The animal on the cover of Interactive Data Visualization for the Web is a long-tail tit or bushtit (Aegithalos caudatus). The bushtit is a common species of bird found throughout Europe and Asia. The caudatus group of the species has a pure white head.
These birds are known for their tiny size, measuring at around only 13-15 cm in length, including their tail. The long-tail tit is recognized by its stubby bill, contrasted to its long, narrow tail. Females and males are indistinguishable, both undergoing a full moult before their first winter. Their adult plumage is primarily black and white with accents of grey and pink.
The bushtit inhabits deciduous and mixed woodland, feeding on insects with a preference for eggs and larvae of moths and butterflies, and favoring oak, ash, and sycamore trees. They tend to nest in scrub areas usually closer to the ground.
The cover image is from a loose plate of Hungarian origin. The cover font is Adobe ITC Garamond. The text font is Adobe Minion Pro; the heading font is Adobe Myriad Condensed; and the code font is Dalton Maag’s Ubuntu Mono.