Nests are built by animals from a variety of taxa, and serve as receptacles
for eggs and developing offspring. Where nests are built solely or mainly
by one sex, they also have the potential to serve as extended ornaments, be
cause aspects of construction potentially reveal or amplify characteristics
of the builder to prospective mates. Here, we develop novel indices to qua
ntify nest structure and examine variation in temporal and structural aspec
ts of nest construction in relation to morphological, immunological, and ph
ysiological traits in male three-spined sticklebacks, Gasterosteus aculeatu
s. Wild-caught male sticklebacks that began construction within 3 days of b
eing transferred to the laboratory built "neater" nests than fish that took
longer to start, and we present alternative testable hypotheses that could
explain this pattern. Various characteristics of nest-building males corre
lated with nest structure. The relative weight of the building male's kidne
y-which secretes a glue-like protein used in nest building and whose develo
pment is androgen-dependent-correlated positively with nest "neatness." We
also found males with enlarged spleens tan indicator of immune stress) to c
onstruct less "compact" nests. The structure of a nest may therefore be imp
ortant not only in determining its functional capacity, but may also act as
a quality-revealing ornament. We suggest that females may gain valuable in
formation regarding male health status and androgen levels from nest inspec
tion.