Boreal toad breeding-site occupancy fell in the Southern Rocky Mountains
The story at a glance
Researchers estimated that the mean probability of a breeding site being occupied by boreal toads alone fell by 43.24% between 2001 and 2019. The measure is a modelled occupancy probability, not a direct count of toads.12
The study also links longer active seasons with higher modelled extinction probability and projects more pond drying under future climate scenarios. Chytrid fungus is another pressure, but the evidence does not establish climate change as the decline’s sole cause.13
The story in brief
What you need to know
- The estimated mean probability of breeding-site occupancy by boreal toads alone dropped from 0.37 in 2001 to 0.21 in 2019, a decline of 43.24%. These figures describe the likelihood of occupancy, not the number of individual toads.12
- Longer active-season length was associated with higher modelled extinction probability at breeding sites. The researchers suggest that activity extending later in the season could leave toads out of step with food availability, but say further monitoring is needed to test that explanation.13
- The study’s future climate scenarios projected lower breeding occupancy and more frequent pond drying. These are model projections, not observations of future conditions or outcomes.12
- The researchers considered chytrid fungus as part of the pressures on the toads. Their estimated effect of Bd presence on breeding-toad extinction probability was weak, but the authors note limitations in the disease data.13
- The findings concern breeding-site occupancy in the Southern Rocky Mountains. The sources describe climate-related changes as additional risks within a complex set of pressures, rather than as a complete explanation for the decline.123
Conservation context
Why this matters
The results point to linked risks for a high-elevation amphibian: changes in seasonal activity and water availability may affect breeding sites, while disease is also part of the picture. Understanding how these pressures combine is important for interpreting the reported decline and future projections.13
The developing story
What happens next
Further monitoring is needed to test whether the proposed mismatch between the toads’ active season and food availability is occurring. The study also leaves open how closely future pond drying and occupancy will follow its model projections.13
Established evidence
What we know
- Breeding-site occupancy was modelled using detection data from 75 sites, with predictions made for 152 historical and current breeding sites.13
- Pond hydroperiod modelling used remotely sensed estimates of water area alongside climate data.13
- Earlier analyses had attributed much of the decline to chytrid fungus, while this study reports a weak estimated effect of Bd presence and cautions that disease data are limited.13
Open questions
What we don't know
- The relative contribution of climate-related changes, chytrid fungus and other pressures to the observed decline remains uncertain.13
- It has not been established whether longer active seasons create a mismatch with late-season food availability; the researchers say further monitoring is needed to test this possibility.13
- The study’s future scenarios do not establish how closely pond drying or breeding-site occupancy will match projected patterns.12
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