Details arrived from the BTO of 2 Siskins caught in Will’s Garstang garden during our good Siskin catching sessions in early 2011, so I looked at other data from birds we caught during the period.
T879956 an adult male we caught on both the 18th and 22nd January 2011 was originally ringed at Gosforth Cumbria on 3 July 2008 as a recently fledged juvenile i.e bred locally. This is a distance of 76 kms only, with an elapsed time of 930/933 days.
X343298 an adult we caught on the same date as the previous bird on 22 January 2011, was first ringed at West Lexham, Norfolk on 14th February 2009, a distance of 265 kms and an elapsed time of 707 days.
Many of our winter Siskin are known to originate from the UK itself, but Siskins from Continental Europe winter here and also pass through much of the UK in varying numbers each year. The overall numbers may vary, relative to the Siskin’s unpredictable main food supply of cones and the seeds of birch and alder, which if low may cause an irruption of sorts as the birds seek out other food sources, at which times they may travel good distances.
The latter part of 2010/11 proved to be a "Siskin Winter", at least in the Garstang, Lancashire garden where they appeared in good numbers throughout January, February and most of March until both the actual numbers and daily throughput tailed off when the species headed north and east.
Throughout the three months Siskins arrived in the garden trees soon after dawn, probably from a roost in nearby woods, so from January onwards we decided to make a special effort to catch the species when the weather allowed mist netting. It was noticeable that the highest numbers of Siskins occurred not only in the few hours post dawn, but more so on wet or overcast days. This relates to the fact that Siskin are unable to feed on the damp or wet unopened cones during such weather conditions.
Siskins were first recorded using garden peanut feeders in the early 1960s, a habit that spread until the species is now a familiar sight in suburban gardens especially during the early part of the year and into March and April. Despite the Siskin’s reputation for liking peanuts, especially those in red mesh bags, our experience of recent years is that Siskins actually prefer using Niger seed feeders to peanut feeders. In his garden Will maintained an area of peanut and sunflower feeders, quite separate from a larger discrete patch of garden containing up to 14 feeders filled entirely with Niger seed,the objective being to attract Siskins only to this area so as to catch and ring as many as possible. The ploy worked by filtering out untargeted species from the netting area and allow Siskins full use of the feeders, where there would be less competition from the likes of Blue Tit, Great Tit, Chaffinch, Greenfinch, House Sparrow, Nuthatch, Coal Tit, and prior to the new year, Brambling. These less acrobatic, mainly larger species with bigger, less pointed bills cannot extract the tiny black Niger seeds from the pin holes of the feeder tubes, with the result being that they largely stuck to “their” section of the garden.
Subsequent to our ringing sessions and daily observations, the degree of how much the Siskin’s preference for Niger feeders was dictated by less competition around the feeders and how much by actual food preferences we cannot be sure, but they certainly homed in on the black stuff every morning.
In early 2011 we caught 258 new Siskins - 53 in January, 71 in February and 134 in March. (2 Siskins were caught at other sites, one bird at Rossall, Fleetwood and one at Out Rawcliffe, data for those two is not included here).
There were 36 recaptures - 4 in January, 21 in February and 11 in March. We also controlled 2 birds on 22 January, T879956 and X343298 both adult males, as detailed above. March 13th gave the biggest single catch of 85 birds with just 2 retraps on that particular day.
I broke down the 258 new captures and 36 retraps into sex and age specifics. Siskins are easy to sex and relatively easy to age at any time of year and the confidence level to the figures below is of 99% accuracy:
• Of the 258 new birds, 108 adults and 150 juvenile/first winter• Of 258 new birds 134 female and 124 male
• Of the 108 adults, 54 males and 54 females
• Of the 150 juveniles, 70 males and 80 females
• Of the 36 retraps, 17 adult birds and 19 juvenile/first winter
• Of the 17 adult retraps, 8 males and 9 females
• Of the 19 juvenile retraps, 4 males and 15 females
As might be expected, the age ratios favour juvenile/first winter birds but the figures show no major bias towards a majority of either sex in adults or juveniles, this ratio being virtually 1:1. Interestingly, but unlike the above data, most trapping studies of Siskins appear to show an imbalance of males to females, with more males to females in both adult and juvenile classes. The BTO’s recovery data also shows the imbalance and there is a suggestion of a differential migration of adults and juveniles that deserves further study.
In March it was noticeable that the Siskins were heavier than in previous months and that many carried visible fat, no doubt in preparation for migration. Average monthly weights:
• January 12.4 grams• February 12.5 grams
• March 12.9 grams
The ranges in weights were:
• January 10.9 - 15 grams• February10.9 - 14.9 grams
• March 10.6 - 15.7 grams.
No comments:
Post a Comment