Variable drivers of primary versus secondary nesting; density‐dependence and drought effects on greater sage‐grouse

Abstract

Organisms seek to maximize fitness by balancing reproductive allocations against mortality risk, given selection pressures inherent to the environment. However, environmental conditions are often dynamic and unpredictable, which complicates the ability to achieve such a balance, and may require reproductive adjustments depending on prevailing conditions. We evaluated the effects of density‐dependent, density‐independent (drought), and individual (age, body condition) factors on nesting decisions of female greater sage‐grouse in the American Great Basin. We obtained relocations and recorded reproductive histories from 287 radio‐marked females over a period of 10 yr, and applied these data to a multi‐state model that estimated probabilities of initiating a first nest (primary nesting rate) or a second nest, given loss of a first (secondary nesting rate). This approach allowed us to evaluate the relative association between nesting rates and covariates while accounting for imperfect detection of nests. Sage‐grouse primary and secondary nesting were influenced differently by density dependence and drought. Primary nesting was high and relatively constant among years despite variable drought conditions, but was negatively associated with population size (density dependence). Secondary nesting was lower and more variable compared to primary nesting, was similarly influenced by density‐dependence, and was also sensitive to drought conditions. Females known to initiate second nests were in better body condition than females that only initiated first nests, and females of intermediate age had higher primary nesting rates, whereas secondary nesting was unaffected by age. Our results suggest that females were more flexible and responded more readily to changing conditions when allocating resources to second nests. These results are consistent with patterns that have been demonstrated for female allocation to clutch size in this system, and suggest that when conditions are poor second nests reflect a tipping point where reproductive costs (increased mortality) outweigh benefits (offspring reproductive value).

Senescence and carryover effects of reproductive performance influence migration, condition, and breeding propensity in a small shorebird

“…It is possible that the patterns we saw in breeding propensity, condition, and migration timing were related to population density rather than individual carryover effects (Blomberg et al., ; Gill et al., ; Stokke, Moller, Saether, Rheinwald, & Gutscher, ). Seasonal compensation effects act through changes in population size that affect subsequent periods through density dependence.…”

“…As organisms age, their reproductive costs may increase (Proaktor, Milner‐Gulland, & Coulson, ), and their survival prospects may decrease (Nussey, Froy, Lemaitre, Gaillard, & Austad, ), and thus the optimal decision to breed or not also should change through time. In addition to these intrinsic changes in potential fitness, studies of breeding propensity have found that extrinsic factors such as food availability, population density, and predation threat also have an effect on breeding propensity (Blomberg, Gibson, Atamian, & Sedinger, ; Hoy, Millon, Petty, Whitfield, & Lambin, ; Reed, Gauthier, & Giroux, ; Sedinger et al., ).…”

Fitness landscapes and life‐table response experiments predict the importance of local areas to population dynamics

“…). We calculated female success (FS), the probability that a female successfully hatched at least one clutch of eggs, using the following equation: where NS represented nest success previously calculated using the habitat variables described above, breeding probability (0.85) was the probability a female initiated a clutch, and renesting probability (0.385) represented the mean probability of a second nesting attempt by females after a first unsuccessful attempt (Blomberg et al., in press).…”

“… Vital rates used to calculate fecundity in the matrix were female breeding propensity (juvenile = 0.7765 and adult = 0.8507; Blomberg et al., in press), renesting probability, and age‐specific clutch size (juvenile = 3.6 and adult = 3.95; Atamian and Sedinger , Blomberg et al. ), post‐fledging survival (0.528; Blomberg et al.…”

Direct and indirect effects of nesting density on survival and breeding propensity of an endangered shorebird

“…We used data from a 10-yr study of plover demography to address these objectives. As the size of breeding populations increases, individuals can compress territories (Severinghaus 1996), move to subpar habitat where survival and reproduction are relatively low (Gill et al 2001), or skip breeding (e.g., Sedinger et al 2001, Reed et al 2004, Hoy et al 2016, Blomberg et al 2017. The implicit assumption is that territoriality will limit population sizes either directly or indirectly (Brown 1969).…”