Spring asynchrony in migratory birds

15 05 2017

Brent geese flock in the Limfjorden (Denmark)courtesy of Kevin Clausen. The Brent goose (Branta bernicla) is a migratory goose that breeds in Arctic coasts, as well as in northern Eurasia and the Americas, starting from late May to early June. Adults are about 0.5 m long, weigh some 2 kg and live up to 30 years. Their nests are placed in the ground, where reproductive pairs incubate a single clutch (≤ 5 eggs) for a couple of months. They are herbivores, feeding on algae (mainly Zostera marina in Limfjord) and seagrass in estuaries, fjords, intertidal areas and rocky beaches during fall and winter. During summer they feed on tundra herbs, moss, lichens, as well as aquatic plants in rivers and lakes. The species is ‘Least Concern’ for the IUCN, with a global population at some 600,000 individuals.

Migratory birds synchronise their travel from non-breeding to breeding quarters with the seasonal conditions optimal for reproduction. Above all, they decide when to migrate on the basis of the climate of their wintering areas while they are there. As climate change involves earlier springs in the Arctic but not in the wintering areas, there is a lack of synchronisation that leads to a demographic decline of these birds in the polar regions where they breed.

When I think about how species respond to climate change, the song from the ClashShould I stay or should I go” comes to mind. As climate changes, species eventually have to face an ultimate choice: (i) stay and adapt to novel conditions or become locally extinct if adaptation fails, (ii) or move to other regions where climatic conditions should be more suitable. Migratory species have to face this decision every time they have to move back and forth from non-breeding to breeding grounds.

Migration is a behavioural strategy shared by different animal groups like sea turtles, mammals, amphibians, insects or birds. Species move from one area to another usually to feed and reproduce in the best climatic conditions possible. For birds, migration is a common phenomenon that typically entails large movements between breeding and wintering grounds. These vertebrates boast some of the longest migratory distances known in the animal kingdom, particularly seabirds like Artic terns, which can complete up to a round-world trip in a single migratory event between the UK and the Antarctic (1). There are several theories about the mechanisms triggering bird migration, including improving body condition and fitness through unexploited resources (2), reducing parasite load (3), minimizing predation risk (4), maximizing day-light (5), or reducing competition (6, 7). Whatever the cause, birds have to decide when the best moment to migrate is, counting only with the (usually climatic) clues they have at the departure site. Read the rest of this entry »

What immigration means for Australia’s climate-change policies

12 06 2016

After dipping my foot into the murky waters of human population demography a few years ago, I’m a little surprised that I find myself here again. But this time I’m not examining what the future of the global human population might be and what it could mean for our environment; instead, I’m focussing on Australia’s population future and its implications for our greenhouse-gas emissions trajectories.

Just published in Asia and the Pacific Policy Forum1, my paper with long-time co-author Barry Brook is entitled Implications of Australia’s population policy for future greenhouse gas emissions targets. It deals with the sticky question of just how many people Australia can ‘afford’ to house. By ‘afford’ I mean several things, but most specifically in the context of this paper is by how much we need to reduce our per capita emissions to achieve future reduction targets under various immigration-rate scenarios.

In many ways Australia’s population is typical of other developed nations in that its intrinsic fertility (1.78 children/woman) is below replacement (which is itself ~ 2.1 children/female). Yet Australia’s population grew nearly twice (1.88×) as large from 1971 to 2014. It doesn’t take a genius to figure out that most of our population growth is due to net immigration.

In fact, between 2006 and 2014, Australia welcomed a net of 215,000 new people per year (this means that of all the permanent immigrants and emigrants, a ‘net’ of approximately 215,000 stayed each year), which represents about 1% of our total population size (that latter most likely just ticked over 24 million). Read the rest of this entry »

Whither goest the biggest fish?

7 02 2013
© W Osborn (AIMS)

© W Osborn (AIMS)

Well, since my own institute beat me to the punch on announcing our latest whale shark paper (really, far too keen, ladies & gents), I thought I’d better follow up with a post of my own.

We’ve mentioned our previous whale shark research before (see here and here for previous posts, and see the end of this post for a full list of our whale shark publications), but this is a lovely extension of that work by my recently completed PhD student, Ana Sequeira.

Her latest contribution, Inferred global connectivity of whale shark Rhincodon typus populations just published online in Journal of Fish Biology, describes what a lot of whale shark punters & researchers alike have suspected for a long time – global connectivity of all the oceans’ whale shark populations. The problem hasn’t been a lack of ‘evidence’ for this per se; there is now sufficient evidence from genetic studies that at least on the generational scale (a single generation could be up to 37 years long), populations among the major ocean basins are connected via migration (Castro et al. 2007Schmidt et al. 2009). The problem instead is that no one has ever observed a shark voyage between ocean basins, nor has anyone really suggested how and over what time scales this (must) happen.

Until now, that is. Read the rest of this entry »