Fatness, Sex and Dominance; Seasonal and Daily Body Mass Changes in Willow Tits

Koivula, Kari; Orell, Markku; Rytkönen, Seppo; Lahti, Kimmo

doi:10.2307/3677321

Cited by 51 publications

(44 citation statements)

References 31 publications

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“…Ordinal logistic analyses could not detect an effect of social rank on fat and muscle scores but, taken together, our findings nevertheless suggest that dominant birds, being structurally larger, had more fat reserves and larger muscles on average. This is consistent with previous observations of larger fat stores in dominant small passerine (Carrascal et al1998;Koivula et al 1995;Pravosudov and Lucas 2000;Verhulst and Hogstad 1996), but contrast with findings in Willow tits (Clark and Ekman 1995;Ekman and Lilliendahl 1993) and in Carolina chickadees (Pravosudov et al 2003), where the reverse pattern seems to prevail.…”

Section: Body Compositionsupporting

confidence: 89%

“…Therefore, since M sum reflects long-term cold endurance (Swanson 2001), low ranking individuals were likely as good as dominants in enduring the winter cold. Dominant individuals may use better thermal shelters at night (Koivula et al 1995), but all birds presumably face sufficiently demanding thermostatic costs to require upregulation of M sum to a level that is independent of rank.…”

Section: Metabolic Performancementioning

confidence: 99%

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Dominant black-capped chickadees pay no maintenance energy costs for their wintering status and are not better at enduring cold than subordinate individuals

2011

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Winter requires physiological adjustments in northern resident passerines. Cold acclimatization is generally associated with an increase in physiological maintenance costs, measured as basal metabolic rate (BMR), and cold endurance, reflected by summit metabolic rate (M(sum)). However, several northern species also form social groups in winter and a bird's hierarchical position may influence the size of its metabolically active organs as well as its BMR. Winter metabolic performance in these species may therefore reflect a complex set of adjustments to both seasonal climatic variations and social environment. We studied the effect of social status on parameters of cold acclimatization (body mass, size of fat reserves and pectoral muscles, BMR and M(sum)) in free-living black-capped chickadees (Poecile atricapillus). Birds that were structurally large and heavy for their body size, mostly dominant individuals, carried more fat reserves and had larger pectoral muscles. However, social status had little effect on metabolic performance in the cold. Indeed, M(sum) was independent of social rank while mass-corrected BMR was slightly lower in dominant individuals, likely due to a statistical dilution effect caused by large metabolically inactive fat reserves. BMR and M(sum), whether considered in terms of whole-animal values, corrected for body mass or body size were nevertheless correlated, suggesting a functional link between these metabolic components. Our results therefore indicate that the energy cost of social dominance is not a generalized phenomenon in small wintering birds.

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Section: Body Compositionsupporting

confidence: 89%

Section: Metabolic Performancementioning

confidence: 99%

Dominant black-capped chickadees pay no maintenance energy costs for their wintering status and are not better at enduring cold than subordinate individuals

2011

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“…Every time that we used the feeder to trap willow tits, we noted the identity of flock members. After marking, willow tits were trained to come when species-specific vocalizations were played back using a tape recorder (Koivula et al 1995;Lahti et al 1998). We removed the food from focal flocks at least 2 weeks before we started home range observation.…”

Section: Bird Observationsmentioning

confidence: 99%

Home range size of willow tits: a response to winter habitat loss

et al. 2003

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We examined the behavioral response to habitat loss and fragmentation of willow tits (Parus montanus) in winter in a mosaic forest landscape in northern Finland. We studied habitat preference, flock size and home range size of 16 flocks, half of which had their territories in forests fragmented by forestry and half in continuous forest. We predicted that birds would respond to habitat loss by enlarging their home range and/or diminishing group size. In addition, to compensate for fragmentation effects, willow tits might be expected to include more optimal habitat into their territories. Flocks included on average 3.9 birds and occupied territories of 12.6 ha. Willow tits avoided open areas (clear cuts and young sapling stands) and preferred mature forests and older sapling stands or pine bogs equally. Birds responded to habitat loss by enlarging their home ranges but not by reducing the group size. Large territories included a smaller proportion of mature forests, but the proportion of sapling and pine bog habitat did not change. Birds on territories that included a large proportion of open habitat localized their activity on several distinct habitat patches that were distributed over a wide area. We conclude that willow tits adjust territory use to compensate for the inclusion of unsuitable habitat within home ranges, and older sapling areas and pine bogs serve as surrogates for mature forests. However, birds did not enlarge the proportion of forest habitat in their territories with increasing habitat loss. Thus, our data do not suggest a strong effect of fragmentation, but imply that forestry practices reduce suitable wintering habitat and carrying capacity in the area. Thus winter habitat loss may explain the observed population decline of willow tits in Finland during recent decades.

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“…For this purpose the birds were trained to respond to a specific signal so that they came to the observer and entered the balance whenever called (see Koivula et al 1995 for a detailed description of the training procedure). By this method, a large number of birds was measured within a fixed time period without the need of a permanent feeder or recapture.…”

Section: Weighingsmentioning

confidence: 99%

Seasonality in daily body mass variation in a hoarding boreal passerine

et al. 2003

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We studied the body mass variation from autumn to winter, in a free-living population of willow tits ( Parus montanus), a food-hoarding passerine living year-round in boreal forests. Our aim was to find out whether this population exhibits 'winter fattening' as part of the annual body mass cycle. 'True winter fattening' is considered to be a strategic response to winter conditions. The strategy includes an increase in both the morning mass and the daily mass increase, as winter approaches. A multivariate approach was used to find which predictors (year, date, age, sex, body size, temperature and snow depth) explained the mass variation in birds measured twice per day. Morning mass variation was explained by sex, age, wing length and snow depth. Independently, date explained morning mass variation only in adult males. None of the predictors explained the variation observed in daily mass increase in any age or sex class. Therefore, we failed to detect winter fattening in our study population of willow tits. Response to increasing night length is not due to higher absolute intake, but to higher energy acquisition rate and decreased night-time energy consumption. The results suggest that willow tits at high latitudes manage increasing energy demands on a short-term basis and respond flexibly to changing conditions by adjusting foraging efficiency and especially night-time energy expenditure.

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Fatness, Sex and Dominance; Seasonal and Daily Body Mass Changes in Willow Tits

Cited by 51 publications

References 31 publications

Dominant black-capped chickadees pay no maintenance energy costs for their wintering status and are not better at enduring cold than subordinate individuals

Dominant black-capped chickadees pay no maintenance energy costs for their wintering status and are not better at enduring cold than subordinate individuals

Home range size of willow tits: a response to winter habitat loss

Seasonality in daily body mass variation in a hoarding boreal passerine

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