unfavourable conditions that those living in woodland.

The Importance of Biodiversity

It is clearly very important that the biodiversity of urban gardens is improved. This means that householders should plant wisely in order to promote insect life and that means the inclusion of native plants. Gardeners should also desist from the use of chemical pesticides. Many of the insects in our gardens are beneficial for birds and so it makes no sense to wipe them out. The number of pests will always be controlled naturally by birds and beneficial insects.


The aforementioned study strongly suggests that a deficit of caterpillars is a major issue. It is only one study and further research is necessary to establish whether or not the same problem can be found in different regions around the world. But it is likely that a lack of biodiversity will prove to problematic for many species of bird.

Back to blog

Leave a comment

Please note, comments need to be approved before they are published.