Sharp‐tailed Grouse in the Nebraska Sandhills Select Residual Cover Patches for Nest Sites

We evaluated selection and availability of residual cover (dead standing herbage) by sharptailed grouse (Tympanuchus phasianellus) at time of nest‐site selection in an intact and annually grazed grassland. We used radiotelemetry in 1988–1990 to locate 147 nests in the sandhills of Nebraska, USA, and classified 121 as initial nests and 26 as renests. We used visual obstruction readings (VOR) to measure the height and density of residual cover at nests and 373 landscape‐scale transects around leks (trap sites). We excluded 77 nests from vegetation analysis because green herbage or early livestock grazing compromised residual cover measurements. Most females selected nest sites with residual cover, mostly warm‐season grasses, taller and denser than surrounding vegetation. Visual obstruction readings at 70 nests ( avg x = 7.1 cm, SE = 0.4, range = 1.0–19.0) averaged almost twice the VOR of residual cover within 12m of nests ( avg x = 4.0 cm, SE = 0.3, range = 0.9–11.8) and almost three times the landscape VOR ( avg x = 2.5 cm, SE = 0.1, range = 0.5–7.9). As further evidence of the importance of residual cover, \u3e52% (n \u3e 37) of the females (initial nests) in 1988 and 1989 completed egg‐laying and were incubating before green herbage began contributing to nest cover. More than 88% (n \u3e 42) of the females relied on residual cover through egglaying in 1990 when annual drought delayed foliar development. Interested ranchers and land managers can enhance residual cover through livestock grazing management to attract females and presumably increase nest density, a key component of annual sharp‐tailed grouse productivit

Are age-related variations in breeding performance greatest when food availability is limited?

Age-related improvements in reproductive performance in seabirds have been well documented, and may be explained by improvements in foraging efficiency or increased experience and reproductive effort with age. The interactive effects of parental age and food supply on reproductive performance, however, remain poorly understood. A widespread mass mortality of pilchards Sardinops sagax in southern Australian waters in 1998 provided a unique opportunity to investigate the effects of a sudden reduction in the availability of a major prey species on Australasian gannets Morus serrator, an important local marine predator. Age-related differences in the breeding performance of gannets were evident in 1 year of reduced pilchard availability; when food was not limited, both young and experienced parents were equally capable of rearing chicks and had similar levels of breeding success. These data clearly demonstrate the interactive effects of parental age and food supply on breeding performance and suggest that such differences only become apparent when conditions become more stressful