The week in wildlife

Glass frogs (Hyla punctata) are common in flooded forest. At night the back of the frog is reddish tan and the flanks and limbs are green. By day, the back of the frog is pale green with dark red flecks and a creamy yellow stripe Photograph: Jeffrey Arguedas/EPA

A plataniste or Ganges river dolphin in the Karnaphuli river, Bangladesh. Dwindling freshwater dolphin numbers are raising concerns about the declining health of some of the world’s most important rivers, shows a new study by WWF Photograph: François Xavier Pelletier/WWF-Canon WWF-Canon

A herd of cattle make their way through the floodwater to find dry land on 6 September 2010 in Wangaratta, Australia. Many parts of Victoria were devastated by flood waters when heavy winds and rain inundated the area causing the worst flooding in over a decade. The State Emergency Service has ordered the evacuation of several cities and are warning residents that the threat is not yet over Photograph: Scott Barbour/Getty Images

Scientists have found the first evidence to suggest that zooplankton, tiny creatures that inhabit the ocean in their billions, choose their sexual partners. Despite being blind, the plankton try out and reject sexual advances of others, reserving their affections for bigger mates. This means sexual selection plays a key role in plankton evolution. Details are published in the journal Oecologia. Photographer Spike Walker was awarded the Royal Photographic Society's combined Royal Colleges medal for his 'outstanding contribution to photography and its application in the service of medicine'. Photograph: Spike Walker/Wellcome Images

This is one of the 5,000-plus camera-trap images used to develop the Wildlife Picture Index, a new way to measure biodiversity across large landscapes. With a click of the camera, scientists from the Wildlife Conservation Society and Zoological Society of London have developed a new way to accurately monitor long-term trends in rare and vanishing species over large landscapes. The methodology collects images from remote "camera traps", which automatically photograph anything that lopes, waddles, or slinks past. These virtual photo albums - sometimes containing thousands of photos of dozens of species - are then run through a statistical analysis to produce metrics for diversity and distribution of a broad range of wildlife. The study appears in the August, 2010 issue of the journal Animal Conservation Photograph: WCS

The Sierra Nevada red fox was thought to be extinct until three weeks ago. US forest service biologists captured photos of the fox with a camera set up on a trail, and took DNA samples of saliva pulled from a bait bag the fox bit into Photograph: Keith Slausen/US Forest Service

A red-crowned river turtle, which was once widespread in the rivers of northern India, Bangladesh and Nepal. However, intensive egg collection, capture of adults for consumption, dams and river pollution have caused such rapid decline that one single population remains, in the Chambal river of central India Photograph: Peter Paul van Dijk/CI

A dwarf seahorse on turtle grass. One of the world's smallest seahorses faces extinction because of the BP oil spill, conservationists have warned Photograph: Robert Sisson/Getty Images

A white-tailed eagle has turned up on the seabird haven of the Farne Islands for the first time. The bird, one of a group released in eastern Scotland last month as part of a reintroduction scheme for the species, arrived on the islands on Saturday. The eagles, which are nicknamed 'flying barn doors' because of their size, were persecuted to extinction in England in the early 19th century and disappeared from Scotland in the early 20th century Photograph: National Trust/Mark Breaks/PA

A polar bear cub hides behind its mother near the Norwegian island of Spitzbergen, Svalbard archipelago in the Arctic Ocean Photograph: Paul Goldstein/Exodus Travels

This 'venue' of vultures (a group of vultures can also be called a 'committee' or a 'wake') in this image includes slender billed (left), white-rumped (m), and red-headed vultures (right), all of which have persisted in Cambodia while other vulture populations in Asia have all but vanished says a new report. Photograph: Hugh Wright

Azara's owl monkeys have switched their activity pattern from strict nocturnality to one that also includes regular daytime activity. Owl monkeys need moonlight as much as a biological clock for nocturnal activity, a new report shows. Harsher climate, food availability, and the lack of predators or diurnal competitors, have been proposed as factors favouring evolutionary switches in primate activity patterns Photograph: University of Pennsylvania

An Indian one-horned rhino grazes on a highland area as a forest guard keeps watch at the Pobitora wildlife sanctuary in north-east India. The third wave of flood has submerged more than 60% of the wildlife sanctuary and a majority of the animals have taken shelter in the highlands. According to park officials, there will be a massive habitat shortage for animals in the sanctuary this year as three consecutive floods have totally destroyed the grasslands. Pobitora has the highest density of one-horned rhino population in the world of about 84, according to 2009 census Photograph: STR/EPA

A humpback whale is caught in creel fishing buoys as it flounders in the sea off the coast of the Shetland Islands off north-east Scotland. Animal safety officials are consulting with international animal experts to find a way of rescuing the 40ft-long whale, but rough weather is making the operation more difficult Photograph: spca/AP

View of an ornamental tree leaf at the public garden in New Delhi, India. Exceptional heavy monsoon in the Indian capital has given a boost to its flora and fauna as according to the Indian Metrological Department the Indian capital experienced prolonged rainfall this season. Delhi had recorded more than 800mm of rainfall so far this monsoon, which is 43% above average Photograph: Harish Tyagi/EPA

A Grevy's zebra and its young in the wild. Conservationists are using information gathered from surveys of hundreds of people in a remote area of Kenya to find ways to help protect the endangered type of zebra Photograph: Marwell/PA

An 18-month study of remote human settlements deep in the Congolese jungle warns that chimpanzees are are being subjected to a 'wave of killing' by hunters pursuing them for bushmeat Photograph: T.C. Hicks/African Primates/IUCN

Spruce gran picea (9,500 years old; Fulufjllet, Sweden). In this TED talk titled The world's oldest living things, Rachel Sussman shows photographs of the world's oldest continuously living organisms – from 2,000-year-old brain coral off Tobago's coast to an "underground forest" in South Africa that has lived since before the dawn of agriculture Photograph: Rachel Sussman