Carolina Granthon, a Boise-based researcher, is using data collected over decades to determine what factors influence the success of a California condor egg, and she has found that egg size and the female’s age are key predictors of fertility. Her work at The Peregrine Fund’s World Center for Birds of Prey could significantly improve breeding programs aimed at conserving this endangered species.
The Condor Crisis and Recovery
- California condors nearly went extinct in the 1980s, with only 22 individuals remaining.
- Intensive conservation efforts, including captive breeding at The Peregrine Fund near Boise, have helped the population rebound to nearly 400 wild condors today.
- Condors reproduce slowly, laying only one egg every other year, making each egg vital for species survival1.
Researcher’s Quest: What Makes a Good Egg?
Carolina Granthon, a Ph.D. candidate at Boise State University, joined The Peregrine Fund’s research team to analyze decades of breeding data. She focused on understanding why some eggs fail to hatch despite advanced incubation technology and attentive care.
Data-Driven Insights
Granthon studied 499 condor eggs laid between 1995 and 2024 at the propagation facility. Her findings, published in Ornithological Applications (May 2026), revealed:
- Egg Size Matters: Larger eggs were significantly more likely to be fertile.
- Overall fertility rate: 78%.
- Fertility rate among the heaviest eggs: 90%.
- Female Age is Key: Egg size increased as females matured, peaking around age 10, then stabilizing through middle age.
- Other factors tested included male age, pair bonding duration, and genetic relatedness, but female age emerged as the strongest predictor1.
Implications for Conservation
- Optimizing Breeding Programs: By prioritizing breeding pairs with females in their prime reproductive years, conservationists can maximize fertility rates.
- Better Resource Allocation: Understanding egg viability helps staff focus incubation efforts on eggs with higher success potential.
- Long-Term Impact: These insights could accelerate recovery of condor populations, reducing the risk of future declines2.
Conclusion
Carolina Granthon’s research demonstrates how decades of meticulous data collection can yield actionable strategies for endangered species recovery. By linking egg size and female age to fertility, her work provides conservationists with practical tools to improve breeding outcomes and secure the future of the California condor.
