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--Apple-Mail-7-646997005 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed Lance and all, THANKS for this thread and especially Lance's notes, because I have been wondering since I arrived here in the 1970s how the double-crested cormorants do so well along the Fundy and especially Minas Basin coasts with our very turbid water? whereas coastal ospreys are very rarely seen here and, in the Minas Basin, we don't see many diving ducks and the loons are mainly transients. Perhaps Lance has answered my question to a large extent. Perhaps also the cormorants do much of their foraging during the mythical periods of "slack tide" when some of the suspended material drops downward and the water "clears" quite a bit for a short period of time, until the tidal water starts moving again and then looking like liquid soil. Cheers from Jim in Wolfville. Begin forwarded message: > From: "Laviolette, Lance (EXP)" <lance.laviolette@lmco.com> > Date: February 18, 2013 12:07:03 PM AST > To: "naturens@chebucto.ns.ca" <naturens@chebucto.ns.ca> > Subject: RE: [NatureNS] "Scoping" waterfowl footnote > Reply-To: naturens@chebucto.ns.ca > > Hi Everyone, > > Ian McLaren wrote: > "So the question remains, why don't cormorants scope? They can set > the dive reflex readily enough, as Nancy indicates. Am I missing > something?" > > I originally thought the answer to this question might be as simple > as cormorants see underwater much better than other birds so don't > need to scope from above the waterline. I'd read somewhere that > their green eye colour allowed them to see better in low light > conditions. However, I came across the following 2007 paper by > Craig R. White, Norman Day, Patrick J. Butler, Graham R. Martin > titled "Vision and Foraging in Cormorants: More like Herons than > Hawks?" In the paper they describe how they measured the vision of > Great Cormorants and found it unexpectedly poor, about the > equivalent of human vision underwater, and inferior to avian aerial > predators. Their conclusion however may hold, at least in part, the > answer to the above question: > > "Their efficient hunting involves the use of specialised foraging > techniques which employ brief short-distance pursuit and/or rapid > neck extension to capture prey that is visually detected or flushed > only at short range." > > The authors also note that cormorants show "... the highest known > foraging yield for a marine predator...". > > In the Birds of North America account, Jeremy J. Hatch and D. V. > Weseloh note that there are a number of special adaptations of the > eye of the cormorant which suggest that they have effective > underwater vision but the authors conclude that: > > "Double-crested Cormorants commonly catch bottom-dwelling fish in > turbid water where visibility is very low, so tactile sensitivity > may be important for both locating and capturing prey" > > The simple answer appears to be that cormorants don't need to scope > having evolved a hunting technique without its use which is > extremely effective. > > All the best, > > Lance > > Lance Laviolette > Glen Robertson, Ontario > > --Apple-Mail-7-646997005 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=US-ASCII <html><body style=3D"word-wrap: break-word; -webkit-nbsp-mode: space; = -webkit-line-break: after-white-space; "> Lance and all, THANKS for this thread and especially Lance's notes, = because I have been wondering since I arrived here in the 1970s how the = double-crested cormorants do so well along the Fundy and especially = Minas Basin coasts with our very turbid water? whereas coastal ospreys = are very rarely seen here and, in the Minas Basin, we don't see many = diving ducks and the loons are mainly transients. Perhaps Lance = has answered my question to a large extent. Perhaps also the = cormorants do much of their foraging during the mythical periods of = "slack tide" when some of the suspended material drops downward and the = water "clears" quite a bit for a short period of time, until the tidal = water starts moving again and then looking like liquid soil. = <div><br></div><div>Cheers from Jim in = Wolfville.<br><div><br><div>Begin forwarded message:</div><br = class=3D"Apple-interchange-newline"><blockquote type=3D"cite"><div = style=3D"margin-top: 0px; margin-right: 0px; margin-bottom: 0px; = margin-left: 0px; "><font face=3D"Helvetica" size=3D"3" color=3D"#000000" = style=3D"font: 12.0px Helvetica; color: #000000"><b>From: = </b></font><font face=3D"Helvetica" size=3D"3" style=3D"font: 12.0px = Helvetica">"Laviolette, Lance (EXP)" <<a = href=3D"mailto:lance.laviolette@lmco.com">lance.laviolette@lmco.com</a>>= ;</font></div><div style=3D"margin-top: 0px; margin-right: 0px; = margin-bottom: 0px; margin-left: 0px; "><font face=3D"Helvetica" = size=3D"3" color=3D"#000000" style=3D"font: 12.0px Helvetica; color: = #000000"><b>Date: </b></font><font face=3D"Helvetica" size=3D"3" = style=3D"font: 12.0px Helvetica">February 18, 2013 12:07:03 PM = AST</font></div><div style=3D"margin-top: 0px; margin-right: 0px; = margin-bottom: 0px; margin-left: 0px; "><font face=3D"Helvetica" = size=3D"3" color=3D"#000000" style=3D"font: 12.0px Helvetica; color: = #000000"><b>To: </b></font><font face=3D"Helvetica" size=3D"3" = style=3D"font: 12.0px Helvetica">"<a = href=3D"mailto:naturens@chebucto.ns.ca">naturens@chebucto.ns.ca</a>" = <<a = href=3D"mailto:naturens@chebucto.ns.ca">naturens@chebucto.ns.ca</a>></f= ont></div><div style=3D"margin-top: 0px; margin-right: 0px; = margin-bottom: 0px; margin-left: 0px; "><font face=3D"Helvetica" = size=3D"3" color=3D"#000000" style=3D"font: 12.0px Helvetica; color: = #000000"><b>Subject: </b></font><font face=3D"Helvetica" size=3D"3" = style=3D"font: 12.0px Helvetica"><b>RE:<span = class=3D"Apple-converted-space"> </span>[NatureNS]<span = class=3D"Apple-converted-space"> </span>"Scoping" waterfowl = footnote</b></font></div><div style=3D"margin-top: 0px; margin-right: = 0px; margin-bottom: 0px; margin-left: 0px; "><font face=3D"Helvetica" = size=3D"3" color=3D"#000000" style=3D"font: 12.0px Helvetica; color: = #000000"><b>Reply-To: </b></font><font face=3D"Helvetica" size=3D"3" = style=3D"font: 12.0px Helvetica"><a = href=3D"mailto:naturens@chebucto.ns.ca">naturens@chebucto.ns.ca</a></font>= </div><div style=3D"margin-top: 0px; margin-right: 0px; margin-bottom: = 0px; margin-left: 0px; min-height: 14px; "><br></div> <div = style=3D"margin-top: 0px; margin-right: 0px; margin-bottom: 0px; = margin-left: 0px; ">Hi Everyone,</div><div style=3D"margin-top: 0px; = margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: = 14px; "><br></div><div style=3D"margin-top: 0px; margin-right: 0px; = margin-bottom: 0px; margin-left: 0px; ">Ian McLaren wrote:</div><div = style=3D"margin-top: 0px; margin-right: 0px; margin-bottom: 0px; = margin-left: 0px; ">"So the question remains, why don't cormorants = scope? They can set the dive reflex readily enough, as Nancy indicates. = Am I missing something?"</div><div style=3D"margin-top: 0px; = margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: = 14px; "><br></div><div style=3D"margin-top: 0px; margin-right: 0px; = margin-bottom: 0px; margin-left: 0px; ">I originally thought the answer = to this question might be as simple as cormorants see underwater much = better than other birds so don't need to scope from above the waterline. = I'd read somewhere that their green eye colour allowed them to see = better in low light conditions. However, I came across the following = 2007 paper by Craig R. White, Norman Day, Patrick J. Butler, Graham R. = Martin titled "Vision and Foraging in Cormorants: More like Herons than = Hawks?" In the paper they describe how they measured the vision of Great = Cormorants and found it unexpectedly poor, about the equivalent of human = vision underwater, and inferior to avian aerial predators. Their = conclusion however may hold, at least in part, the answer to the above = question:</div><div style=3D"margin-top: 0px; margin-right: 0px; = margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><br></div><div = style=3D"margin-top: 0px; margin-right: 0px; margin-bottom: 0px; = margin-left: 0px; ">"Their efficient hunting involves the use of = specialised foraging techniques which employ brief short-distance = pursuit and/or rapid neck extension to capture prey that is visually = detected or flushed only at short range."</div><div style=3D"margin-top: = 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; = min-height: 14px; "><br></div><div style=3D"margin-top: 0px; = margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">The authors = also note that cormorants show "... the highest known foraging yield for = a marine predator...".</div><div style=3D"margin-top: 0px; margin-right: = 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; = "><br></div><div style=3D"margin-top: 0px; margin-right: 0px; = margin-bottom: 0px; margin-left: 0px; ">In the Birds of North America = account, Jeremy J. Hatch and D. V. Weseloh note that there are a number = of special adaptations of the eye of the cormorant which suggest that = they have effective underwater vision but the authors conclude = that:</div><div style=3D"margin-top: 0px; margin-right: 0px; = margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><br></div><div = style=3D"margin-top: 0px; margin-right: 0px; margin-bottom: 0px; = margin-left: 0px; ">"Double-crested Cormorants commonly catch = bottom-dwelling fish in turbid water where visibility is very low, so = tactile sensitivity may be important for both locating and capturing = prey"</div><div style=3D"margin-top: 0px; margin-right: 0px; = margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><br></div><div = style=3D"margin-top: 0px; margin-right: 0px; margin-bottom: 0px; = margin-left: 0px; ">The simple answer appears to be that cormorants = don't need to scope having evolved a hunting technique without its use = which is extremely effective.</div><div style=3D"margin-top: 0px; = margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: = 14px; "><br></div><div style=3D"margin-top: 0px; margin-right: 0px; = margin-bottom: 0px; margin-left: 0px; ">All the best,</div><div = style=3D"margin-top: 0px; margin-right: 0px; margin-bottom: 0px; = margin-left: 0px; min-height: 14px; "><br></div><div style=3D"margin-top: = 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; = ">Lance</div><div style=3D"margin-top: 0px; margin-right: 0px; = margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><br></div><div = style=3D"margin-top: 0px; margin-right: 0px; margin-bottom: 0px; = margin-left: 0px; ">Lance Laviolette</div><div style=3D"margin-top: 0px; = margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Glen = Robertson, Ontario</div><div style=3D"margin-top: 0px; margin-right: = 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; = "><br></div><div style=3D"margin-top: 0px; margin-right: 0px; = margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><br></div> = </blockquote></div><br></div></body></html>= --Apple-Mail-7-646997005--
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