Amphibians are declining more sharply than any other vertebrate group. The reasons trace back to the specific biology that made the group successful in the first place.
Skin that breathes is skin that absorbs
Amphibians exchange gases and water through their skin, which must stay moist and permeable for the animal to function.
That same permeability means substances in the surrounding water or soil pass readily into the body. Agricultural runoff and other contaminants reach the animal directly rather than through diet.
It also ties amphibians tightly to humidity. Small changes in leaf litter moisture or in the timing of rain alter where they can survive at all.
Two life stages means two sets of requirements
Most amphibians develop in water and live as adults on land, so a population needs both habitats within reach of each other.
Losing either one ends the cycle. A pond surrounded by ploughed field is as unusable as intact forest with no water in it.
Breeding sites are often small, temporary pools that dry seasonally. These are easily drained, filled or overlooked in planning because they do not appear as permanent water.
A fungal disease spread globally through water and trade
A skin fungus that disrupts the animal's ability to regulate water and salts across the skin has spread across continents over recent decades.
Because it lives in water and can be carried by resistant host species, it reaches populations in remote highland streams that face no other visible pressure.
Some species have collapsed within a few seasons of arrival while others persist, and the difference relates to skin chemistry, temperature and behaviour rather than to protection status.
Small ranges make single events decisive
Many amphibian species occupy very small areas, sometimes a single mountain, valley or stream system, because their moisture requirements are narrow.
A species confined that tightly has no refuge from a local event. One drought, one disease arrival or one land conversion can affect the whole population.
This is also why amphibian species are still being described in numbers. Small ranges produce many distinct species, and some are found only after they are already at risk.
Detection lags behind decline
Amphibians are secretive, nocturnal and seasonally active, so absence is hard to distinguish from a quiet year without repeated surveys.
Monitoring often relies on breeding calls, which means species that call rarely or briefly are undercounted even where survey effort exists.
The consequence is that declines are frequently confirmed retrospectively, after the population has already passed the point where straightforward habitat protection would have been enough.