Subarctic Canada Research Articles

Collapse of permafrost mounds along a subarctic river over the last 100 years (northern Québec)

Widespread permafrost decay is currently occurring in the northern hemisphere. In subarctic Québec, most permafrost mounds are located in peatlands in the form of palsas and peat plateaus. The formation and degradation of these periglacial landforms are influenced by several regional and local factors including air temperature, depth of snow cover, and peat insulation. Mineral palsas are another type of permafrost landforms found along river shores in subarctic Canada. Due to their peculiar position near or in the river floodplain, the dynamics of these palsas are influenced by water level fluctuations. This study examines palsa dynamics along a subarctic river, the Boniface River, in northern Québec. Mapping of palsas and thermokarst ponds over a 44-year period, i.e., from 1957 (from aerial photographs) to 2001 (from field surveys) was used to evaluate changes in the distribution and area covered by permafrost landforms. Also the decay of 14 palsas was assessed using the mortality dates of black spruce trees as determined by tree-ring analysis. Between 1957 and 2001 the area occupied by palsas decreased by 23% whereas 76% of the present-day thermokarst area formed since 1957. No new palsas developed during this period. For the 14 palsas studied, degradation began at the end of the 19th century and accelerated during the 20th century. Palsa degradation was closely related to distance from the river channel. Palsas located in the river floodplain were the most affected by thawing and showed a 48% reduction in area. Degradation was less severe for palsas located 1 to 15 m from the river margin, which experienced a 19% reduction in area. The spatiotemporal distribution of palsas suggests that changes in water level are among the most important factors influencing the dynamics of riparian palsas, particularly for those palsas directly in contact with the river water.

The forests and woodlands of Labrador, Canada: ecology, distribution and future management

AbstractLabrador, Canada is the last relatively undeveloped landmass of Boreal and subarctic Canada. Its land area is over 288,000 km2, with less than 1% developed, and a human population of below 30,000. Labrador is greater than 60% forest‐ and woodland‐covered and over 30% tundra, soil and rock barrens. We review the ecology and distribution of forests, woodlands, and related vegetation of Labrador within the context of climate, forest site index, landform, soils, and disturbance. Recent ecosystem management through a public planning process with emphasis on past and future comanagement and development with traditional and western scientific principles is currently underway. Plant–animal interactions, traditional uses by aboriginal groups, and early history are also reviewed.

Hydrological processes and streamflow in a lake dominated watercourse

AbstractThis paper discusses results of a nested basin study investigating run‐off responses along the watercourse in a 137 km2 subarctic Canadian Shield watershed. Catchment areas contributing surface run‐off to the basin outlet shrink after a maximum during spring snowmelt because of storage demands in headwater wetlands and lakes. This decrease is significant as summer contributing areas to the basin outlet are only 4% the size of spring melt contributing areas. This reduction in contributing area and decrease in antecedent lake levels lead to a two order of magnitude decrease in run‐off ratios from spring snowmelt to midsummer. Furthermore, the attenuating influence of lakes on the run‐off hydrograph increases the opportunity for evaporative losses, which prevents small run‐off events from maintaining a measurable flood wave through the basin. The location at which a run‐off event is interrupted in the watercourse is a function of lake size relative to upstream run‐off inputs. Run‐off is more susceptible to evaporative losses in large receiving lakes where inflow per unit area is less. These processes cause intermittent streamflow through the basin. These results have repercussions for coupled atmospheric/hydrological models whose resolution is approaching the basin scale. The incorporation of lateral transfer schemes that encompass these processes and physiographic influences on streamflow response is encouraged. Copyright © 2006 Crown in the right of Canada. Published by John Wiley & Sons, Ltd.

Abandoned Mid-Canada Radar Line sites in the Western James region of Northern Ontario, Canada: A source of organochlorines for First Nations people?

The potential exists for human exposure to polychlorinated biphenyls (PCBs) and other contaminants originating from abandoned Mid-Canada Radar Line (MCRL) sites in sub-arctic Canada. We examined patterns of differences with respect to body burden of organochlorines (lipid-adjusted) between residents of the Ontario First Nations of Fort Albany (the site of MCRL Site 050) and Kashechewan (no radar base) and Hamilton (an industrial, southern Ontario community) to assess whether the presence of Site 050 influenced organochlorine body burden with respect to the people of Fort Albany. PCBs (Aroclor 1260 and ∑14 PCBs congeners [CBs]) and DDE in the plasma of Fort Albany and Kashechewan subjects were elevated relative to Hamilton participants. PCB and DDE-plasma levels in First Nation women were of comparable magnitude to those reported for Inuit women living in the west/central Northwest Territories. Significantly lower DDE/DDT ratios observed for Fort Albany indicates exposure to higher levels of DDT compared to Kashechewan. The probable source of DDT exposure for Fort Albany people is the DDT-contaminated soil surrounding buildings of Site 050.The results of the correspondence analysis (CA) indicated that people from Hamilton had relatively higher pesticides and lower CB body burdens, while people from Fort Albany and Kashechewan exhibited relatively higher CBs and lower pesticide levels (CA-1). The separation of Fort Albany and Kashechewan from Hamilton was also clear using questionnaire data (i.e., plotting dietary principal component [PC]-1 scores against PC-2); PC-1 was correlated with the consumption of a traditional diet. Separation of Kashechewan and Albany residents occurred because the people of Kashechewan ate more traditional meats and consumed shorebirds. Only one significant relationship was found between PC analysis and contaminant loadings; PC-1 versus CA-3 for Kashechewan.The presence of Site 050 on Anderson Island appears to have influenced organochlorine body burden of the people of Fort Albany. ANCOVA results revealed that it was not activity on Anderson Island that was important, but activity on Site 050 was the influential variable. When these results are considered with the DDE/DDT ratio data and the CB 187 results (Fort Albany and Kashechewan residents differed significantly), the findings are suggestive that Site 050 did influence organochlorine body burden of people from Fort Albany.

Snowmelt contribution to discharge from a large mountainous catchment in subarctic Canada

AbstractSnowmelt is responsible for much of the annual runoff and most of the peak discharges in subarctic mountainous regions. It also provides a significant amount of freshwater inflow to the polar seas, which has implications for Arctic Ocean circulation. Owing to considerable topographic contrasts in large mountainous basins, snow accumulation and melt patterns are highly variable in time and space, but the scarcity of data in these regions prevents the patterns from being discerned. Application of a macro‐scale hydrological model (using reanalysis data from the European Centre for Medium‐Range Weather Forecasts, the National Centers for Environmental Prediction and the North American Regional Reanalysis) offers one suitable approach to estimate the magnitude and timing of snowmelt contribution to discharge from large mountainous catchments. The Liard basin, subarctic Canada, is used as an example and the SLURP (Semi‐distributed Land‐use‐based Runoff Processes) model allows hydrograph simulation for the Liard and its sub‐basins. Three sets of reanalysis temperature and precipitation data provide inputs to assess the sensitivity of model simulation. The spatial patterns of snowmelt, runoff and stream discharge for four water years were simulated. The SLURP model was found to be sensitive to a plausible range of input conditions as depicted by the three sets of reanalysis data. Despite differences in detail among the three sets of simulation results, several generalities emerged. A comparison of simulated snow cover with satellite data confirms that there are altitudinal delays in spring flow generation though latitude has no apparent influence. Runoff lags snowmelt while the catchment integrates flows of its tributaries, yet different combinations of winter snowfall and spring melt rates cause large interannual variations in snowmelt discharge. Streamflow measured and simulated at four stations along the main river permits an evaluation of runoff contribution from various sectors of the basin. The overall pattern of melt runoff generation and the modelling approach used in this investigation are applicable to other large mountainous basins in high latitudes. Copyright © 2006 John Wiley & Sons, Ltd.

Efficacy of a hydrologic model in simulating discharge from a large mountainous catchment

Summary Three sets of climatic input data from weather station observations and reanalysis products were compared for use in the simulation of streamflow for a large mountainous basin in subarctic Canada. These data sets are statistically different or show biases for most months. Yet, when they were used in conjunction with specific suites of parameters optimized for individual data sets, the hydrological model (SLURP) was able to simulate flows from these data sets which compare satisfactorily with measured discharge of the 275,000 km 2 Liard catchment. The progressive downstream change in simulated discharge was scrutinized to reveal how and why, despite using inputs that are different, the model can simulate comparable basin outflows. It was found that through the effects of overestimating or under-adjusting the flow for various sub-basins, the model can simulate discharge that matches the measured Liard flow. This compensating mechanism enhances the flexibility of the model in producing acceptable outflow for a large catchment.

Snowmelt runoff processes in a headwater lake and its catchment, subarctic Canadian Shield

AbstractDuring the snowmelt season, surface runoff into northern Canadian Shield lakes is governed by the distribution of snow and its ablation, storage in catchment slopes and valleys, and flow delivery from uplands, bottomlands and from upper lakes. For the lake studied, time lags exist between the commencement of snowmelt and the arrival of runoff to the lake, with evaporation from the uplands and bottomlands consuming some of the meltwater produced. Inflow from an upper lake is delayed. With all these inputs, the lake becomes flooded, first forming a moat, followed by an expansion of the open water areas, which are subject to evaporation loss. Lake outflow begins when water level rises above the outlet threshold. For the snowmelt season, outflow constitutes 40% of total melt and rainfall. The lake itself is a major storage that continues to maintain outflow until the lake level drops below the threshold in early summer, after which flow ceases. Snowmelt is the main period when runoff is generated from the headwater catchment to replenish storage depleted in the previous summer, and to produce flow along the Shield valley that contains a chain of lakes. Copyright © 2006 John Wiley & Sons, Ltd.

Hydrology of subarctic Canadian Shield: heterogeneous headwater basins

A field study near Yellowknife, Northwest Territories, was conducted to understand and conceptualize better the runoff generation processes of Canadian Shield headwater basins. Results indicate that these basins can be viewed as a number of hydrological elements, defined as physiographic units, with behaviours, defined by the pattern of their functions over time, which are similar within their boundaries and dissimilar with areas adjacent. A key finding of this study is that available storage at any location is dictated by hydrological processes within the individual elements as well as inputs from adjacent elements. Runoff from an element is generated only when its saturation threshold is exceeded. The importance of inputs from adjacent elements in addressing storage demands causes their geometry and topology on the landscape to control where, when and how runoff is generated. The physical manifestation of these processes is a cascading runoff pattern through the headwater basins as their downstream locations saturate and generate runoff. The element threshold concept is proposed as the hydrological framework encompassing these processes and patterns that prevail in the shield environment.

Autumn synoptic conditions and rainfall in the subarctic Canadian Shield of the Northwest Territories, Canada

Autumn precipitation is important to the annual water budget and spring streamflow magnitude in the subarctic Canadian Shield portion of the Mackenzie Basin in northwestern Canada. The objective of this study is to improve understanding of the synoptic mechanisms generating this autumn precipitation by investigating a wet (1998) and a dry (1999) autumn over a portion of this region north of Great Slave Lake. Seven synoptic map patterns were identified using a hybrid manual–revised Kirchhofer correlation methodology. Cyclones were found to be the most important map pattern providing autumn rainfall. These cyclones tend to occur 2 to 3 days following the presence of a low in the Gulf of Alaska near the Aleutian Islands. The results of this study corroborate past research that shows Pacific atmospheric moisture transported inland provides the source for much of the cyclonic rainfall in the Mackenzie Basin. Aleutian lows, which encourage this transportation, were as common in 1998 as in 1999, but the mechanisms necessary to transfer moisture to the North Great Slave region were more entrenched in 1998 than in 1999. Winds along storm tracks through the region were weaker and more dispersed in 1999. In addition, conditions for cyclogenesis in the region were less favourable in 1999. Copyright © 2005 Royal Meteorological Society

Silot'ine: An Insurance Perspective on Northern Dene Kinship Networks in Recent History

Fundamental patterns in residential groupings, marriage, kinship networks, and alliances are examined for Dene, or Chipewyan, Indian families who occupied winter staging and outpost communities during the 1920s to 1950s, the last decades that seasonal family nomadism and fur hunting were integrally linked as part of a bush economy in central subarctic Canada. Continuities and changes in these patterns are followed into the 1960s to 1990s, an era of accelerating settlement nucleation, service centralization, and wage labor. The role and meaning of personal bilateral kindreds (silot'ine) in these varying historical contexts are highlighted in this analysis. In turn, the Chipewyan experience is used to interpret the kindred in terms of risk-management, insurance, and related theoretical perspectives. Information derives from integrated ethnographic, ethnoarchaeological, and archival research conducted among the Keysehot'ine group of southern Chipewyan between the 1970s and 1990s.

Hydrology of subarctic Canadian shield: soil-filled valleys

The Canadian Shield landscape includes bedrock uplands and valleys infilled with soil. A site near Yellowknife in subarctic Canada was studied to elucidate the hydrological behaviour of soil-filled valleys. A suite of hydrological processes was found to be important in the studied valley, including snowmelt and rainfall, ground frost development, evaporation, infiltration, lateral inflow from adjacent uplands, and surface and subsurface flows. Valley storage requirements during snowmelt are met by local meltwater infiltration, but lateral inflows in the summer are needed to satisfy the storage before runoff can be generated from the valley. The valleys perform three functions of collecting vertical and lateral water inputs, retaining and losing the water held in storage, and transferring water down the valley and generating local outflow. Unlike channel flows in humid areas, runoff from the upper valley has to meet the storage demands of the lower valley segments, often causing seepage loss along flow paths to render the flows intermittent. A fill-and-spill runoff system is proposed in which the valley physiography results in a series of segments with varying storage conditions. As water is supplied to the valley, each segment has to be filled until its storage threshold for runoff is exceeded. Then, subsurface or surface flows will be generated, but these flows may be arrested to furnish water to satisfy the storage requirements of the segments downstream. Such a flow system applies also to other valleys in the Shield environment.

Ecology and spatial distributions of surface-sediment diatoms from 77 lakes in the subarctic Canadian treeline region

Diatom ecology and species compositional patterns across current arctic treeline can provide important paleoecological information associated with climatic and environmental change. In this paper we examine the relationships between measured environmental variables and modern diatom assemblage composition from 77 lakes across the treeline ecozones of the Central Canadian Arctic. The weighted-average optima for selected environmental variables were calculated for 74 of the most common diatoms, and photographic plates of these taxa are included. Our results indicated that both forest-tundra and arctic tundra lakes differed significantly in diatom assemblage composition from boreal forest lakes. In general, planktonic diatom taxa (e.g., Cyclotella species) were more common in forested lakes, which may be due to ecological conditions related to climate. Small, benthic, alkaliphilic Fragilaria taxa reached their highest abundances in forested lakes, likely because of the more alkaline nature of these lakes. Arctic tundra lakes were characterized by higher abundances of circumneutral to acidophilic taxa. Heavily silicified Aulacoseira taxa (e.g., Aulacoseira lirata, Aulacoseira perglabra) were more common in deeper tundra lakes, likely because of the less alkaline nature of these lakes and greater wind-induced turbulence in this zone. These trends provide important information on the variability of aquatic ecosystems across this climatically sensitive vegetational gradient.Key words: arctic treeline, Canada, diatoms, paleolimnology, weighted-average optima, climate change.

Transferability of hydrological model parameters between basins in data-sparse areas, subarctic Canada

Hydrological models used for the simulation of runoff are often calibrated only on the basis of data obtained at the catchment outlet but the parameters thus derived are then applied to the simulations for the subbasins. Such a practice is common for the data-sparse areas such as the subarctic. However, it may yield erroneous results when the calibrated model parameters are applied to basins of various sizes, or with divergent physical characteristics. This study assesses the feasibility of transferring parameter estimates derived for one basin of a particular size to other basins of different dimensions, using the SLURP model for simulation and the Liard and two of its subbasins as an example. Results indicate that other than the snowmelt factor, the parameter values obtained from the subbasins are similar, but values of several parameters (e.g. maximum capacity of the soil water and groundwater storage, and snowmelt factor) are different from those derived for the large basin. Compared with applying the Liard basin parameters, the subbasins parameter sets generate higher evapotranspiration, earlier termination of the snowmelt period, more soil water storage, a shorter period with significant soil water storage and a better overall agreement between the observed and simulated runoff. It is recommended that adequate attention be given to the transferability of the parameter values to improve the simulation of subbasins hydrology.

Hydrology of subarctic Canadian shield: bedrock upland

Runoff generation processes in the Canadian Shield were investigated to reconcile the considerable variability of runoff ratios noted by previous studies. Four bedrock plots near Yellowknife, Northwest Territories, Canada were studied between May 1999 and September 2000. Surface runoff increases with rainfall and snowmelt intensity because higher values of the latter can exceed fracture infiltration capacities. The size distribution of fractures affects infiltration while the fracture network controls the direction of surface flow. Frost has no effect on infiltration since the fractures are seldom ice filled. Storms of long duration and intermittent rainfall provide intervals between rainfalls during which evaporation can reduce the water available to runoff. Available storage in bedrock depressions, both empty and soil filled, retard surface flow and lengthen residence time, in turn enhancing evaporation and infiltration at the expense of runoff. The further downslope available storage is on the slope the more control it has on plot runoff magnitude. These field results show that rainfall–runoff relationships for bedrock slopes in the Canadian Shield should be considered in terms of microtopography, bedrock and soil characteristics and climate.

Areal distribution of sulphur and oxygen isotopes in sulphate of rain over eastern North America

Three summer rainfall events were sampled simultaneously across a network of 24 stations extending from the Mississippi River to the Atlantic seaboard and from the Gulf of Mexico to subarctic Canada. The chemical and isotopic compositions of the rain and its dissolved sulphate were measured on each sample. Each event was characterized by a different air mass back trajectory, suggesting a different source region for the transported sulphate. Two of the air masses apparently originated in northern Canada, one near Great Slave Lake and the other in arctic Canada. The third air mass originated in the Gulf of Mexico. In spite of this, sulphur isotopic composition was very homogeneous over most of the network, averaging +3.41±0.95‰, indistinguishable from the means of the individual events. This value is similar to that reported for long‐range transported sulphate reaching the coastal Atlantic site of Shelburne, Nova Scotia, and supports the existence of a continent‐wide, well‐mixed atmospheric reservoir of sulphur. No correlation was observed between percent sea spray and sulphur isotopic composition presumably because of the small (less than 10%) calculated sea salt contributions. Sulphate‐oxygen isotopic compositions varied very widely from −0.7 to 18‰. Two of the events apparently derived their sulphate through scavenging of aged sulphate aerosols. Sulphate‐oxygen isotopes for the other event were correlated with those of the associated rainwater, suggesting that sulphate from that event was oxidized within the transporting air mass, implying that sulphur was transported in the atmosphere in an isotopically exchangeable form.

Carbon accumulation in permafrost peatlands in the Northwest Territories and Nunavut, Canada

Average long-term apparent rates of carbon (C) accumulation (LARCA) were estimated for four peat cores from Arctic and Subarctic Canada. Detailed analyses of dry bulk-density and C content were used to determine variations in C accumulation rates throughout the cores. LARCA range from 12.5 to 16.5 g C m-2 yr-1 over the past 6700-10000 years. Rates are lower for the surface layers of Arctic high-centred peat polygons, at 5.3 to 7.1 g C m-2 yr-1 for the last 3500-4500 years. By comparison, the rate for the near-surface peat from a Sphagnum fuscum hummock in the high Subarctic was considerably higher, at 24.1 g C m-2 yr-1. The highest carbon accumulation rates were from core segments older than 4500 BP, which represent fen stages according to palaeoecological analysis. The average LARCA in our study are considerably lower than recent estimates of average carbon accumulation in Boreal peatlands. This difference is attributable partly to lower carbon percentages in our cores compared to the mean or estimated values of 50 to 51.7% used in those studies. Another factor is the presence of ground ice, which exaggerates the apparent peat depth and leads to erroneously high values if cumulative carbon estimates are based on depth. Using cumulative dry bulk-density, as we have done, eliminates the influence of ground ice and thus makes more accurate estimates possible.

MANAGING IN THE MILLENNIUM -- TRADITIONAL ECOLOGICALKNOWLEDGE (TEK): A FIRST NATIONS APPROACH TO SUSTAINABILITY.

Academy of Management Annual Meeting Proceedings includes abstracts of all papers and symposia presented at the annual conference, plus 6-page abridged versions of the “Best Papers” accepted for inclusion in the program (approximately 10%). Papers published in the Proceedings are abridged because presenting papers at their full length could preclude subsequent journal publication. Please contact the author(s) directly for the full papers. ArticlesMANAGING IN THE MILLENNIUM -- TRADITIONAL ECOLOGICALKNOWLEDGE (TEK): A FIRST NATIONS APPROACH TO SUSTAINABILITY.GAIL WHITEMANGAIL WHITEMANPublished Online:13 Dec 2017https://doi.org/10.5465/apbpp.1999.27628079AboutSectionsPDF/EPUB ToolsDownload CitationsAdd to favoritesTrack Citations ShareShare onFacebookTwitterLinkedInRedditEmail AbstractAs the millennium ends, ecological damage continues at an unprecedented rate and the need for sustainable management is evident. Yet managers often lack a practical template--how do they "walk the talk" of sustainability? There are not many concrete examples. However, the management practices of indigenous peoples can provide important concrete insights into the practice of sustainable management. Using ethnographic data collected on the Cree tallymen of eastern James Bay (subarctic Canada), this paper provides empirical data on a First Nations approach to sustainable management and explores "traditional ecological knowledge" (TEK) as an indigenous management system that has successfully avoided ecological collapse. Perhaps most critically, research findings indicate that a TEK-based management approach is both socially and ecologically embedded. In turn, the embeddedness of TEK gives rise to a number of key principles for sustainable management: (i) humble pragmatism, (ii) a fundamental commitment to social and ecological reciprocity, and (iii) managerial leadership is based on ecological legitimacy gained through TEK. TEK also emphasizes the need to learn how to manage sustainability from outside the organization's four walls. As the millennium draws near, traditional ecological knowledge (TEK) may provide a powerful template for a sustainable future.FiguresReferencesRelatedDetails Vol. 1999, No. 1 Permissions Metrics in the past 12 months History Published online 13 December 2017 Published in print 1 August 1999 InformationCopyright of Academy of Management Journal is the property of Academy of Management and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder’s express written permission. However, users may print, download, or email articles for individual use.KeywordsSUSTAINABLE developmentINDUSTRIAL management -- Environmental aspectsMANAGEMENT stylesTRADITIONAL ecological knowledgeSOCIOCULTURAL factorsCOMMERCIAL policy -- Environmental aspectsMANAGEMENT -- Social aspectsENVIRONMENTAL engineeringSUSTAINABLE engineeringCORPORATE environmentalismDownload PDF

Body size and age of recruitment in Snow Geese Anser c. caerulescens

'At what age to start breeding?' is a question fundamental to analysis of life histories. VVhile there has been considerable interest in the theoretical aspects of age of first breeding, comparatively little work has been done on the problems of estimating recruitment rates in wild populations. Most studies to date have relied on ad hoc methods that rely on one or more assumptions which may be generally untenable. Recently, it has been suggested that mark-recapture analysis can provide a robust, statistically formal approach for the analysis of recruitment, by using 'reverse capture-histories' to estimate the probability of entering the population over a given interval. We applied this approach to data from the arctic-breeding Lesser Snow Goose Anser c. caerulescens¸, using data from a long-term study in subarctic Canada. We tested the hypothesis that recruitment rate in this species was influenced by structural size. Since arcticnesting geese rely heavily on endogenous nutrient reserves for reproduction, structurally smaller birds may be less able to recruit at a young age than larger birds. However, despite significant long-term changes in body size, and significant annual variation in recruitment rate, we found no evidence of correspondence between the two.

Geographic Variation in Song of Gambel's White-Crowned Sparrow

AbstractWhite-crowned sparrow (Zonotrichia leucophrys) song varies geographically, often forming local 'dialects' in sedentary and short-distance migratory subspecies. In playback experiments males and females can distinguish this variation. Gambel's white-crowned sparrow (Z. L. gambelii) is a long-distance migrant that breeds across subarctic Canada and Alaska. Previous studies identified a wide degree of song variation within local populations of this subspecies. I compared songs recorded in Alaska and Churchill, Manitoba, and found significant differences in acoustic structure. As in other subspecies, the most prominent differences occurred in the terminal trill portion of the song. In a playback experiment to territorial males at Churchill, males gave equivalent strong responses to both Alaska and local gambelii song, significantly weaker responses to mountain white-crowned sparrow (Z. L. oriantha) song, and the weakest responses to heterospecific song. I describe a model of song recognition in which 'dialect recognition' is a component of species recognition. I conclude that as a consequence of differences in the timing of song learning, the subspecies of white-crowned sparrow may differ in the acoustic features that they attend to in song recognition. The diversity of song types at a local level within gambelii populations may interfere with recognizing song differences between populations.

Age‐specific patterns of reproduction in White‐tailed and Willow PtarmiganLagopus leucurusandL. lagopus

Although many studies report a difference in reproductive success between old and young birds, little is known about how, why and when productivity changes as individuals age. We examined age‐dependent reproduction in two bird species that inhabit harsh tundra environments: White‐tailed PtarmiganLagopus leucurusin alpine areas and Willow PtarmiganLagopus lagopusin subarctic Canada. We evaluated reproductive performance in the light of three hypotheses: constraint, restraint and selection. Using cross‐sectional and longitudinal data, we observed significant age effects in seven of the eight life history and behavioural traits examined for the two species. However, the pattern of age effects variedconsiderably across life history stages; younger birds generally had smaller clutches, later laying dates and poorer spring body condition, but the nesting success did not vary with age. Brood‐rearing and renesting abilities were greater for older parents. The oldest age class of White‐tailed Ptarmigan showed reproductive senescence for laying date and clutch size but fledged such a large proportion of the brood that they had the highest overall production of any class. It thus appears that parental experience can compensate for reduced physical ability to produce eggs. Annual mortality rates for breeding females were U‐shaped for White‐tailed Ptarmigan, with higher rates for young and old birds, but mortality did not change with age in Willow Ptarmigan. Overall, the two species differed in the presence of age dependence for only two traits (renesting ability and annual survival). Age‐dependent effects were generally greater for White‐tailed Ptarmigan than for Willow Ptarmigan. The patterns of mortality and fecundity we observed in ptarmigan provide general support for the constraint hypothesis of reproductive performance. By examining discrete stages of reproduction, we identified the life history stages where age effects occur and propose proximate mechanisms responsible for these effects.