Condition and coalition formation by brood-rearing common eider females

Partner choice is important in nature, and partnerships or coalitionswithin which reproduction is shared are the subject of growinginterest. However, little attention has been given to questionsof which individuals are suitable partners and why. Common eider(Somateria mollissima) females sometimes pool their broods andshare brood-rearing duties, and body condition affects caredecisions. We constructed a model in which females, based ontheir body condition and the structure of the joint brood, assessthe fitness consequences of joining a coalition versus tendingfor young alone. We tested the model's predictions by comparingdata on the condition of females in enduring and transient coalitions.Our model showed that the range of acceptable brood arrays ina female coalition decreases with increasing condition of thefemale, so females tending alone should be in better conditionthan multifemale tenders. This prediction is in agreement withprevious data. The model also predicts that females in goodcondition should join coalitions with females in poor conditionand not with other females in good condition. This predictionwas also supported by data: in enduring two-female coalitions,the positive correlation between the better female's conditionand the difference in condition between the two females wasstronger than would be expected by random grouping of females.In contrast, in transient coalitions of females, this correlationdid not differ from the correlation expected under random grouping.Model assumptions seem to fit with eider natural history, andthe model may prove to be a useful way to study brood amalgamationbehavior of waterfowl in general.     

Eider females form non-kin brood-rearing coalitions

Kin selection is a powerful tool for understanding cooperation among individuals, yet its role as the sole explanation of cooperative societies has recently been challenged on empirical grounds. These studies suggest that direct benefits of cooperation are often overlooked, and that partner choice may be a widespread mechanism of cooperation. Female eider ducks (Somateria mollissima) may rear broods alone, or they may pool their broods and share brood-rearing. Females are philopatric, and it has been suggested that colonies may largely consist of related females, which could promote interactions among relatives. Alternatively, shared brood care could be random with respect to relatedness, either because brood amalgamations are accidental and nonadaptive, or through group augmentation, assuming that the fitness of all group members increases with group size. We tested these alternatives by measuring the relatedness of co-tending eider females in enduring coalitions with microsatellite markers. Females formed enduring brood-rearing coalitions with each other at random with respect to relatedness. However, based on previous data, partner choice is nonrandom and dependent on female body condition. We discuss potential mechanisms underlying eider communal brood-rearing decisions, which may be driven by the specific ecological conditions under which sociality has evolved in this species.     

Estimating survival and adoption rates of dependent juveniles

Population growth and fitness are typically most sensitive to adult survival in long‐lived species, but variation in recruitment often explains most of the variation in fitness, as past selection has canalized adult survival. Estimating juvenile survival until age of independence has proven challenging, because marking individuals in this age class may directly affect survival. For Greater Sage‐grouse, uniquely marking juveniles in the first days of life likely results in adverse effects to survival, detection of juveniles is not perfect, and females adopt juveniles from other parents. These challenges are encountered by researchers studying avian and mammalian species with similar life histories, yet methods do not exist that explicitly estimate all these components of the recruitment process. We propose a novel data collection method and demographic model to simultaneously estimate rates of detection, survival, and adoption of juvenile individuals. Using multiple cameras to film the beginning of juvenile activity on specific days, we obtained counts of juveniles associated with marked females. Increases of juveniles to broods provided information that enabled us to estimate rates of adoption that can be applied at the population level. Losses from broods informed apparent survival. These losses could be attributed to death, or they could be chicks that were adopted by other females. We found evidence that apparent survival of juveniles was influenced by localized weather patterns when chicks were young. Similarly, we found that young chicks were more susceptible to the adverse effect of attending females being flushed by an observer. Both of these patterns diminished quickly as chicks aged. We provide the first‐ever estimates of interval‐specific adoption rates. Our results suggest that researchers should be cautious when designing studies to estimate juvenile survival. More importantly, they provide insight into adoption, a behavior that has been known to exist for decades.     

The United States of the United Races: a rejoinder

I respond to a review by C. Matthew Snipp, revisiting how my book connects abolitionist leanings to acceptance of racial mixing in the Early Republic. I reiterate that, contrary to the reviewer's claims, the book does not suggest that the defence of interracial marriage has been a thriving social movement. I correct his reading of my chapter on the Civil War era, referring to both the variety of voices present, and the claims of reformers' opponents, who were the only ones who claimed racial mixing was an aim of the abolitionist movement. Lastly, I defend The United States of the United Races against Professor Snipp's characterization of it as a work anticipating a ‘post-racial’ ideal, embodied by racially mixed people, who would be the end point of the obsolescence of race as a relevant analytic tool.