Sara M. Hiebert

Repertoire size, territory acquisition and reproductive success in the song sparrow

Abstract Song repertoire size, time to first territory acquisition, territory size, territory tenure and lifetime reproductive success were measured in males of known age in a wild, resident population of song sparrows, Melospiza melodia. One-year-old males had smaller repertoires than older males, but this apparent change in repertoire size was due to attrition of individuals with small repertoires rather than to an increase in the repertoire size of individuals with age. Males with large repertoires held territories longer and had greater annual and lifetime reproductive success than males with small repertoires. Half-hour repertoire size, which may represent an ecologically more relevant measure of repertoire size perceived by a transient listener, was also positively related to territory tenure and annual reproductive success. Thus listeners might be able to assess a singing males competitive ability without sampling the entire repertoire.

Song repertoire size predicts initial mating success in male song sparrows, Melospiza melodia

Male song sparrows sing repertoires of 4–13 distinct song types and have proved a valuable model for testing hypotheses concerning the function and evolution of song complexity. Captive female song sparrows solicit more copulations in response to playback of larger repertoires, yet it remains unclear whether male repertoire size influences female mate choice in natural situations. We used long-term data from free-living song sparrows inhabiting Mandarte Island, British Columbia, Canada, to investigate whether male song repertoire size predicted three components of reproductive performance during the first year: territory acquisition, mating success and laying date. Across males whose song was recorded, males with larger repertoires were not more likely to acquire a territory, to acquire a larger territory or to settle sooner. However, after we controlled for territory size and between-year variation in the population sex ratio, first-year males with larger repertoires were more likely to mate. This was because they were more likely to pair with newly settled females, not because they were more likely to acquire territories where older females were already resident. After we controlled for territory size and between-year variation in breeding date, newly settled females laid earlier when mated with males with larger repertoires. Together with the results of previous mate choice experiments, these patterns are consistent with the hypothesis that male song repertoire size is a sexually selected trait that influences female mate choice in song sparrows.

Fitness Correlates Of Song Repertoire Size In Free-Living Song Sparrows (Melospiza Melodia)

Models of sexual selection propose that exaggerated secondary sexual ornaments indicate a male’s own fitness and the fitness of his offspring. These hypotheses have rarely been thoroughly tested in free‐living individuals because overall fitness, as opposed to fitness components, is difficult to measure. We used 20 years of data from song sparrows (Melospiza melodia) inhabiting Mandarte Island, British Columbia, Canada, to test whether a male’s song repertoire size, a secondary sexual trait, predicted overall measures of male or offspring fitness. Males with larger song repertoires contributed more independent and recruited offspring, and independent and recruited grandoffspring, to Mandarte’s population. This was because these males lived longer and reared a greater proportion of hatched chicks to independence from parental care, not because females mated to males with larger repertoires laid or hatched more eggs. Furthermore, independent offspring of males with larger repertoires were more likely to recruit and then to leave more grandoffspring than were offspring of males with small repertoires. Although we cannot distinguish whether observed fitness variation reflected genetic or environmental effects on males or their offspring, these data suggest that female song sparrows would gain immediate and intergenerational fitness benefits by pairing with males with large song repertoires.

Torpor Bout Duration during the Hibernation Season of Two Sciurid Rodents: Interrelations with Temperature and Metabolism

Torpor bouts of mammalian hibernators are generally shorter at the beginning and end and are consistently longer during the main part of the hibernation season. Because it is not known why the duration of torpor bouts changes at the beginning and end of the hibernation season, we studied this phenomenon in two sciurid rodents: Spermophilus saturatus (200–300g) and Eutamias amoenus (45-60g). We examined the seasonal change in torpor bout duration during hibernation at a constant air temperature (Ta) of 2° C in relation to (1) the minimum body temperature (minimum Tb) to which the animals could be experimentally cooled before they maintained a constant Tb or began to arouse, (2) Ta at the time of minimum Tb (minimum Ta), and (3) oxygen consumption (V̇o2) of torpid individuals at Ta 2° C. Average duration of torpor bouts during the main part of the hibernation season was about 11 d in S. saturatus and 8–9 d in E. amoenus; in response to experimental cooling, minimum Tb of both species declined as low as −0.2° C. In early and late hibernation, when torpor bouts were short, minimum Tb, minimum Ta, and V̇o2 during torpor were higher than in the main part of the hibernation season. Regression analyses suggest that minimum Tb and minimum Ta are more strongly correlated with torpor bout duration than V̇o2 in both species.

Energy Costs and Temporal Organization of Torpor in the Rufous Hummingbird (Selasphorus rufus)

Continuous records of nighttime O₂ consumption (V̇o2) from rufous hummingbirds (Selasphorus rufus) were used to determine O₂ consumption during normothermic nighttime rest, entry into torpor, steady-state torpor, and arousal from torpor over a range of air temperatures (Ta)from −1° to 24° C. Whereas entry into torpor occurred anytime during the first 9.5 h of the 12-h night, arousals were consistently initiated within 2.5 h of the end of the night in the absence of known environmental cues. During normothermic rest, V̇o2 was inversely related to Ta over the entire temperature range. During steady-state torpor, V̇o2 reached its lowest value at a Ta of approximately 8° C (=

Nectar Feeding, Diuresis, and Electrolyte Replacement of Hummingbirds

T_{a\dot{V}o_{2}min}

SIMULATED HUMAN DIVING AND HEART RATE: MAKING THE MOST OF THE DIVING RESPONSE AS A LABORATORY EXERCISE

). The measured minimum body temperature (Tbmin) was approximately 13° C The comparatively low values of Tbmin and