Species of the day: Blue Tit

By James Duncan

Learning and Engagement Officer

With vividly bright plumage and a personable nature, the tiny Blue Tit (Parus caeruleus) is one of our most recognisable garden birds. A widely spread population of approximately 3.5 million pairs typically swells during winter, owing to the movement of substantial numbers from mainland Europe. This is most often the result of food shortages and it's during this time that almost all British gardens are likely to receive a visit from them. Despite being so eminently familiar, perhaps it's easy to forget that the Blue Tit is one of our most stunning birds. It's positively exotic and if it were rarer there's little doubt people would travel a great distance to see one. With a striking yellow breast, dazzling white cheeks, a black 'bandit' mask, multi-coloured wings and a smart blue cap, it's surely our most attractive garden resident. But, there's something distinctly fascinating about the plumage, and that is the colour blue itself. The Blue Tit is the only tit to display blue plumage, though paradoxically it doesn't have any blue feathers at all, an interesting thought when observing one in your garden. Blue isn't just unusual, it's the rarest occurring colour pigment in nature. The blue of the Blue Tit is created entirely by the way light interacts with keratin in the feathers, not by pigment contained within them. The blues we see are what's known as 'schemochromes,' colourless, submicroscopic structures that create colour purely through the way in which they reflect light back to us.   

A characteristic that makes the blue tit ever popular is of course its predilection towards using our nest boxes. Providing both supplementary nest sites and garden feeding undoubtedly plays a role in assisting blue tit survival and in the UK there's a huge industry centred around it. However, they're not afraid to be creative when nesting and may attempt it practically anywhere, often in entirely unsuitable spots. Blue Tit young require caterpillars and other invertebrates during spring, so it's possible urban birds may be at a disadvantage compared to those in favoured rural locations (such as deciduous woodland), where there's a greater abundance of fat-rich prey. As a whole they'll happily substitute their usual diet with our garden offerings and can typically be watched dangling acrobatically on a tree branch or feeder, their diagnostic jingly "si-si-siuurrrrr" ringing out across the garden. Though not dissimilar, the males often have brighter and more resplendent plumage, though this can be difficult to ascertain when observing them. 

Blue Tits may begin the hunt for a nest site during the very coldest months, though it's typically not until late March that construction commences. Like other members of their family, they'll utilise a number of soft materials to line the nest, such as moss, hair and feathers, cleverly weaving in spider silk to bind things together and herbs (such as lavender) as a natural disinfectant. The labour is carried out by the female, though the male will try his very best to ensure she isn't seduced by a rival during this time. This doesn't necessarily seem to work as polygamy is commonplace, and up to half of all Blue Tit nests may contain a hatchling that's reared by a male that is unrelated. Strategically, small passerine birds such as the Blue Tit lay large clutches of eggs to account for significant annual losses. What's particularly unusual about the Blue Tit is it very rarely has a second brood - average clutch size is eight to ten, though double this has been recorded. Once the chicks hatch, a furious frenzy of activity commences as both male and female race to feed the ravenous offspring. Life for the adults is non-stop, flitting tirelessly and energetically around the garden - it's worth a thought that they may need to catch in excess of ten thousand insects within three weeks so as to rear their brood successfully.

Blue Tit - fledgling © James Duncan