Hundreds of species of wild-caught birds are offered for sale in the bird markets of Java and Bali, Indonesia, to meet the demand for the largely-domestic pet and songbird trade. In the past, owls were offered only in very small numbers in these bird markets but since the release of the Harry Potter series in Indonesia in the early 2000s their popularity as pets has increased. Whereas in the past owls were collective known as Burung Hantu (“Ghost birds”), in the bird markets they are now commonly referred to as Burung Harry Potter (“Harry Potter birds”). We made a retrospective quantitative assessment of the abundance of owls in the bird markets (1979–2010) and conducted 109 surveys in 20 bird markets in 2012–2016 to quantify owls in trade. In the 1980s, 1990s and early 2000s owls were rarely recorded in Indonesia's bird markets, typically one or two and up to five per survey, and frequently no owls were recorded at all. The trade was largely confined to small scops owls. In the late 2000s more species were offered for sale, including barn and bay owls, and larger owl species such as wood-owls, eagle-owls and fish-owls; typically 10 + owls were observed per survey. In recent years, the number of owl species increased even more, and on average we recorded 17 owls per survey, yielding a total of 1810 owls, and in >90% of the surveys owls were present. In the larger bird markets in Jakarta and Bandung typically 30 to 60 owls are on offer of up to 8 species at a time. The number of owls as a proportion of all birds in the markets increased from <0.06% prior to 2002 to >0.43% post 2008, suggesting a delayed Harry Potter effect. Over this period, common species have become cheaper and less common ones have become more expensive. The owls are largely, if not exclusively, wild-caught and are sold into the domestic pet market. The release of Harry Potter films and novels in Indonesia coincided with the rise of the Internet and social media and, with some delay, the emergence of pet owl interest groups on Java and Bali, thus preventing us to demonstrate a causal Harry Potter effect on the owl trade. The overall popularity of owls as pets in Indonesia has risen to such an extent that it may imperil the conservation of some of the less abundant species. Inclusion of owls on Indonesia's protected species list, alongside all diurnal raptors, may be a first step to mitigate the negative effects of this emerging trend.