Little Blue Heron (Egretta Caerulea), Tortuguero National Park, Limon Province, Costa Rica, Central America

Immature little blue heron (Egretta caerulea), Everglades National Park, Florida, United States of America, North America

Little Blue Heron, Egretta caerulea, wading bird standing on one foot on a pole at Captiva Island, Florida, USA

Little Blue Heron, Egretta caerulea, on tree branch in the Florida Everglades, United States of America

Common Green Tree Frog (Litoria caerulea), rainforest, Iron Range National Park, Cape York Peninsula, northern Queensland, Australia

Common Green Tree Frog (Litoria caerulea), rainforest, Iron Range National Park, Cape York Peninsula, northern Queensland, Australia

Flower, Blue Lotus (Nymphaea caerulea), Botanical Garden Berlin, Berlin, Germany, Europe

Flower, Blue Lotus (Nymphaea caerulea), Botanical Garden Berlin, Berlin, Germany, Europe

Blue Tit (Parus caerulea), Emsland, Lower Saxony, Germany, Europe

Blue Grosbeak (Guiraca caerulea), female on huisache tree, Starr County, Rio Grande Valley, South Texas, USA

passion flower, detail of blossom (Passiflora caerulea)

Little blue heron (Egretta caerulea), Africa

passion flower blooming

Search for a Blue Petrel (Halobaena caerulea) in a burrow that has been monitored for several years or even decades on ile Verte. Gulf of Morbihan, Kerguelen archipelago.

Precise measurement of the leg length of a Blue Petrel (Halobaena caerulea) after banding, as part of an annual monitoring program over several decades on ile Verte. Gulf of Morbihan, Kerguelen archipelago.

The two ornithologists take the Blue Petrels (Halobaena caerulea) being monitored from their burrows, then release them there after carrying out the required measurements. Gulf of Morbihan, Mayes Island, Kerguelen archipelago.

Reading the ring. The ornithologist delicately places a ring on the leg of the Blue Petrel (Halobaena caerulea). Gulf of Morbihan, Mayes Island, Kerguelen archipelago.

Measuring the wing of a Blue Petrel (Halobaena Caerulea). Mayes Island, Gulf of Morbihan. Kerguelen Archipelago.

Couple of Imperial Shrimp (Periclimenes imperator) on a blue sea cucumber (Actinopyga caerulea) 76 meters deep, Mayotte

Imperial Shrimp (Periclimenes imperator) on a blue sea cucumber (Actinopyga caerulea) 76 meters deep, Mayotte

Catananche caerulea 'Major'

Catananche caerulea 'Major'