Evidence of nest abandonment in Grass Wrens Cistothorus platensis suggests that non-breeding nests are not structures that differ in function from breeding nests

LLAMBÍAS, PAULO EMILIO; JEFFERIES, MARÍA MILAGROS; ZARCO, AGUSTÍN; GARRIDO CORIA, PAULA SABRINA; ARRIETA, RAMIRO SANTIAGO

Journal für Ornithologie

Springer

Año: 2022

2193-7192

Several hypotheses propose an adaptive function of non-breeding nests (femaleattraction, decoys for nest predators and safe places for roosting). Alternatively, nonbreedingnests may be structures abandoned before completion. Grass WrensCistothorus platensis build two types of non-breeding nests: platform and dummynests. Platforms are rudimentary accumulations of grasses whilst dummies are domeshaped,similar in appearance to breeding nests. We assess nest ontogeny, structure,dimensions and placement of non-breeding and breeding nests to provide evidence of abandonment. We predict that non-breeding nests would lack several of the nestlayers present in breeding nests but would not differ in nesting microhabitat. Platformshad an incomplete structural layer and lacked most of the functional layers present inthe breeding nests. Dummy nests had a complete structural layer, but often lackedsome of the layers (lining and nest cup) that were added during the later stages ofbuilding. Breeding and non-breeding nests did not differ in seven nesting microhabitatvariables. These results are in line with the hypothesis that platforms and dummy nestsare structures abandoned during the building process. Differences between nonbreedingand breeding nests in both nest and entrance orientation suggest that nestswith an NNE orientation were less likely to be abandoned. Hence, wrens may abandonnests if they perceive unsuitable ambient conditions at the nest site. However, othercauses of desertion such as the encounter of a predator during building were notevaluated. The study of non-breeding nests may provide the opportunity to evaluatethe costs and benefits of nest desertion as well as insights in how function can shapenest architecture and location