next message in archive
no next message in thread
previous message in archive
previous message in thread
Index of Subjects
Index of Subjects --20cf307d04a04574c404c95c93fc Content-Type: text/plain; charset=ISO-8859-1 Hi folks, Some additional thoughts, from another non-expert, on a neat topic... I'd add that if zugunruhe (loosely, impulse to migrate) and migration behaviour are not entirely genetically controlled (which seems to be the case) males and females should be expected to experience different selective pressures in terms of timing of migration from breeding grounds to wintering grounds related to differences in costs and benefits to males and females of leaving vs. staying. This might differ based on things such as the distance between breeding and wintering grounds, seasonality of risk (food availability, climate/weather patterns, predator abundance/distribution etc), mating system (as Chris and Rick allude to) physiological and/or genetic constraints and environmental/social conditions experienced on wintering grounds. I would guess, that these factors should also lead to differences in the relative timing between males and females among species but also among m/f of the same species in different geographic locations (i.e., no population-level selection; but perhaps depends on definition of 'population'). Since ruby-throats are polygamous, and males are reported as not providing parental care, there could be significant fitness benefit to males of sticking around so they could achieve additional fertilizations with late-breeding or re-nesting females (not sure if there is any evidence of this for hummingbirds?). But perhaps the potential benefit of this is outweighed by other factors such as resource availability during migration, securing a good wintering territory, or physiological constraints. cheers, James. On Mon, Sep 10, 2012 at 1:09 PM, Rick Whitman < dendroica.caerulescens@gmail.com> wrote: > Natural selection will select for early male departure on both an > individual (survival) basis and on a population-wide basis. The males > contribute nothing to nestling survival. They may as well get going > early while things are great all along the route south. This also > frees up food resources for the later females & juveniles. The > juveniles no doubt need to mature & build up maximum fat reserves > before they undertake their first migration, for which they have no > experience, aside from instinct, and on which they may make some > errors. > > There are analogies in the way in which most shorebird species depart > from the North. In many cases the adults leave first & in some species > (aside from phalaropes) I believe the females leave before the males. > They are burned out & need to start south for the richer staging areas > like James Bay & Bay of Fundy. The males go next & juveniles last. The > juveniles that don't have the skills to feed themselves & bulk up > before leaving may not complete their first migration. So be it. > > Whatever works on a population-wide AND individual basis will be > selected, over time. > > Top of the head comments; I don't teach this stuff, etc. > > Rick W. > > On Mon, Sep 10, 2012 at 11:41 AM, Christopher Majka > <c.majka@ns.sympatico.ca> wrote: > > Hi Andy, > > > > As I understand it, at least in terms of spring migration, the thought is > > that males of some species (including Ruby-throated, Rufous, Allens, and > > Calliope hummingbirds) migrate first to stake out territories. Females > > follow some 2-3 weeks later to be able to take advantage of a > nutritionally > > richer supply of flowers along the migration route. On the southward > > migration, juveniles tend to follow females. > > > > I know there has been a lot of investigation on survivorship of > hummingbirds > > related to the timing of migration, what plants are in bloom over what > > portion of the migration route, and the ability to stake out territories > in > > optimal/suboptimal habitat. The situation with respect to hummingbirds is > > also somewhat different from many other birds since male hummingbirds are > > polygamous and because of the nutritional requirements and physiology of > > hummingbirds. > > > > I don't have the time to investigate further but perhaps someone on the > list > > will know more. > > > > Cheers! > > > > Chris > > > > On 10-Sep-12, at 10:12 AM, andy dean wrote: > > > >> Our son-in-law is a budding birder and asked us an interesting question > >> which we couldn't answer. > >> Why do male hummingbirds migrate ahead of the females? Anybody know the > >> answer? > >> > >> Andy and Lelia Dean > >> 86 Baden Powell Drive > >> Kentville, N.S. > >> (902) 678-6243 > >> > >> > -- James Churchill Kentville, Nova Scotia Email: jameslchurchill@gmail.com Phone (h): (902) 681-2374 Skype: jameslchurchill --20cf307d04a04574c404c95c93fc Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Hi folks, <br>Some additional thoughts, from another non-expert, on a neat = topic...<br><br>I'd add that if zugunruhe (loosely, impulse to migrate)= and migration behaviour are not entirely genetically controlled (which see= ms to be the case) males and females should be expected to experience diffe= rent selective pressures in terms of timing of migration from breeding grou= nds to wintering grounds related to differences in costs and benefits to ma= les and females of leaving vs. staying. <br> <br>This might differ based on things such as the distance between breeding= and wintering grounds, seasonality of risk (food availability, climate/wea= ther patterns, predator abundance/distribution etc), mating system (as Chri= s and Rick allude to) physiological and/or genetic constraints and environm= ental/social conditions experienced on wintering grounds. I would guess, th= at these factors should also lead to differences in the relative timing bet= ween males and females among species but also among m/f of the same species= in different geographic locations (i.e., no population-level selection; bu= t perhaps depends on definition of 'population').<br> <br>Since ruby-throats are polygamous, and males are reported as not provid= ing parental care, there could be significant fitness benefit to males of s= ticking around so they could achieve additional fertilizations with late-br= eeding or re-nesting females (not sure if there is any evidence of this for= hummingbirds?). But perhaps the potential benefit of this is outweighed by= other factors such as resource availability during migration, securing a g= ood wintering territory, or physiological constraints.<br> <br>cheers, <br>James. <br><br><br><br><div class=3D"gmail_quote">On Mon, S= ep 10, 2012 at 1:09 PM, Rick Whitman <span dir=3D"ltr"><<a href=3D"mailt= o:dendroica.caerulescens@gmail.com" target=3D"_blank">dendroica.caerulescen= s@gmail.com</a>></span> wrote:<br> <blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1p= x #ccc solid;padding-left:1ex">Natural selection will select for early male= departure on both an<br> individual (survival) basis and on a population-wide basis. The males<br> contribute nothing to nestling survival. They may as well get going<br> early while things are great all along the route south. This also<br> frees up food resources for the later females & juveniles. The<br> juveniles no doubt need to mature & build up maximum fat reserves<br> before they undertake their first migration, for which they have no<br> experience, aside from instinct, and on which they may make some<br> errors.<br> <br> There are analogies in the way in which most shorebird species depart<br> from the North. In many cases the adults leave first & in some species<= br> (aside from phalaropes) I believe the females leave before the males.<br> They are burned out & need to start south for the richer staging areas<= br> like James Bay & Bay of Fundy. The males go next & juveniles last. = The<br> juveniles that don't have the skills to feed themselves & bulk up<b= r> before leaving may not complete their first migration. So be it.<br> <br> Whatever works on a population-wide AND individual basis will be<br> selected, over time.<br> <br> Top of the head comments; I don't teach this stuff, etc.<br> <br> Rick W.<br> <div><div><br> On Mon, Sep 10, 2012 at 11:41 AM, Christopher Majka<br> <<a href=3D"mailto:c.majka@ns.sympatico.ca" target=3D"_blank">c.majka@ns= .sympatico.ca</a>> wrote:<br> > Hi Andy,<br> ><br> > As I understand it, at least in terms of spring migration, the thought= is<br> > that males of some species (including Ruby-throated, Rufous, Allens, a= nd<br> > Calliope hummingbirds) migrate first to stake out territories. Females= <br> > follow some 2-3 weeks later to be able to take advantage of a nutritio= nally<br> > richer supply of flowers along the migration route. On the southward<b= r> > migration, juveniles tend to follow females.<br> ><br> > I know there has been a lot of investigation on survivorship of hummin= gbirds<br> > related to the timing of migration, what plants are in bloom over what= <br> > portion of the migration route, and the ability to stake out territori= es in<br> > optimal/suboptimal habitat. The situation with respect to hummingbirds= is<br> > also somewhat different from many other birds since male hummingbirds = are<br> > polygamous and because of the nutritional requirements and physiology = of<br> > hummingbirds.<br> ><br> > I don't have the time to investigate further but perhaps someone o= n the list<br> > will know more.<br> ><br> > Cheers!<br> ><br> > Chris<br> ><br> > On 10-Sep-12, at 10:12 AM, andy dean wrote:<br> ><br> >> Our son-in-law is a budding birder and asked us an interesting que= stion<br> >> which we couldn't answer.<br> >> Why do male hummingbirds migrate ahead of the females? =A0Anybody = know the<br> >> answer?<br> >><br> >> Andy and Lelia Dean<br> >> 86 Baden Powell Drive<br> >> Kentville, N.S.<br> >> <a href=3D"tel:%28902%29%20678-6243" value=3D"+19026786243" target= =3D"_blank">(902) 678-6243</a><br> >><br> >><br> </div></div></blockquote></div><br><br clear=3D"all"><br>-- <br>James Churc= hill<br>Kentville, Nova Scotia<br>Email: <a href=3D"mailto:jameslchurchill@= gmail.com" target=3D"_blank">jameslchurchill@gmail.com</a><br>Phone (h): <a= href=3D"tel:%28902%29%20681-2374" value=3D"+19026812374" target=3D"_blank"= >(902) 681-2374</a><br> Skype: jameslchurchill<br><br><br><br> --20cf307d04a04574c404c95c93fc--
next message in archive
no next message in thread
previous message in archive
previous message in thread
Index of Subjects