In rainforest, natural fires are extremely rare, and birds and other biodiversity suffer greatly when human-initiated fires occur. Burnt forest may take hundreds or possibly thousands of years to return to its original state (Chambers et al. 1998). Human activity worsens the risk of fire and its negative impacts for a variety of reasons. For example:

• fragmentation of forests increases their edge-to-area ratio, making them less humid and more susceptible to fire, while logging or mining roads allow access to areas previously protected by their remoteness
• fires from slash-and-burn cultivation often spread into areas of primary forest
• smouldering underground coal seams or layers of peat can re-ignite forest fires during the dry season, and can burn for decades as they are difficult to extinguish. In 2003, it was estimated that as many as 1,000 underground coal fires were burning in Indonesia alone (Bhattacharya 2003).

In Indonesia during 1997–1998, fires damaged or destroyed almost 50,000 km² of forest in Borneo and Sumatra (an area larger than Switzerland) (Liew et al. 1998). Although made worse by a drought induced by El Niño, these fires were caused by humans. The 1997 fires released as much carbon into the atmosphere as the total annual carbon intake of the world’s vegetation, equivalent to Europe’s current annual carbon emissions from the combustion of fossil fuels (Page et al. 2002). Research at Bukit Barisan Selatan National Park, Sumatra, showed that the density of hornbill species decreased by 28–63% in fire-damaged forest, because of the sparse canopy and scarcity of fruit (Anggraini et al. 2000), whilst breeding productivity of red-knobbed hornbills Aceros cassidix decreased in burned sites of Tangkoko Nature Reserve, resulting in a 47% decline in recruitment (Cahill and Walker 2000). Bird composition was also largely affected by fire severity, with insectivores being most negatively affected, and these changes likely due to changes in vegetation structure and type (Adeney et al. 2006).