Bearded Tit Gritting Season Draws to A Close

The last few days have seen very little activity on the gritting trays at Leighton Moss RSPB Reserve. From September 23rd to November 27th we have recorded a total of 307 sightings of colour ringed birds involving 64 different individuals. Of these 36 were adult birds and 28 this years young.
We don't record every day but we have some interesting statistics on the number of visits birds make to the trays.Sixteen have been recorded on only one day. At the other end of the scale the most recorded bird was a juvenile female which visited on 15 days visiting first on September 30 and last on November 27th.
At each visit the birds sort through the grit which is mainly builders sharp sand. They can stop on the trays for up to 10-15 minutes and they appear to swallow regularly. This is in line with some research in Germany where they found an average of 609 small stones and a maximum of 850 stones in the gizzard in early winter when they are feeding mainly on reed seeds, but only 38 in spring when they turn to invertebrates.
One question I am often asked- Does this consumption of grit increase the birds weight. I looked at the weights of birds we have caught and weighed this year. In July the average weight of 22 birds was 14.1 gms. in October the average weigh of 40 birds was 15.2 and of 22 birds in November it was 15.7. So they have certainly increased their weight by around a gram and a half.Would need a much larger sample and a statistical test to prove the increase. But its interesting and does at first sight suggest that taking grit may well play a part in the increase.We have checked birds for any fat and there is very little.
John

Bearded Tits Still Gritting

Gritting continues especially on cold mornings. On Monday I recorded 14 different birds including 10 at once spread across the three grit trays at Leighton Moss RSPB Reserve. Difficult with so many birds present to work out pairings, all your attention goes into recording the colour ring combinations. They performed for ca ten minutes for an audience of 12 delighted birders, some who had never seen bearded Tits before. To date we have recorded 298 sightings of colour ringed birds involving 61 different birds. Of these 34 were adults and 27 birds hatched this year.Of the 61 35 were males and 26 females.

Yesterday though there were just four birds present, two apparent pairs. They gritted as pairs on separate trays. If any of the other pair attempted to join the other pair they were chased off.On checking their records I found they further proved what we have recorded on many occasions that Bearded Tits form pairs in their first autumn and if they survive they stay together through the year.

The first pair were hatched in spring 2015. They were first recorded together on 26th September and were recorded together on 5 occasions on the grit trays in October and November that year. This year they have been recorded together, either retrapped or sighted on the grit trays on 11 occasions.

The other pair were recorded together on seven occasions from late September to November in 2015.They we caught together on June 6th this year and have been recorded together on five occasions this October/November.

Very few other species form pairs early in life or remain together in successive winters.
John

Bearded Tit Gritting Season Continues

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