RW Tree sparrow results

What have we learnt from the project?

Wetland edge habitat © Guy Anderson

We learned that the diet of Tree Sparrow chicks includes large numbers of insects that rely on water or very wet habitats. The insects included damselflies and stonefly nymphs, as well as large numbers of the Chironimid (non-biting) midges that so abundant around the reservoir. This was particularly the case in the diet of early season chicks (those in the nest in April and May).

Our ‘colonisation’ experiment, where we established new groups of nest boxes in the areas around the nature reserve, showed that local Tree Sparrows had a strong preference for nesting near the extensive wetland habitats around Rutland Water, and that they avoided sites on nearby drier, mixed farmland, further from the reservoir.
We also found that adult Tree Sparrows preferred to use a variety of wet areas (such as the edges of the reservoir, ponds and ditches) and woody vegetation (particularly hedges) to find food for their chicks, and tended to avoid the large areas of grassland available to them.

Table showing chick diet constituents

These findings suggest that wetland-edge habitats can play a key role in providing the diversity and abundance of insect food required by Tree Sparrows for successful chick rearing throughout their long breeding season (April to August).

Many remaining Tree Sparrow colonies in the southern and eastern UK are next to wetland habitats, with large areas of apparently unoccupied countryside between these wetland sites. This has not always been the case; Tree Sparrows have formally occupied a wide range of farmland habitats in the UK, and showed no particular association with wetland habitats. We suspect that many of these areas that were formally occupied can no longer provide enough insect food due to intensification of farming systems and increased land drainage in the late 20th Century. We are currently investigating this idea further by analysing the diet of Tree Sparrow chicks from sites around the UK in relation to their habitat: are successful Tree Sparrow colonies always associated with particular habitat types, wetland or otherwise? Results of these analyses will be posted when complete.

We conducted two breeding season surveys (in 2002 and 2003), of the areas surrounding Rutland Water, and found that Tree Sparrows in this area are restricted to colonies very close to significant wetlands and/or regular winter feeding. Much of the surrounding farmland did not hold any breeding Tree Sparrows, even though the colonies around Rutland Water are very productive and ‘export’ hundreds of young birds each year. It is unknown where most of these dispersing young birds end up. Some clearly go long distances: we have had one colour-ringed bird travel as far as the Suffolk Coast (163km!), and several others found up to 90 km from Rutland Water. It is possible that the others simply disperse away from the area, looking for other groups of Tree Sparrows to join, and never do so.

The importance of seed food, especially in winter, for Tree Sparrows, has been less easy to determine. Our colonisation experiment around Rutland Water showed no influence of seed feeders placed close to the nest boxes, on where birds chose to nest. Tree Sparrows are more wide ranging in winter than in the breeding season however, and it may be that all the Tree Sparrows breeding in our study area are quite capable of travelling a few kilometres in winter to find a regular food source, such as the permanent feeding station at the Egleton reserve. In other words, seed food was not a limiting factor for any of the breeding Tree Sparrows in our study area, but may be much more important on a larger geographic scale.

How our results translate into effective action for Tree Sparrows

Anything that increases winter seed food availability, preferably throughout the winter, close to (within 2-3km of) known breeding sites, will help tree sparrows. Appropriate measures could include weedy/grain rich over-winter stubbles, wildlife seed crops, sacrificial cereal crops, low input fodder crops, or managed feeding stations.

Furthermore, any measures that will provide more chick food in the breeding season should ideally be close to winter food provision, known winter flocks or nest box sites. Action related to existing colonies should be placed much closer (within 0.5-1km), since Tree Sparrows will rarely travel more than a few hundred metres when feeding chicks.

Measures that are likely to increase the number and diversity of potential chick food insects are; the creation of new hedges, and sympathetic management of existing ones; beetle banks, conservation headlands, and grass margins in arable fields; the creation of ponds and other wet areas; and low-input cropping and fallow fields allowing the growth of seed bearing weed-species through winter.

Providing extra nest sites (either nest boxes or through management of suitable trees or buildings) may help in areas where suitable nest sites are scarce, provided they are placed close to habitats that provide winter seed and summer insect food.

Recent good news

The latest monitoring figures produced by the BTO/RSPB/JNCC Breeding Bird Survey suggest that the decline of the Tree Sparrow in the UK has at least halted and that there is some recovery taking place, especially in the regions of the UK outside England. This is still a very long way below the 1970 population level, and we hope the recommendations we can make from our study will help to further improve the situation.

The work goes on

Tree Sparrow monitoring still continues on the reserve, conducted by members of Rutland Water Ringing Group, and although the formal scientific study has finished and results are being prepared for publication, valuable data is still being gathered as part of the Tree Sparrow chick ringing programme. One paper has already been published (Field & Anderson, 2004), further publications are in the pipeline and they will be posted here when available.

Thanks

Much of the work we have carried out would not have been possible without the substantial input of time and effort from many volunteers, both at Rutland Water and at other sites throughout the UK, thank you to them all! Thank you also to all the landowners who have allowed us access to their land to carry out these studies, and to J Denis Summers-Smith for inspiration and support.

Contacts

For more information, please contact Rob Field.
If you have seen a colour ringed Tree Sparrow please contact Rob, or go to the BTO website to report it online.