Understanding the effects of conservation management, inbreeding and diet on reproductive fitness in a threatened bird species

Understanding the factors that influence reproductive success is crucial for effective conservation of threatened species. Inbreeding depression poses a significant threat to small populations, with its effects often varying across life stages and population contexts. Similarly, diet composition can substantially impact reproductive output, particularly in degraded habitats where natural food resources may be limited. While supplementary feeding can help overcome resource limitations, its broader effects on host and population health, including host-microbe relationships, remain poorly understood. Recent methodological advances now enable detailed examination of these factors: lethal equivalents can provide standardised measures of inbreeding effects, DNA metabarcoding can reveal unprecedented resolution of dietary patterns, stable isotope analysis can quantify supplementary food consumption at the individual level, and genome-resolved metagenomics can characterise gut microbial communities. Together, these approaches offer new opportunities to examine how genetic and dietary factors influence population recovery.

The Mauritius parakeet (Alexandrinus eques) provides an ideal study system for investigating these dynamics, having recovered from 20 individuals in the 1980s to several hundred birds across two populations (North and South) with different management intensities. Using long-term breeding data (2000-2020), we found significant inbreeding effects on hatching but not fledging success, with lethal equivalents differing between populations (North: 2.40, South: 4.39). DNA metabarcoding revealed 83 plant taxa in the diet, with higher native species richness in the North population despite historical habitat degradation. Stable isotope analysis showed that supplementary food constituted a significant portion of the diet and boosted reproductive success, though higher consumption in the North (84.2%) compared to the South (29.4%) did not translate to significantly higher reproductive success. Additionally, an endemic plant species was a significant positive predictor of reproductive success in the South, whilst supplementary food species were positive predictors in the North. Preliminary genome-resolved metagenomic analysis revealed population-specific differences in gut microbiota composition, with higher microbial diversity in the South and a potential relationship between supplementary feeding and reduced microbiome diversity.

This research reveals population-specific patterns in how dietary composition and genetic factors influence reproductive success in a threatened species. The populations showed contrasting relationships between diet and breeding output: supplementary food was crucial in the North, while endemic plant consumption was more important in the South. Despite higher lethal equivalents, the South population maintained higher reproductive success. These findings demonstrate how genetic and dietary factors can interact differently across populations, highlighting the importance of comprehensive monitoring and locally adapted conservation strategies.