January 25, 2016
G and I took the day off today, so no fun excursions or scans to report on. So, I thought today would be a good day to explain why I’m so interested in finding those green flagged birds from my breeding population.
I mentioned in an earlier post that it’s very, very rare for a breeding population study to ‘know’ where individuals are for the rest of the year. There’s only a handful of migratory species where that’s known, though technologies like geolocators are making that possible for more and more species.
Nathan, the previous grad student who started the godwit project, used geolocators to track individuals throughout the year and discovered not only their migration pathways, but also that the Alaska breeding population over-winters on Chiloé while the Eastern Canadian population over-winters in Southern Argentina. There was 'high connectivity’ between the breeding site and a particular non-breeding site meaning most individuals from a breeding site winter together.
Now that we know where individuals are the seven months of the year that they aren’t in Alaska (or flying back and forth) there are some interesting questions we can ask. There’s a huge body of theory hypothesizing that the conditions an individual faces during the non-breeding season can actually affect fitness (a measure of reproductive success) at a later date. The key there is that you may have to understand something about what happened in the year prior to a breeding season to understand why an individual may have higher or lower nesting success and not just what we see on the breeding grounds. It’s the transition to a later date affecting reproduction that’s critical. It’s called 'seasonal carry-over effects’ because they carry-over from one season to a later one.
A lot of work has been done on this idea, that was pioneered by the American Redstart project G and I worked on in Jamaica, most of which uses technology or innovative ways to test this rather than tracking individuals - mostly because that has been impossible up until these technological advances that let us put geolocators and satellite transmitters on smaller and smaller birds.
For instance, the Redstart project has shown that individuals that winter in the high quality mangrove habitat (mostly older dominant males) have higher reproductive success than individuals that spent the winter in the lower quality scrub habitat. They did this not by following the same individuals but using isotope signatures of nesting birds to determine which habitat they spent the winter in - neat huh?
A few studies have begun to track individuals now too - including Nathan. He used the data from the geolocators to test another idea from the redstart project - that the greatest effect may not be habitat quality but timing of annual cycle events. He looked to see if a bird was delayed in leaving Chile or took longer on migration north if they had fewer young. Or if they arrived to Chiloé late if they had fewer young. Nathan found no effect and hypothesized that the habitat quality on Chiloé was so good that an individual can recover from a late southbound migration with no effect or store up energy to compensate for any event post Chiloé.
I want to follow up on that idea and test if the habitat an individual uses on Chiloé affects their reproductive success in future years. I’m specifically targeting green flagged birds because they’re my breeding population - I can get data on their reproductive success this summer in Alaska - and I won’t know anything about the breeding success of the thousands of other godwits that we see.
I’m using a three pronged axis to compare habitat quality between bays - food availability, predator risk, and human caused disturbances. I’m doing so using a number of different techniques including focal observations of individuals. I'll talk more about each one of these as the season progresses.
My idea is to take the information I have about the habitat quality and body condition of individuals in Alaska and see if there is any influence on their reproductive success.
G and I took the day off today, so no fun excursions or scans to report on. So, I thought today would be a good day to explain why I’m so interested in finding those green flagged birds from my breeding population.
I mentioned in an earlier post that it’s very, very rare for a breeding population study to ‘know’ where individuals are for the rest of the year. There’s only a handful of migratory species where that’s known, though technologies like geolocators are making that possible for more and more species.
Nathan, the previous grad student who started the godwit project, used geolocators to track individuals throughout the year and discovered not only their migration pathways, but also that the Alaska breeding population over-winters on Chiloé while the Eastern Canadian population over-winters in Southern Argentina. There was 'high connectivity’ between the breeding site and a particular non-breeding site meaning most individuals from a breeding site winter together.
Now that we know where individuals are the seven months of the year that they aren’t in Alaska (or flying back and forth) there are some interesting questions we can ask. There’s a huge body of theory hypothesizing that the conditions an individual faces during the non-breeding season can actually affect fitness (a measure of reproductive success) at a later date. The key there is that you may have to understand something about what happened in the year prior to a breeding season to understand why an individual may have higher or lower nesting success and not just what we see on the breeding grounds. It’s the transition to a later date affecting reproduction that’s critical. It’s called 'seasonal carry-over effects’ because they carry-over from one season to a later one.
A lot of work has been done on this idea, that was pioneered by the American Redstart project G and I worked on in Jamaica, most of which uses technology or innovative ways to test this rather than tracking individuals - mostly because that has been impossible up until these technological advances that let us put geolocators and satellite transmitters on smaller and smaller birds.
For instance, the Redstart project has shown that individuals that winter in the high quality mangrove habitat (mostly older dominant males) have higher reproductive success than individuals that spent the winter in the lower quality scrub habitat. They did this not by following the same individuals but using isotope signatures of nesting birds to determine which habitat they spent the winter in - neat huh?
A few studies have begun to track individuals now too - including Nathan. He used the data from the geolocators to test another idea from the redstart project - that the greatest effect may not be habitat quality but timing of annual cycle events. He looked to see if a bird was delayed in leaving Chile or took longer on migration north if they had fewer young. Or if they arrived to Chiloé late if they had fewer young. Nathan found no effect and hypothesized that the habitat quality on Chiloé was so good that an individual can recover from a late southbound migration with no effect or store up energy to compensate for any event post Chiloé.
I want to follow up on that idea and test if the habitat an individual uses on Chiloé affects their reproductive success in future years. I’m specifically targeting green flagged birds because they’re my breeding population - I can get data on their reproductive success this summer in Alaska - and I won’t know anything about the breeding success of the thousands of other godwits that we see.
I’m using a three pronged axis to compare habitat quality between bays - food availability, predator risk, and human caused disturbances. I’m doing so using a number of different techniques including focal observations of individuals. I'll talk more about each one of these as the season progresses.
My idea is to take the information I have about the habitat quality and body condition of individuals in Alaska and see if there is any influence on their reproductive success.