Collection and analysis of demographic data play a critical role in monitoring and management of endangered taxa. I analyzed long-term clutch size and fledgling productivity data for California least tern (Sternula antillarum browni), a federally endangered subspecies that has recently become a candidate for down-listing. While the breeding population grew from approximately 1,253 to 7,241 pair...

Nest size or nest-building activity has recently been hypothesized to be a postmating sexually selected signal in monogamous birds: females may assess a male’s parental quality and willingness to invest in reproduction by his participation in nest building. Females may thus adjust their reproductive effort (i.e. clutch size) not only to their own abilities but also to those of their mates. We i...

Understanding the size of clutches produced by only one parent may require a game-theoretic approach: clutch size may affect offspring fitness in terms of future competitive ability. If larger clutches generate smaller offspring and larger adults are more successful in acquiring and retaining resources, clutch size optima should be reduced when the probability of future competitive encounters i...

Since David Lack first proposed that birds rear as many young as they can nourish, food limitation has been accepted as the primary explanation for variation in clutch size and other life-history traits in birds. The importance of food limitation in life-history variation, however, was recently questioned on theoretical grounds. Here, we show that clutch size differences between two populations...

Female hymenoptera are renowned for their ability to adjust offspring sex ratio to local mate competition. When two females share a patch, they frequently produce clutches that differ in size, the female with the larger clutch optimally producing a more female-biased sex ratio and vice versa. Females can base their sex allocation on their own clutch size only ("self-knowledge") or on both femal...

In many cooperatively breeding animals, offspring produced earlier in life assist their parents in raising subsequent broods. Such helping behaviour is often confined to offspring of one sex. Sex-allocation theory predicts that parents overproduce offspring of the helping sex, but the expected degree of sex-ratio bias was thought to depend on specific details of female and male life histories, ...

Across North America, tree swallows have advanced their mean date of clutch initiation (lay date) by approximately 9 days over the past 30 years, apparently in response to climate change. In a sample of 2,881 nest records collected by the lay public from 1959 to 1991, we examined whether clutch size has also responded to climate change. We found that clutch size is strongly related to lay date,...

Apparent changes in breeding performance with age measured at the population level can be due to changes in individual capacity at different ages, or to the differential survival of individuals with different capabilities. Estimating the relative importance of the two is important for understanding ageing patterns in natural populations, but there are few studies of such populations in which th...

Organisms exhibit plasticity in response to their environment, but there is large variation even within populations in the expression and magnitude of response. Maternal influence alters offspring survival through size advantages in growth and development. However, the relationship between maternal influence and variation in plasticity in response to predation risk is unknown. We hypothesized t...

Grassland songbird populations across North America have experienced dramatic population declines due to habitat loss and degradation. In Canada, energy development continues to fragment and disturb prairie habitat, but effects of oil and gas development on reproductive success of songbirds in North American mixed-grass prairies remains largely unknown. From 2010-2012, in southeastern Alberta, ...