The Tyttenhanger Tree Sparrows
The Tree Sparrows at Tyttenhanger by and large conform to typical behavioural patterns but as a colony appear to survive in isolation. They also represent a very small colony of, on average 5-10 pairs during the breeding season. There is some evidence of immigration and emigration of birds from the colony from ringing recoveries but for the most part the colony must be under pressure to sustain itself.
Daily Routine
The Tyttenhanger sparrows operate out of two bases about 1.25km apart – one near Tyttenhanger Farm and the other near Coursers Farm. Central to these two sites are the feeders that contain loggers to record tagged birds visits. Data from the PIT tag logs have shown that while some birds have a clear preference for one site over another, other birds regularly utilize both.
The Tree Sparrows mainly nest in boxes erected by the Bird Club but in some years use nearby natural holes in dead trees. Most of the year small flocks spend the day flitting between feeders and the nearby thick hedges and occasionally commuting between sites or down to the reedy margins of the gravel pits. During the breeding season the sparrows are less noticeable with individual parents flying back and forth from the nest boxes to feed young.
An adult Tree Sparrow carrying nesting material to a hole in an old tree - photo Rupert Evershed
Maximum numbers observed on any one occasion tend to range from 20-30 birds post breeding, in the autumn and winter period. For example, in 2018 the maximum observed on any one day at the Tyttenhanger site was 25 in October and at Coursers, 30 in September.
The data has also shown that when one site is disturbed – eg through ringing activities – birds will fly to the other site. While the Tree Sparrows at Tyttenhanger Farm tolerate regular low-level disturbance from walks and dogs they are highly sensitive to higher levels of disturbance. A recent example was the laying of an underground cable near to the Courser’s site feeder that led to the Tree Sparrows vacating the site temporarily. Other species that visit the feeder such as Blue Tits and Yellowhammers still visited suggesting the sparrows are particularly sensitive to disturbance.
Breeding
Since the late 1990s the Tyttenhanger Tree Sparrows have been closely monitored and a nest box survey record kept each year. This record shows the sparrows success and productivity based on the number of nests built, the number of eggs laid and the number of young successfully fledged.
Breeding output varies year from year but on average over the last 20 years just under 50 birds have fledged each season. 2019 was the best year since 2009 with 67 birds fledged across both the Tyttenhanger and Coursers sites. It was also the first year in the last 9 years that Tree Sparrows used the nest boxes at Tyttenhanger Farm. During this 9 year period there were records of sparrows breeding nearby in natural holes but were not able to be surveyed.
In terms of breeding success (young fledged per egg laid), over the last 15 years has been on average at 56% while breeding productivity (young fledged per pair) has been on average 3.0.
The Nest Box Recording Scheme
