Density dependence in ducks: a review of the evidence

Gunnarsson, Gunnar; Elmberg, Johan; Pöysä, Hannu; Nummi, Petri; Sjöberg, Kjell; Dessborn, Lisa; Arzel, Céline

doi:10.1007/s10344-013-0716-9

Cited by 36 publications

(35 citation statements)

References 101 publications

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“…Although density dependence affected fecundity in prairie dabbling ducks, it had both positive and negative effects that varied among species and regions, confirming that density‐dependent effects on fecundity in waterfowl depend on the life stage and spatial scale examined (Gunnarsson et al., ), similar to survival (Zhao et al., ). Density dependence is a key component of almost all population models, including continental adaptive harvest management models for waterfowl in North America (Nichols et al., ), but variation in how fecundity responds to density within a season and across a region could mask effects at larger scales.…”

Section: Discussionmentioning

confidence: 69%

Banding age ratios reveal prairie waterfowl fecundity is affected by climate, density dependence and predator–prey dynamics

Specht

Arnold

2018

Journal of Applied Ecology

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Fecundity estimates for demographic modelling are difficult to acquire at the regional spatial scales that correspond to climate shifts, land use impacts or habitat management programmes. Yet they are important for evaluating such effects. While waterfowl managers have historically used harvest‐based age ratios to assess fecundity at continental scales, widely available age ratios from late summer banding (ringing) data present an underutilized opportunity to examine a regional fecundity index with broad temporal replication. We used age ratios from banding data and hierarchical mixed‐effect models to examine how fecundity of five North American dabbling duck species was affected by temporal variation in hydrological cycles, intra‐ and interspecific density dependence and alternate prey availability, and whether those relationships were consistent across a broad geographic area. Model‐estimated fecundity was within the range of traditional harvest‐based fecundity estimates for each species. Ecological covariates explained between 16% and 53% of the temporal variation in fecundity, dependent on species. Increasing wetland inundation and an indicator of vole population irruptions were consistent predictors of increasing fecundity across all species. Species exhibited mixed positive and negative responses to interspecific and intraspecific breeding pair densities hypothesized to affect nest and brood survival respectively, highlighting the importance of integrating brood survival into fecundity metrics for precocial species. Declines in fecundity over time and across space at more northern latitudes may reflect stronger policies for grassland and wetland protection in the U.S. versus Canadian portions of the prairies over the time period of our study. Maintaining the capacity of less permanent basins to rehydrate in wetter periods through easement protection benefits fecundity, particularly for late‐nesting species that acquire a greater proportion of their reproductive energy on the breeding grounds. Synthesis and applications. Age ratios derived from postbreeding banding operations allowed us to attribute variation in waterfowl fecundity to temporal ecological variables. Effects of habitat management for waterfowl may be masked unless analysts account for this temporal variation. Postbreeding‐pulse age ratios at capture could be useful as fecundity metrics in integrated population models and for evaluating population dynamics of extensively banded nongame species, especially if adjusted for capture vulnerability using within‐season recapture data.

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Section: Discussionmentioning

confidence: 69%

Banding age ratios reveal prairie waterfowl fecundity is affected by climate, density dependence and predator–prey dynamics

Specht

Arnold

2018

Journal of Applied Ecology

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“…Taylor , Gunnarsson et al . ). Disturbance is one such modifying factor as nests may be more prone to predation when the nest is unattended.…”

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confidence: 97%

Absence from the nest due to human disturbance induces higher nest predation risk than natural recesses in Common Eiders Somateria mollissima

Stien

Ims

2015

Ibis

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Human disturbance of nesting birds may cause reduced breeding success. It is therefore necessary to assess the impact of disturbance to identify steps that minimize negative impacts. We carried out a study of nesting success at two adjacent colonies of Common Eider Somateria mollissima on the islands of Grindøya and Håkøya in northern Norway between 2006 and 2011. Over the study period, nesting success was consistently higher on Håkøya (69–82%) than on Grindøya (35–60%). Between 2009 and 2011 we used camera monitoring of individual nests to identify determinants of nest survival and predation, focusing in particular on the effect of departures from the nest due to human disturbance, which differed between the colonies due to a long‐term research project on Grindøya. Overall, absence of Common Eiders from nests due to disturbance increased the predation risk by a factor of 6.42 for an increase of one additional daily disturbance. In contrast, absence due to natural recesses did not increase nest losses. Under high levels of human disturbance, camera monitoring indicated that the main cause of breeding failure was predation, primarily by Hooded Crows Corvus cornix, but also to some extent Great Black‐backed Gulls Larus marinus. The presence of cameras did not increase the predation risk. Both the presence of researchers and the sight of Common Eider females conspicuously departing from nests are likely to have provided cues to these predators. We suggest management trials to reduce nesting disturbance through the guarding of unoccupied nests to mitigate the effects of human disturbance on reproductive success.

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“…In the Czech Republic, this finding may imply that some of the wintering sites have already reached their carrying capacity, i.e. the number of individuals in these sites is affected by density-dependent regulation (Brown 1969;Fox 2005;Gunnarsson et al 2013). Our hypothesis for the great importance of temperature-dependent wintering site conditions located on the edge of species' wintering areas was strongly supported by the preference for sites that most likely reduced winter harshness, i.e.…”

Section: Resultsmentioning

confidence: 94%

Long-term trends, total numbers and species richness of increasing waterbird populations at sites on the edge of their winter range: cold-weather refuge sites are more important than protected sites

et al. 2015

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Recent climate changes are most likely the major determining factor for the increasing importance of Central Europe for wintering waterbirds, given that most of the region is located on the edge of these species' wintering ranges. A few recent large-scale studies have demonstrated changes in species distribution at the flyway level, but detailed studies at the site level are still scarce. Using midJanuary wintering waterbird counts from 532 sites taken over a 48-year period (1966-2013), we have assessed the role of 'cold-weather refuges', i.e. sites where the selective pressures of winter harshness are reduced (e.g. sites with ample sources of running water, urban areas, warmer sites, sites with a relatively higher proportion of wetlands), and a site's protection status on species richness, total numbers and trends at the site level. We found prevailing increasing trends in total numbers and species richness at the site level, which are in line with the area's increasing importance as wintering grounds. However, some sites have likely been affected by density-dependent regulation as mean total numbers per site have not increased since the 1990s. Density dependence may also be a reflection of an increasing number of sites with running water in traditionally cold areas. Factors affecting trends in species richness at the site level are however less predictable. We demonstrate the great importance of cold-weather refuges, where running water has an effect on total numbers, species richness and trend affect total numbers, warmer areas and higher proportions of wetlands in the surroundings affect total numbers and species richness and urban areas affect total numbers. However, we found that legislative safeguards for sites, such as the establishment of Nature Reserves and Special Protection Areas, have no significant effects. Our findings therefore suggest that the effect of temperature and presence of cold-weather refuges (as defined here) are more relevant to this observed increasing trend of wintering waterbirds on the edge of wintering ranges than a reduction in human developmental pressures.

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Density dependence in ducks: a review of the evidence

Cited by 36 publications

References 101 publications

Banding age ratios reveal prairie waterfowl fecundity is affected by climate, density dependence and predator–prey dynamics

Banding age ratios reveal prairie waterfowl fecundity is affected by climate, density dependence and predator–prey dynamics

Absence from the nest due to human disturbance induces higher nest predation risk than natural recesses in Common Eiders Somateria mollissima

Long-term trends, total numbers and species richness of increasing waterbird populations at sites on the edge of their winter range: cold-weather refuge sites are more important than protected sites

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