# Applying a Method to Estimate the Breeding and Non-Breeding Population Fractions of the Globally Threatened Red-Spectacled Amazon

## TL;DR

This paper introduces a method to estimate breeding and non-breeding population fractions in a threatened parrot species using age proportions and population data.

## Contribution

The novel contribution is a simple method to infer breeding and non-breeding population fractions using phenotypic differences between adults and juveniles.

## Key findings

- The global population of the red-spectacled amazon parrot is estimated at 16,000 to 20,000 individuals with 14% juveniles and 80% non-breeders.
- The method revealed an increase in breeding pairs from ~1300 to ~1700 as the population grew.
- The approach can be used for long-term monitoring of this and other species to improve conservation strategies.

## Abstract

Information on individuals from all stages of life is crucial for advancing knowledge of the ecology, evolution, and conservation of species. However, the life cycles of many species include cryptic stages that are often overlooked in population studies, such as the non-breeding fractions in bird populations. Here, we present a simple method applicable to species that show phenotypic differences between adults and juveniles. By quantifying age proportions, total population size, and productivity, we can infer the sizes of the non-breeding and breeding fractions. We applied this approach to a threatened parrot species whose global population concentrates in a small region of Southern Brazil after breeding. Our results indicate a low proportion of juveniles (14%) and a high proportion of non-breeders (80%) within the adult population, from a global population ranging between 16,000 and 20,000 individuals. This method can be applied to long-term monitoring of this and many other species, improving our understanding of their conservation challenges and informing effective management strategies.

Population size estimates are essential for investigating numerous aspects of the ecology, evolution, and conservation of wildlife. However, the life cycles of many species include cryptic life stages that are difficult to detect or sample, such as the non-breeding fractions typical of many bird populations. Quantifying the proportions of breeders and non-breeders is crucial to better assess their conservation status and population trends. We propose a simple method applicable to species that show phenotypic differences between adults and juveniles. By quantifying the proportion of ages, the size of the whole population, and its productivity, the size of the non-breeding and breeding fractions can be inferred. We applied this approach to the red-spectacled amazon, Amazona pretrei, a threatened parrot endemic to the Brazilian Atlantic Forest. The entire global population aggregates in winter in a few localities to feed on the seeds of the Parana pine Araucaria angustifolia, a critically endangered tree whose range has declined >97% due to massive exploitation. From a global population of ~16,000 individuals in 2015 and ~20,000 individuals in 2017, our methodology allowed us to estimate a low proportion of juveniles (14%) and a large proportion of non-breeders (80%) within the adult population, with narrow confidence intervals. These proportions did not change between years, but the estimated number of breeding pairs increased, from ca. 1300 to 1700 pairs, in parallel with the global population increase. Our methodology, with its possible improvements to reduce uncertainty in estimates, can be applied to the long-term monitoring of this and many other species, to better understand their conservation challenges and inform effective management strategies.