# Recruitment of Captive‐Reared Florida Grasshopper Sparrows After Translocation: Age of Release Matters

## TL;DR

Younger birds released into the wild after being raised in captivity adapt better and breed more successfully than older birds.

## Contribution

The study shows that releasing younger birds soon after fledging improves their chances of breeding in the wild compared to older birds.

## Key findings

- Hatch-year birds had a 18% recruitment rate, while second-year birds had only 5%.
- Release age was the strongest predictor of recruitment success in logistic regression models.
- Second-year birds released close to breeding season failed to integrate into the population at similar rates to juveniles released earlier.

## Abstract

Translocation of animals raised in conservation breeding facilities is frequently used as a conservation tool, but few studies have assessed the age of release that maximizes recruitment post‐translocation. For birds, holding captive‐reared juveniles through their first winter is often believed to increase survival by sheltering them from expected high mortality in the wild. However, extended care in captivity requires time and expense and can be associated with the development of tame behaviors; those costs should be weighed against potential benefits. As part of a strategic conservation program for the endangered Florida grasshopper sparrow (
Ammodramus savannarum floridanus
), we released 265 sparrows raised under managed care into the Three Lakes Wildlife Management Area population in Florida during 2019–2021. Thirty‐two of 181 (18%) sparrows released as hatch‐years recruited (i.e., were confirmed to be paired and breeding), whereas only 4 of 84 (5%) sparrows released as second‐years recruited. Logistic regression analysis found support for release age class and mass on recruitment probability, but release age class was the only variable included in all the top three models. Based on the most‐parsimonious model, when mass was held at its mean value (16.47 g), the odds of recruitment for hatch‐year birds were 4.65 times (95% CI: 2.04, 11.75) that of second‐year birds. Despite being translocated only a few weeks before the onset of breeding, second‐year birds failed to recruit into the breeding population at rates comparable to individuals translocated 6–8 months earlier as nutritionally independent fledglings. It is unclear whether low recruitment for older sparrows was the result of higher mortality or dispersal. We discuss potential reasons why younger Florida grasshopper sparrows may be developmentally better suited to adapt to novel environments and recommend more research on the role of neuroplasticity during early learning periods and its influence on translocation outcomes.

We found that a non‐migratory passerine raised in a conservation breeding facility demonstrated higher recruitment when translocated soon after fledging than when translocated as second‐year birds after spending their first winter in captivity. Despite being translocated only a few weeks before the onset of breeding, second‐year birds failed to settle and recruit into the breeding population at rates comparable to individuals translocated 6–8 months earlier as juveniles. We discuss potential reasons why younger Florida grasshopper sparrows appeared to be developmentally better suited to adapt to novel environments and recommend more research on the role of neuroplasticity during early learning periods and its influence on translocation outcomes.