Brian Bevan / Pair of Reed warblers (Acrocephalus scirpaceus) feeding young at nest, Bedfordshire, England, UK, July.

Dave Bevan / Male Great spotted woodpecker (Dendrocopos major) entering nest hole and leaving with a faecal sac, Carmarthenshire, Wales, UK, June.

Morley Read / Timelapse of a King swallowtail (Papilio thoas) butterfly caterpillar drinking water from the surface of a leaf, ), showing bird dropping camouflage, Napo Province, Ecuadorian Amazon. (non-ex)

Morley Read / King swallowtail (Papilio thoas) butterfly caterpillar, showing bird dropping camouflage, Napo Province, Ecuadorian Amazon. (non-ex)

John Chan / Female Bushtit (Psaltriparus minimus) returning to nest to feed chicks, carries away a fecal sac, Southern California, USA, April.

Dave Bevan / Female Mistle thrush (Turdus viscivorus) feeding chicks and swallowing faecal sacs, Carmarthenshire, Wales, UK, May.

Dave Bevan / Pair of Mistle thrushes (Turdus viscivorus) feeding chicks and removing faecal sacs, Carmarthenshire, Wales, UK. May.

David Perpinan / Sand martin (Riparia riparia) entering nest in sand bank and leaving with a faecal sac, Scotland, June.

Brian Bevan / Starling (Sturnus vulgaris) parent feeding young before flying away with fecal sac, Bedfordshire, UK, June.

Brian Bevan / Mistle thrush (Turdus viscivorus) flying to nest, feeding young, eating fecal sac before flying away Bedfordshire, UK, April.