Beaver Management Technical Paper #3 Beaver Life History and Ecology Best Science Review April 2020 Alternate Formats Available Beaver Management Technical Paper #3 Beaver Life History and Ecology Best Science Review Submitted by: Jen Vanderhoof King County Water and Land Resources Division Department of Natural Resources and Parks Beaver Life History and Ecology Best Science Review Acknowledgements Extensive review and comments were provided by Bailey Keeler on the “Diet” and “Territoriality & Scent Mounds” sections, and she wrote a portion of the “Predation” section. Review and comments were provided by Bailey Keeler, Brandon Duncan, Matt MacDonald, and Kate O’Laughlin of King County. Dawn Duddleson, librarian for Water and Land Resources Division, obtained the majority of the papers cited in this report. Tom Ventur provided technical support and formatting for this document. Citation King County. 2020. Beaver management technical paper #3: beaver life history and ecology best science review. Prepared by Jen Vanderhoof, Water and Land Resources Division. Seattle, Washington. King County Science and Technical Support Section i April 2020 Beaver Life History and Ecology Best Science Review Table of Contents 1.0 Introduction .....................................................................................................................1 2.0 Beaver Populations .........................................................................................................3 2.1 History .........................................................................................................................3 2.1.1 Historic populations and trapping ............................................................................ 3 2.1.2 Reintroduction.........................................................................................................4 2.2 Current population estimates ....................................................................................... 8 2.3 Carrying capacity .........................................................................................................9 3.0 Biology ..........................................................................................................................10 3.1 Size ...........................................................................................................................10 3.2 Adaptations ............................................................................................................... 10 3.3 Diet ............................................................................................................................11 3.3.1 Types of food consumed ....................................................................................... 12 3.3.2 Seasonality of food consumed .............................................................................. 13 3.3.3 Preferred species .................................................................................................. 15 3.3.4 Amount of food ..................................................................................................... 18 3.3.5 Re-sprouting species ............................................................................................ 21 3.3.6 Distance to forage ................................................................................................. 23 3.3.7 Winter food caches ............................................................................................... 23 3.3.8 Reingestion and excrement .................................................................................. 25 4.0 Life History .................................................................................................................... 27 4.1 Colonies / Family Units .............................................................................................. 29 4.1.1 Colony composition .............................................................................................. 29 4.1.2 Colony size ........................................................................................................... 31 4.1.3 Colony density ...................................................................................................... 33 4.1.4 Colony longevity ................................................................................................... 35 4.2 Reproduction and productivity ................................................................................... 36 4.2.1 Beaver longevity ................................................................................................... 36 4.2.2 Breeding age ........................................................................................................ 36 4.2.3 Litter size .............................................................................................................. 37 4.2.4 Density dependence and impacts of harvest ......................................................... 39 4.2.5 Timing of breeding, parturition, and emergence .................................................... 40 King County Science and Technical Support Section ii April 2020 Beaver Life History and Ecology Best Science Review 4.3 Dispersal ................................................................................................................... 40 4.3.1 Challenges with learning about beaver dispersal .................................................. 41 4.3.2 Age at dispersal from the natal colony .................................................................. 42 4.3.3 Timing of dispersal ................................................................................................ 43 4.3.4 Direction of dispersal ............................................................................................ 45 4.3.5 Dispersal distance ................................................................................................ 45 4.4 Home Range and Territory ........................................................................................ 47 4.4.1 Scent mounds ....................................................................................................... 47 4.4.2 Agonistic behavior ................................................................................................ 52 4.5 Illness and Death ....................................................................................................... 53 4.5.1 Diseases and parasites ......................................................................................... 53 4.5.2 Predation .............................................................................................................. 56 4.5.3 Other causes of mortality ...................................................................................... 57 4.5.4 Mortality rates ....................................................................................................... 59 5.0 Engineering ................................................................................................................... 61 5.1 Tree cutting for food and construction material .......................................................... 61 5.1.1 Tree size preferences ........................................................................................... 61 5.1.2 Distances traversed for trees ................................................................................ 62 5.1.3 Size-distance relationship ..................................................................................... 65 5.1.4 Raft construction ................................................................................................... 66 5.1.5 Tree waste ............................................................................................................ 66 5.1.6 Beavers as farmers ............................................................................................... 67 5.2 Beaver ponds ............................................................................................................ 68 5.3 Dams .........................................................................................................................69 5.3.1 Dam site selection ................................................................................................ 70 5.3.2 Dam building and repair ........................................................................................ 72 5.3.3 Dam size ............................................................................................................... 75 5.3.4 Multiple dams per colony ...................................................................................... 76 5.4 Lodges ......................................................................................................................78 5.4.1 Island lodges ........................................................................................................ 78 5.4.2 Bank lodges .......................................................................................................... 82 5.5 Canals .......................................................................................................................84 5.5.1 Canal engineering ................................................................................................. 87 King County Science and Technical Support Section iii April 2020 Beaver Life History and Ecology Best Science Review 5.5.2 Extreme examples of ingenuity ............................................................................