Fat Is Good

In amongst the 60+ Siskins caught since Christmas at Oakenclough have been a number with visible fat reserves. Ringers regularly check the birds they handle for visible fat, especially during the winter or at times of migration when high scores can indicate that an individual is in the process of migrating or building up reserves during a bad spell of cold weather. One memorable Siskin of 31st March 2016 tipped the scales at 16.2 grams - Another Bird Blog.

It’s not often there are Siskins in my garden, even in a “Siskin Winter”, a year when the species becomes especially numerous in the early months of the year. If it was going to happen again then 2016 would be likely as good numbers have been reported in many parts of the UK, more so in recent days as large numbers of migratory Siskins head north. 

Today I caught another fat Siskin, a second year female, this time in the garden. This lovely lady weighed a stupendous 16.8 grams, amazing when you think a tiny Siskin normally weighs between 11 and 12 grams. It becomes more remarkable when considering that the bird probably accumulated this amount of extra fat in just a couple of days of short refuelling stops and increased her weight by 30 - 40%. For migrating birds ... it pays to be fat! 

Siskin - second year female at 16.8 gms

Siskin - second year female

Research has shown the strategy allows them to reach their breeding grounds faster and claim the best nesting sites. Small migratory birds sometimes need to take a break to replenish their fat reserves, especially after crossing vast oceans or deserts. Factors known to influence the length of these stopovers are the weather, food availability and internal factors such as a genetically programmed urge to continue the journey. 

The last time I witnessed the build-up of Siskin fat reserves was in the early part of 2011, the last "Siskin Winter" when Will and I caught good numbers in a Garstang garden. Garstang is just a few miles from the current ringing site of Oakenclough, one of the reasons that we chose to re-establish a ringing site here when Will moved from the old location.

In early 2011 we caught 258 new Siskins - 53 in January, 71 in February and 134 in March.  During March it was noticeable that the Siskins were heavier than in previous months and that many carried visible fat for migration purposes.

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.

In the garden at home this past weekend the normally ever present Goldfinches have mostly moved out, replaced by small numbers of Siskins and Lesser Redpolls, although both species moved quickly on after devouring quantities of Niger seed. 

Siskin

Goldfinch

Last week’s Nuthatches seems not to have stayed and I fear that something happened to the female when the male continued singing loudly into the third day but nest box activity ceased. It was good while it lasted.

Linking today to World Bird Wednesday.