This is really interesting! And the study had passed me by - thanks Fishnut!
I scihubbed the paper - seems like solid work on a first read-through. They are really talking about two things:
1) Are conservation planners paying attention to sex-specific distributions? This is assessed through a literature review, focussed on North American landbirds.
2) What implications might this have for conservation? This is assessed through a case study, the Golden-winged Warbler.
The winter distributions of migratory species are generally very poorly known, as is winter ecology in general. There is a lack of data (very few birdwatchers in tropical regions) and a lack of research (very few universities in tropical regions), so even just mapping out where a species occurs can be difficult, especially as they have stopped singing. Females are even more inconspicuous and so are more likely to get missed by surveys that aren't designed to pick them up.
In terms of sex-specific distributions, there are often ecological differences between males and females that can manifest at various scales. For example, Chaffinches split up into sex-specific flocks during winter (hence the scientific name
Fringilla coelebs - the bachelor finch), though they typically use the same kinds of habitats. In Blue Tits, the decision to migrate or not can depend on climate and food availability, but females (and young birds) are more likely to migrate than males.
In general in Passeriformes (your typical songbirds, like warblers and thrushes and sparrows) the males tend to be a bit bigger, and a bit more aggressive. In migratory species, males also tend to arrive earlier in spring in order to scrap over territories, so they also have higher food requirements during late winter to fuel a faster migration. The consequence of this can be that males will outcompete females and occupy higher-quality habitat, which is what is seen in the Golden-winged Warbler. However, according to the article, this has led some authors to argue that male-dominated habitats should be prioritised as they are of higher quality.
It would be interesting to compare these results with other groups of birds. There are quite a lot of species which aren't sexually dimorphic, so you wouldn't necessarily expect this pattern to arise. On the other hands, in a lot of wader species the females are larger and have longer beaks, which means they can access more food than males.
tom p wrote: Wed Nov 20, 2019 1:13 pm
That's just ridiculous.
If memory serves, in many species (apart from those that pair up for life), isn't it the females we would most need to protect, since a male can fertilise many females in a season, but each female can usually only be fertilised once a season?
In which case, were there to be a bias for conservation, it should be in the other direction.
Female birds tend to be fertilised once per egg, so up to perhaps a dozen times per season, but pedantry aside yes - a female-biased sex ratio in most cases would be better for productivity than a male bias. The article points out, however, that in species of conservation concern male-biased sex ratios are more common.
BTW, even in species that pair for life, they (a) are normally cheating bastards at a genetic level, and (b) will readily re-pair if their mate cops it or moves on or whatever. They don't just pine to death when there's shagging to be done.
dyqik wrote: Wed Nov 20, 2019 2:18 pm
I can form a quick guess at how such a bias starts or is maintained, even with the best intentions.
Male birds are usually much more recognizable than female ones, with lots of female birds being LBBs, while the males are distinctive. A fair number of identification guides only prominently show the males as well (e.g.
Audubon guide) Although looking at Wikipedia, which has male and female images prominent, the golden wing warblers aren't as disparate in appearance as many species (c.f. male and female northern cardinals, for example)
That may well lead to sites where females overwinter not being identified as readily, and so not attracting attention, both for conservation and description.
Dimorphism is part of it; however, the article points out that sex-specific distributions are better documented in more dimorphic species, and that there are probably also research biases at play in terms of what questions are asked. By looking just for 'individuals of species X' without specifically considering where
females of that species might be, researchers appear to be systematically under-documenting female distributions and thus leaving them out of conservation planning.
Woodchopper wrote: Thu Nov 21, 2019 12:09 pm
I was also wondering about this:
”Among the small songbird species that have been studied, the general rule seems to be that females occupy lower elevation, shrubbier, drier sites," says lead author Ruth Bennett. "Mid-elevation and high-elevation sites that are more humid and have better quality forest are occupied by males."
The forest inhabited by the male birds might have higher status among politicians and activists who call for conservation sites (and the people who donate to them).
“Save the rainforest!” is an easier sell than “Save the arid scrubland!”.
Equally, it's easier to convince politicians in developing countries to declare some high-elevation cloud forest as a reserve - remote, inaccessible sites that would be difficult to farm and have no commercially-valuable timber - than to implement (and crucially
enforce) management changes in a working agricultural landscape. Even in rich areas like Europe that
piss spend millions a year on "agri-environment schemes" have farmland birds declining at a faster rate than any other group.
Grumble wrote: Thu Nov 21, 2019 7:55 pm
It wouldn’t have occurred to me, not being any kind of ornithologist, that males and females of the same species wouldn’t live in the same habitats.
During the breeding season they generally do, for obvious reasons - though if one sex isn't so involved in tending the nest/chicks they may range more widely out of suitable breeding habitat. Parental care is hugely variable in birds, even within species.
