Dl. Stokes et Pd. Boersma, NEST-SITE CHARACTERISTICS AND REPRODUCTIVE SUCCESS IN MAGELLANIC PENGUINS (SPHENISCUS-MAGELLANICUS), The Auk, 115(1), 1998, pp. 34-49
We used cross-sectional, longitudinal, and experimental data to invest
igate the effects of habitat at the smallest spatial scale-the nest si
te-on reproductive success of Magellanic Penguins (Spheniscus magellan
icus). Over an eight-year period, the amount of nest cover was positiv
ely correlated with fledging success. The same pairs tended to be more
successful when they had more nest cover, and experimental increases
and decreases in cover significantly affected survival of nest content
s. Other characteristics of nest sites, such as nest type and type of
vegetation over the nest, did not affect success. The positive effect
of cover resulted mainly from reduced exposure of nest contents to pre
dators during incubation and to high temperatures when chicks were you
ng. Roof cover was positively correlated with fledging success in nest
s from all areas. Cover on the sides of the nest giving the most prote
ction from the sun was positively correlated with fledging success in
warmer sites and with survival of young chicks in all areas. Young chi
cks at nests with less cover were more likely to move from their nests
and to die on hot days. Experimental results indicated that the likel
ihood of egg detection bq predators decreased with increasing nest cov
er Height of nest entrance was a significant predictor of egg loss, su
ggesting that accessibility of nest contents to predators was an impor
tant component of predation risk. Thermal properties of nests and risk
of predation were related; predation of nest contents was more likely
when adults were absent, and during hot weather adults were more ofte
n absent from nests with little cover. Although the effect of cover on
success was small relative to the large yearly variation in success d
ue to food conditions, cover is likely to influence lifetime reproduct
ive success substantially. Large and long-term data sets and experimen
tal approaches may be necessary to identify subtle but biologically im
portant factors among long-lived organisms that inhabit variable envir
onments.