Elizabeth A. Gow

Brood age and size influence sex-specific parental provisioning patterns in a sex-role reversed species

AbstractParents of altricial young alter provisioning effort based on offspring demand, but life-history differences between the sexes can influence the willingness of each parent to invest in a brood. Previous studies on sex-specific provisioning roles in altricial species suggest a wide range of responses by males and females, which vary depending on the life history of the species. The Northern Flicker (Colaptes auratus) is unusual among altricial birds, as it has partly reversed sex roles with males investing more in parental care than females, it has no-extra-pair young, and it engages in facultative polyandry. We investigated sex-specific provisioning patterns to see what factors (brood size, nestling age, adult age, body condition, nestling sex ratio and partner provisioning level) affected provisioning rates. Additionally, we determined nestling growth rates and estimated nestling energetic demands. Based on 232 filmed provisioning bouts at 82 nests, we found that males provisioned 1.11 times more than females. In addition, provisioning rates by males were primarily associated with nestling age, female provisioning, brood size, and body condition. Provisioning by females was more strongly related to the male’s provisioning effort and brood size. Per capita provisioning rates decreased with brood size, resulting in lighter nestlings in large broods. Our results suggest that both parents responded to the changes in brood demands, but do so governed by different factors. We suggest that the relatively high provisioning by males is related to high male assurance of paternity.ZusammenfassungAlter und Größe der Brut beeinflussen die geschlechtsspezifischen Muster des elterlichen Fütterungsaufwandes bei einer Art mit umgekehrten Geschlechterrollen Die Eltern nesthockender Jungvögel ändern ihren Fütterungsaufwand je nach Bedarf der Nachkommen, doch life history-Unterschiede zwischen den Geschlechtern können die Bereitschaft jedes Elternteils, in die Brut zu investieren, beeinflussen. Frühere Studien über geschlechtsspezifische Fütterrollen bei Arten mit nesthockenden Jungvögeln deuten darauf hin, dass es eine große Vielfalt an Antworten von Männchen und Weibchen gibt, die abhängig von der life history der Art variieren. Der Goldspecht (Colaptes auratus) ist insofern ungewöhnlich unter den Arten mit nesthockenden Jungvögeln, als er teilweise umgekehrte Geschlechterrollen hat—die Männchen investieren mehr in die Brutfürsorge als die Weibchen, es gibt keine außerhalb des Paarbundes gezeugten Jungvögel, und es tritt fakultative Polyandrie auf. Wir haben die geschlechtsspezifischen Fütterungsmuster untersucht, um zu verstehen, welche Faktoren (Brutgröße, Alter der Nestlinge, Alter der Altvögel, Körperkondition, Geschlechterverhältnis der Nestlinge und Ausmaß des Fütterungsaufwandes des Partners) die Fütterraten beeinflussten. Außerdem haben wir die Wachstumsraten der Nestlinge ermittelt und ihren Energiebedarf abgeschätzt. Auf der Grundlage von 232 gefilmten Fütterereignissen an 82 Nestern fanden wir heraus, dass Männchen 1,11 mal häufiger fütterten als Weibchen. Zudem hingen die männlichen Fütterraten hauptsächlich mit dem Alter der Nestlinge, dem Fütterungsaufwand des Weibchens, der Brutgröße und der Körperkondition zusammen. Der weibliche Fütterungsaufwand hing stärker mit dem Fütterungsaufwand des Männchens und der Brutgröße zusammen. Die Fütterraten pro Kopf nahmen mit zunehmender Brutgröße ab, was dazu führte, dass die Nestlinge in großen Bruten leichter waren. Unsere Ergebnisse deuten darauf hin, dass beide Elternteile auf die Veränderungen des Bedarfs der Brut reagierten, dabei jedoch von unterschiedlichen Faktoren beeinflusst wurden. Wir schlagen vor, dass die relativ hohen männlichen Fütterraten mit der hohen Gewissheit der Vaterschaft in Zusammenhang stehen.

Nest sanitation in response to short- and long-term changes of brood size: males clean more in a sex-role-reversed species

Nest sanitation is an understudied form of parental care that may improve offspring fitness by reducing microbes and ectoparasites in the nest. Many species clean nests, but it is unknown whether parents respond flexibly to various costs and benefits when deciding how much effort to invest. We experimentally manipulated brood size in the short term and in the long term in a cavity nester, the northern flicker, Colaptes auratus, to test whether parents alter their sanitation effort in response to brood demands. Males generally removed more faecal sacs than females at all treatments and in most cases, faecal removal rates were proportional to feeding rates in control and experimental broods. The rate of sac removal was negatively correlated with feather corticosterone in females but not in males. Males maintained higher faecal removal rates than females to enlarged broods and were more flexible than females in altering their sanitation effort relative to their feeding rate. Single males, but not females, removed fewer faecal sacs than paired males, suggesting that males reduce nest sanitation effort in times of high nestling demands if it helps maximize fledging success. Across taxa, the sex that invests the most in other forms of parental care also seems to perform more nest sanitation, and future studies should test how parents value it differently depending on brood demands and intrinsic factors.

Males migrate farther than females in a differential migrant: an examination of the fasting endurance hypothesis

Patterns of migration including connectivity between breeding and non-breeding populations and intraspecific variation in the distance travelled are important to study because they can affect individual fitness and population dynamics. Using data from 182 band recoveries across North America and 17 light-level geolocators, we examined the migration patterns of the northern flicker (Colaptes auratus), a migratory woodpecker. This species is unusual among birds because males invest more in parental care than females. Breeding latitude was positively correlated to migration distance because populations in the north appeared to travel farther distances than southern populations to find wintering locations with little snow cover. Connectivity was strong for populations west and east of the Continental Divide. Contrary to the three main hypotheses for intraspecific variation in migration distance, females wintered, on average, farther north than males, although there was overlap throughout their non-breeding range. This pattern contradicts those of other species found to date and is most consistent with the fasting endurance hypothesis if investment in parental care depletes the energy reserves of male flickers more than females. We thus propose a new factor, parental effort, which may influence optimal wintering areas and migration strategies within birds, and encourage future experimental studies to test the relationship between parental care roles and migration strategies of the sexes.

Choice of Foraging Habitat by Northern Flickers Reflects Changes in Availability of their Ant Prey Linked To Ambient Temperature1

Abstract Foraging theory suggests animals should prefer habitats with a greater density of prey, but few have investigated whether birds change foraging habitats according to short-term changes in prey abundance caused by weather. We studied a woodpecker, the northern flicker (Colaptes auratus), in which the diet is composed mainly of ants collected on the ground surface. We measured the surface density of the ant prey in 1-m2 quadrats placed in 2 habitat types that had different thermal properties: open grassland and forest. The density of ants varied according to year of the study, habitat type, date during the summer, and time of day and was strongly associated with ambient temperature. In the shaded forest habitat, ant density increased linearly with air temperatures between 6 and 28 °C In contrast, the surface activity of ants in the open habitat exposed to sun began to decline once ground surface temperatures reached 26 °C Ant densities were higher in the open habitat than in the shade in relatively cold conditions but were higher in the shaded forest habitat when it was hot. Using radio telemetry, we recorded the habitat use of foraging flickers and found they shifted from foraging in the open when it was cold to foraging in shaded habitats when it was hot. Flickers tracked the density of their main prey on fine spatial and short temporal scales consistent with foraging theory.