Reliability of Aerial Cache Surveys to Monitor Beaver Population Trends on Prairie Rivers in Montana

Swenson, Jon E.; Knapp, Stephen J.; Martin, Peter R.; Hinz, Thomas C.

doi:10.2307/3808605

Cited by 19 publications

(19 citation statements)

References 14 publications

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“…Although the size of beaver family groups can change from year to year while caches persist (Swenson et al 1983), aerial surveys of beaver food caches provide an efficient and precise technique to detect trends in beaver populations over longer time periods that are commonly specified by monitoring programs. Many monitoring programs are designed to detect population changes within 10 years (Marsh and Trenham 2008).…”

Section: Discussionmentioning

confidence: 99%

“…Beaver food caches on the BHNF should be detectable with high probability because they are constructed in open water and are highly visible during aerial surveys. Detection probability of caches was 0.89 in forested habitats in southeastern and central Wyoming, USA using a helicopter survey (Osmundson and Buskirk 1993), and detection probability of caches during helicopter surveys was 0.89 on two prairie rivers in southeastern Montana, USA (Swenson et al 1983). Payne (1981) found helicopters to be more efficient than fixed-wing aircraft at detecting beaver lodges and caches in the boreal forest of Newfoundland, Canada (detection probability; helicopter = 0.89, fixed-wing = 0.61).…”

Section: Discussionmentioning

confidence: 99%

“…Beaver abundance and presence is monitored in selected watersheds using helicopter surveys (Beck et al 2008), which have been successfully used to monitor beaver food caches (Payne 1981;Swenson et al 1983;Smith 1999). Aerial monitoring occurs in late October and early November.…”

Section: Field Methodsmentioning

confidence: 99%

“…We thought that this assumption was appropriate because sixth-level watersheds are on average approximately 6,000 ha and often only contain one food cache. Caches are enumerated by one observer during aerial surveys, a common method for monitoring beaver populations (Swenson et al 1983). A sample of 40 watersheds was determined to be a logistically feasible sample size for each monitoring year, and these watersheds were randomly selected for monitoring beaver abundance.…”

Section: Sampling Designmentioning

confidence: 99%

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Design to monitor trend in abundance and presence of American beaver (Castor canadensis) at the national forest scale

Beck

Dauwalter

Gerow

et al. 2009

Environ Monit Assess

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Wildlife conservationists design monitoring programs to assess population dynamics, project future population states, and evaluate the impacts of management actions on populations. Because agency mandates and conservation laws call for monitoring data to elicit management responses, it is imperative to design programs that match the administrative scale for which management decisions are made. We describe a program to monitor population trends in American beaver (Castor canadensis) on the US Department of Agriculture, Black Hills National Forest (BHNF) in southwestern South Dakota and northeastern Wyoming, USA. Beaver have been designated as a management indicator species on the BHNF because of their association with riparian and aquatic habitats and its status as a keystone species. We designed our program to monitor the density of beaver food caches (abundance) within sampling units with beaver and the proportion of sampling units with beavers present at the scale of a national forest. We designated watersheds as sampling units in a stratified random sampling design that we developed based on habitat modeling results. Habitat modeling indicated that the most suitable beaver habitat was near perennial water, near aspen (Populus tremuloides) and willow (Salix spp.), and in low gradient streams at lower elevations. Results from the initial monitoring period in October 2007 allowed us to assess costs and logistical considerations, validate our habitat model, and conduct power analyses to assess whether our sampling design could detect the level of declines in beaver stated in the monitoring objectives. Beaver food caches were located in 20 of 52 sampled watersheds. Monitoring 20 to 25 watersheds with beaver should provide sufficient power to detect 15-40% declines in the beaver food cache index as well as a twofold decline in the odds of beaver being present in watersheds. Indices of abundance, such as the beaver food cache index, provide a practical measure of population status to conduct long-term monitoring across broad landscapes such as national forests.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Field Methodsmentioning

confidence: 99%

Section: Sampling Designmentioning

confidence: 99%

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Design to monitor trend in abundance and presence of American beaver (Castor canadensis) at the national forest scale

Beck

Dauwalter

Gerow

et al. 2009

Environ Monit Assess

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show abstract

“…In 1996,1998,1999,2001,2003,2005,2007, and 2009 we counted beaver colonies across the entire park using fixed-wing aircraft (Supercub PA-18) following standard methods published for aerial beaver surveys (Hay 1958, Swenson et al 1983. Our objective was a complete count of YNP.…”

Section: New Beaver Surveysmentioning

confidence: 99%

The History and Current Status and Distribution of Beavers in Yellowstone National Park

Smith

Tyers

2012

Northwest Science

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Too many to count: Using orthophotography to census an unharvested beaver (Castor canadensis) population in Ontario

et al. 2022

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Various methods exist to monitor wildlife populations and estimate trends in their distribution and abundance. For American beaver (Castor canadensis), aerial surveys provide a means to obtain abundance data over large areas and typically involve observers searching watercourses and shorelines for active beaver presence. Here, we describe a systematic aerial photographic census we designed and executed in autumn to quantify annual beaver colony abundance on the 184‐km2 Michipicoten Island, Ontario, from 2015 to 2019. Aerial photographs were stitched together into orthophotomosaics after each census and visually searched for beaver food caches, with each food cache representing an independent beaver colony. Our methods revealed that beaver colony abundance declined substantially from a peak of 6.1 colonies/km2 in 2015, the highest reported across North America, to 0.4 colonies/km2 in 2018. Beaver abundance remained low through 2019. Although photographing the entire isolated study area required relatively little time and effort, even when beaver density was very high, post‐census processing work was time‐consuming. Lessons learned will improve efficiencies of our future censuses and aid other researchers. Our method is advantageous over traditional aerial wildlife surveys in that it provides a digital and visual record that can be used for additional analyses.

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Reliability of Aerial Cache Surveys to Monitor Beaver Population Trends on Prairie Rivers in Montana

Cited by 19 publications

References 14 publications

Design to monitor trend in abundance and presence of American beaver (Castor canadensis) at the national forest scale

Design to monitor trend in abundance and presence of American beaver (Castor canadensis) at the national forest scale

The History and Current Status and Distribution of Beavers in Yellowstone National Park

Too many to count: Using orthophotography to census an unharvested beaver (Castor canadensis) population in Ontario

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