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Fear of car­ni­vores good for ecosys­tem health: a rac­coon study

pub­lished 27 Feb­ru­ary 2016 | mod­i­fied 27 Feb­ru­ary 2016

Raccoon in treeAn exper­i­ment involv­ing rac­coons and speak­ers emit­ting the sound of bark­ing dogs on tracts of beaches on British Columbia’s Gulf Islands shows that the fear of large car­ni­vores has a pos­i­tive impact on ecosys­tem health. The study led by Uni­ver­sity of Vic­to­ria PhD stu­dent Justin Suraci with sup­port of the Rain­coast Con­ser­va­tion Foun­da­tion is pub­lished on 23 Feb­ru­ary in Nature Com­mu­ni­ca­tions.

Rac­coons on the British Columbia’s Gulf Islands are dev­as­tat­ing pop­u­la­tions of crabs and fish in the inter­tidal zone, and nest­ing song­birds on land. Suraci and co-​researchers Liana Zanette (West­ern Uni­ver­sity) and Larry Dill (Simon Fraser Uni­ver­sity) sus­pected this was due to rac­coons hav­ing lit­tle to fear, because the for­merly noc­tur­nal rac­coon pop­u­la­tions now for­age unabashedly day and night in the inter­tidal zones.

What hap­pens when island rac­coons live free of preda­tors? A lot. And it’s not good.
Rac­coons are cocker-​spaniel-​sized crea­tures native to the Amer­i­cas. Nor­mally, rac­coons are meso­preda­tors — ani­mals in the mid­dle of the food chain — part of an eco­log­i­cal niche they share with other medium-​sized omni­vores, such as skunks, bad­gers, and foxes. But on some of British Columbia’s Gulf Islands, rac­coon pop­u­la­tions have no nat­ural preda­tors and no fear of becom­ing another animal’s lunch. Fol­low ecol­o­gists Mike Clinchy and Justin Suraci in the field as they study the effects of rac­coons for­ag­ing in the inter­tidal zone, barely watch­ing for dan­ger as they rip apart count­less crabs and other prey species

(Source: Hakai Mag­a­zine Vimeo channel)

To inves­ti­gate whether fear of dogs — a top (or apex) preda­tor since the elim­i­na­tion of wolves, bears and cougars from the Islands almost a cen­tury ago — could affect rac­coon for­ag­ing behav­iours along the shore­line, they played threat­en­ing dog sounds from speak­ers along exten­sive tracts of shore­line for one month.

Raccoon study fear of dogbarkFear of large car­ni­vores caused a trophic cas­cade. Dia­gram illus­trat­ing how broad­cast­ing play­backs of large car­ni­vore vocal­iza­tions affected mul­ti­ple lower trophic lev­els. Green and red arrows rep­re­sent pos­i­tive and neg­a­tive effects, respec­tively, on for­ag­ing, abun­dance or sur­vival. Solid arrows con­nect preda­tor and prey; dashed arrows con­nect species affected, but not directly eaten, by another.
Suraci, J. P. et al. Fear of large car­ni­vores causes a trophic cas­cade. Nat. Com­mun. 7:10698 doi: 10.1038/ncomms10698 (2016). Licensed under a Cre­ative Com­mons Attri­bu­tion 4.0 Inter­na­tional License.

See how the rac­coons flee from the recorded barks:

(Source: New Sci­en­tists YouTube channel)

They found that rac­coons reduced their for­ag­ing time by 66 per cent. In that period, researchers recorded a 61 per­cent increase in the abun­dance of red rock crab and an 81 per cent increase in inter­tidal fish — a prime tar­get of raccoons.

Humans have done an excel­lent job of wip­ing out large car­ni­vores across the globe and we’re only start­ing to under­stand what the eco­log­i­cal con­se­quences of that are,” says Suraci. “One of the major con­se­quences is that when you take away the large car­ni­vores, you get out­breaks of the species that they eat — her­bi­vores like deer and smaller preda­tors like rac­coons. So, under­stand­ing the ways in which these large car­ni­vores his­tor­i­cally kept their prey in check was very impor­tant to restor­ing these ecosystems.”

Justin Suraci, lead author, Depart­ment of Biol­ogy, Uni­ver­sity of Vic­to­ria, British Colum­bia, Canada:

What we’ve shown is that we have to con­sider the behav­ioural inter­ac­tions top preda­tors have with their prey and not just the actual pre­da­tion — the killing and con­sump­tion — when we’re think­ing about how to restore ecosys­tems from which large car­ni­vores have been lost.

(Source: Uni­ver­sity of Vic­to­ria media release, 23.02.2016)

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