Since late September through to today we have recorded 255 colour ringed sightings of Bearded Tits almost all of them on grit trays along the Causeway at Leighton Moss RSPB Reserve. These have involved 59 different birds. Of these 33 were adults and 26 birds of the year. Of the 59, 33 were males and 26 females.
In our long term study of this species we have this year through retraps and sightings recorded 23 adult males and 18 adult females and 30 young birds making a total of 71 birds, so the 58 recorded gritting so far this season represents quite a large proportion of the known total population. These figures and those of the grit trays suggest that there are more males than females in the population. The catching of only 30 young suggests that productivity this year has been low and to date no unringed birds have been seen on the trays.
Past studies has shown that most birds visit the trays on under five days, but others make more visits with a record of 24 days by a first year female. Some birds visit early in the season then visit later presumably to top up the grit in their gizzards which they need this time of year as they change their diet from insects to the much harder reed seed. A German study found that in winter the average number of small stones in the gizzard was 609 with a maximum of 850, by contrast in spring they only averaged 38.
Gritting takes place usually between 08.00 and 12.00 and continues into mid December.
Sorry I have lots of photographs of the gritting behavior but for some reason the blog will not accept them.
John
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