Under adverse conditions, older small tree finch males (<i>Camarhynchus parvulus</i>) produce more offspring than younger males.

"CONFLICT OF INTEREST The authors declare that no competing interests exist."

"We thank David Anchundia, Luke Bonifacio, Nina Gallmetzer, Fidelino Gaona, Nicholas Heimpel, Patricio Herrera, Wilson Iñiguez, Denis Mosquera, Xavier Pilataxi, Ingrid Rabitsch Musso, Paul Schmidt Yáñez, Sophia Stankewitz, Angel Ulloa and Julia Zarfl for field assistance. We are grateful to Erwin Nemeth and Georgine Szipl for statistical advice. We thank the Charles Darwin Research Station for logistical support and the Galapagos National Park Directorate, especially Alonso Carrión, Christian Sevilla, Rafael Chango and several park rangers for their help. The study was funded by the FWF (project number P 26556‐B22 granted to Sabine Tebbich), the Ethologische Gesellschaft e.V., a focus of excellence grant to Sabine Tebbich and scholarships from the University of Vienna. Permission for this study was granted by the Galapagos National Park Directorate (yearly permits: PC‐54‐11, PC‐02‐14, PC‐04‐15, MAE‐DPNG/DGA‐2016‐0012, PC‐02‐17). This publication is contribution number 2338 of the Charles Darwin Foundation for the Galapagos Islands."