Climate warming is affecting the phenology and life history of animals around the world. In birds, although warm winters have been shown to advance breeding dates and affect reproductive success in a diverse range of taxa, few studies document whether changes in breeding phenology are associated with variability in reproductive effort by breeders. We leveraged a 37-year dataset on the demography of Aphelocoma coerulescens (Florida Scrub-Jay) to investigate not only whether winter weather affects scrub-jay phenology and reproductive success, but also whether winter weather affects overall reproductive effort. Scrub-jays bred early but fledged fewer offspring in springs following warm winters. Surprisingly, this reduced reproductive success came at the expense of increased reproductive effort (number of nests built, number of eggs laid, and length of the breeding period across all attempts) by the breeders. Given the well-known trade-off between reproductive effort and survival, we highlight an important but typically unrecognized cost of climate warming on birds, as revealed by a long-term study of a large, well-protected population.
LAY SUMMARY
Several species are responding to warming climates by advancing or delaying their nesting phenology.
These changes may increase, decrease, or not change the reproductive success for individuals. Given that individual survival is often negatively associated with breeding effort, it is important to measure the reproductive effort invested by individuals in relation to their reproductive success to fully understand the effects of climate change.
We used a 37-year long-term dataset on the demography of the federally Threatened Aphelocoma coerulescens (Florida Scrub-Jay) to show that warm winters led to scrub-jays having advanced lay dates and lower reproductive success (number of fledglings) while simultaneously increasing reproductive effort (number of nests built, number of eggs laid, and length of breeding season).
Our research highlights a critical but seldom quantified effect of climate change on the annual reproductive effort in birds. How increased reproductive effort may affect individual survival remains to be studied.
El calentamiento climático está afectando la fenología y la historia de vida de los animales en todo el mundo. En las aves, aunque se ha demostrado que los inviernos cálidos adelantan las fechas de reproducción y afectan el éxito reproductivo en una amplia gama de taxones, pocos estudios documentan si los cambios en la fenología reproductiva están asociados con la variabilidad en el esfuerzo reproductivo por parte de los reproductores. Aprovechamos un conjunto de datos de 37 años sobre la demografía de Aphelocoma coerulescens para investigar no solo si el clima invernal afecta la fenología y el éxito reproductivo de esta especie, sino también si el clima invernal afecta el esfuerzo reproductivo general. Los individuos de A. coerulescens criaron temprano, pero emplumaron menos crías en las primaveras que siguieron a inviernos cálidos. Sorprendentemente, este éxito reproductivo reducido se dio a expensas de un mayor esfuerzo reproductivo (número de nidos construidos, número de huevos puestos y duración del período de cría en todos los intentos) por parte de los reproductores. Dada la conocida disyuntiva entre el esfuerzo reproductivo y la supervivencia, destacamos un costo importante pero típicamente no reconocido del calentamiento climático en las aves, como lo revela un estudio a largo plazo de una población grande y bien protegida.
