The Herts Tree Sparrow Project

For the past 30 years the Herts Bird Club, a branch of the Herts Natural History Society, has been supporting and protecting the last remaining breeding colony of Tree Sparrows in Hertfordshire at Tyttenhanger Gravel Pits near St Albans. Through year-round feeding, protection of key habitat and provision of nest boxes the Tree Sparrow population has stabilised after a decline of over 95% nationally since the 1970s.

The Early Years

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In response to the evident decline of Tree Sparrows in Herts, volunteers from the Herts Bird Club and Maple Cross Ringing Group began monitoring Tree Sparrows in the mid-1990s through the provision of nest boxes, recording of nest box breeding, and ringing and re-trapping of birds.

While nest boxes were erected in a number of traditional breeding locations and ringing was carried out at various sites, efforts soon became focussed on the last remaining breeding colony in Herts, at Tyttenhanger Gravel Pits on the edge of St Albans.  Two feeding stations were set up – one near Coursers Farm and the other by Tyttenhanger Farm – in areas of farmland but heavily quarried for gravel extraction.

With the support and help of local land managers – including Willows Farm and the then quarry managers, Lafarge Aggregates & Concrete UK – a program of supplementary winter-feeding and nest box provision saw the Tree Sparrow population stabilise.

Following a bumper year with 27 nests surveyed and 79 young fledged there were hopes that the birds might look to form a new sub-colony and expand their range.  However, while 2010 proved to be another good year for the birds the following years saw numbers return to lower figures.  It was clear that more needed to be understood about the needs of these sensitive birds.

More detail of these early surveys can be found in the project’s first reports published in 2009 and 2010.

Increased Efforts

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Starting in 2011, a pioneering monitoring program using electronic tags and loggers was introduced by the then Chairman of the Herts Bird Club, Ken Smith.  Small transponders (PIT tags), much like those used to chip pets, were attached to any adult Tree Sparrows caught during ringing sessions and to young birds in the nest boxes.  Any tagged bird would trigger a log every time it visited a feeder or (in time) nest box fitted with a logger.

After a few teething problems the loggers began to reveal new insights into the Tree Sparrows’ behaviour.  In particular the data, together with recoveries of ringed birds, revealed the highly dispersive nature of the Tree Sparrows with a significant movement of birds in and out of the Tyttenhanger population.  This new evidence indicated that one of the dangers facing the Tree Sparrow colony at Tyttenhanger was isolation, with the colony probably relying on input from colonies outside the area.

While it is still early days as far as data collection is concerned it is hoped that this ongoing monitoring will inform a better understanding of the behaviour of Tree Sparrows and what they need in order to survive.  Of course, not all birds are ringed and tagged so the picture given by the data is indicative rather than complete.

On-Going Work

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Volunteers from the Herts Bird Club have continued to support the Tree Sparrows to date involving visits to both feeder sites every couple of weeks to top up feed, maintain the feeders and nest boxes, and download the data log.

In the summer months nest boxes are surveyed weekly with all new Tree Sparrow chicks (pulli) ringed and tagged in the nest.  In the autumn and winter months adult birds are caught using mist nets and ringed.  In addition to the electronic PIT tag a standard BTO metal ring is placed on the bird’s other leg allowing the bird to be added to the BTO’s national database and identified if re-trapped somewhere else.

While the feeder at Coursers Farm is on private land the Tyttenhanger Farm feeder is close to a public footpath and local birdwatchers are encouraged to submit their records of Tree Sparrow sightings to the Herts Bird Club website.

These records help build up the picture further of where the Tree Sparrows are visiting and how many birds are involved.

In some years, birds have been seen nesting in natural holes in the area – e.g. in old trees – and it is possible that natural breeding like this could account for a small proportion of the population each year.