Comparison of plumage intensity in Florida grasshopper sparrows (Ammodramus savannarum floridanus) when given NEKTON-S or NEKTON-Gelb dietary supplement at White Oak Conservation, with evidence of sexual plumage variation.

Citation

Crenshaw LC, Garlinger RD, Parrot RE, and Schumann AG. 2021. Comparison of plumage intensity in Florida grasshopper sparrows (Ammodramus savannarum floridanus) when given NEKTON-S or NEKTON-Gelb dietary supplement at White Oak Conservation, with evidence of sexual plumage variation. In Brooks M, Koutsos E, and Henry B Eds. Proceedings of the Fourteenth Conference on Zoo and Wildlife Nutrition, Zoo and Wildlife Nutrition Foundation and AZA Nutrition Advisory Group, Virtual.

Abstract

The Florida grasshopper sparrow (Ammodramus savannarum floridanus) is an endangered subspecies of the grasshopper sparrow complex endemic to the dry prairies of central Florida. Since 2019, White Oak Conservation (hereafter White Oak) has joined the U.S. Fish and Wildlife Service in an ex situ captive breeding program to save this grassland subspecies and has released approximately 300 birds into the wild to date. Florida grasshopper sparrows are predominantly brown, buff, and white, although they also bear yellow lores and wrists pigmented by carotenoids. Anecdotal evidence in the last three years suggests that wild Florida grasshopper sparrows show brighter yellow hues and darker overall plumage than their captive-bred counterparts. Here, we use a captive flock of Florida grasshopper sparrows at White Oak to evaluate whether the beta-carotene enriched dietary supplement NEKTON-GELB is more effective in encouraging bright plumage than the NEKTON-S dietary supplement currently used at White Oak. Thirteen hatch-year individuals were supplemented with NEKTON-S while seven hatch-year individuals were supplemented with NEKTON-GELB from August to the following February or March at which time all birds were photographed. Each individual was evaluated in a blind one-to-one comparison to evaluate which individual possessed brighter lores. This evaluation method was repeated for wrist intensity and overall plumage darkness. The respective win-ratios for each of the three characteristics were then reassociated with the individuals and their treatments. We found that NEKTON-S individuals had significantly yellower wrists than Nekton-GELB individuals (t₁₇ = 2.11, P = 0.04), though lore intensity and overall darkness did not significantly differ. Having identified variation in lore and wrist intensity anecdotally associated with sex, we produced linear models for each characteristic utilizing sex and supplement as independent variables. Two-way ANOVAs revealed no interaction between sex and treatment nor any impact of treatment on plumage, but sex was found to significantly impact lore and wrist intensity (F₁ = 6.30, P = 0.02; F₁ = 8.26, P = 0.01). We found that males have significantly brighter lores and wrists than females, and that NEKTON-S and NEKTON-GELB do not differ significantly in encouraging intense plumage. Further research should continue the comparative study of NEKTON-S and NEKTON-GELB through the pre-basic molt to fully capture the plumage development cycle of Florida grasshopper sparrows. Additional future research should include validating the plumage differences between male and female Florida grasshopper sparrows and exploring the ecological and evolutionary source behind this variation.

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