Pleistocene to historic shifts in bald eagle diets on the Channel Islands, California
Bald eagles, once common in ecosystems around the Channel Islands
(CI) in California, have stopped breeding on the islands in recent decades due
to the introduction of the agricultural pesticide DDT. Although recent efforts
to restore these breeding populations on Northern CI (NCI) seem promising,
background DDT concentrations in marine ecosystems are still limiting
reproductive success. The authors set out to characterize any shifts in bald
eagles' diets (marine vs. terrestrial) that may have followed human
introduction onto the CI.
To do this, the authors study the
stable isotopes obtained from bald eagle collagen and keratin from the
Pleistocene to the mid-20th century, and compared these isotopic compositions
to those of the eagles' prey. This is done knowing (1) marine consumers have
higher 15N than terrestrial consumers, due to more trophic levels in
marine ecosystems, (2) marine consumers have higher 13C than
terrestrial consumers, due to the plant types in each realm, and (3) consumers'
isotopic compositions reflect these marine or terrestrial resources. This third
rule is especially important, given that bald eagles are generalists that will
eat almost anything available to them; the bald eagles on CI eat a variety of
fish, mammals, and other birds, and their preference depends on the
availability of each food source.
The resulting isotopic compositions
of historic and prehistoric bald eagles from the NCI indicate a shift from
marine to terrestrial prey in the diets, lining up nicely with Spanish
colonization and later introduction of ranching in the area. Isotopic
compositions taken regionally (i.e., the rest of the CI and adjacent mainland)
indicate a mixture of marine and terrestrial prey in bald eagle diets,
consistent with observed migration from the mainland, as well as a reliance on
seabird prey. These results suggest that newly-introduced breeding populations
of bald eagles on the islands will adapt to their environments based on the
available prey.
Questions to get you guys started:
1) What
is a breeding population?
2)
Is this an example of extinction or extirpation? What's the difference?
3) Why is it important to understand shifts in prehistoric or historic bald eagle diets as these populations are introduced back onto the islands?
4) Should bald eagles be reintroduced into the area?
3) Why is it important to understand shifts in prehistoric or historic bald eagle diets as these populations are introduced back onto the islands?
4) Should bald eagles be reintroduced into the area?
1)/2) A breeding population is a group of same-species individuals that freely breed within their population. The article discusses an instance of extirpation, or when a species no longer exists in a geographic region where as extinct refers to the entire disappearance of a species.
ReplyDelete3)By understanding shifts in eagle diets, you can elucidate how eagles in the prehistoric and historic past impacted the ecosystem on Channel Island both (i) without humans and (ii) after humans arrived on the islands around 13,000 years ago. Since both prehistoric and historic eagle populations occurred in their own unique environmental conditions, there is the ability to extrapolate how changes in the environment affect the diet of eagles and conversely how the eagles impacted different ecosystems in the past. This information can be used to predict what the effect of their future introduction could be.
4) Based on what was presented in the article, the introduction of bald eagles could potentially have a major impact on the Channel Island ecosystem, depending on the level of the population, specifically on the levels of currently low marine resources, seabirds, and island foxes. I think areas other than the Channel Islands should be evaluated for the potential for eagle reintroduction in order to compare the potential level of impact to the Channel Islands. For instance, if there is an area with a more stable marine and/or terrestrial population, perhaps eagles should not be reintroduced to the Channel Islands and should be reintroduced in this location.
First off I want to start by saying this is definitely an example and extirpation because bald eagles still exist, they just do not have the means to reproduce in this area. The thing that I need a little more help understanding is why the pesticide is more prominent in marine life than terrestrial life and how long will it take for the marine life to contain less DDT until it no longer affects the bald eagles. I think it is also a good idea to begin reintroducing the bald eagles into the area, but only once it is safe and there is little to no DDT left in marine life and terrestrial life in order to ensure reproductivity and safety for the bald eagles.
ReplyDeleteThe bald eagles on the Channel islands show an example of extirpation because like it has been stated previously by Asia and Alycia this article talks about the extirpation seeing as how the bald eagle still exists today just not in that geographic range. It is important to see the shifts in past bald eagle diets to see if that as well as other causes led to the extirpation. Knowing the shift from marine primary diets to more terrestrial diets can give insight into how the bald eagles adapted in the past to compare on how they might adapt if they were to be reintroduced to the Channel Islands. The article stated that seabirds, which were considered a marine prey, were a large part of the bald eagles diet which changed over time due to factors like the DDT which is a good inside to see if and how bald eagles could be introduced back into that environment. However I think it could be risky to reintroduce the bald eagles due to the risk of eliminating the endangered fox species as well as the difficulty with the DDT affecting the reproductivity of the bald eagles which I think the article should’ve elaborated more on.
ReplyDeleteBy assessing both historic and prehistoric shifts in the diet of bald eagles, we gain a better understanding of the resource pools that bald eagles draw from. With respect to conservation and potential reintroduction, such an assessment would allow for us to investigate past ecological relationships and prey preferences, to determine how current conditions would impact the bald eagle and potential prey populations. Asia makes in interesting point regarding selected relocation. While I do think that this is an excellent idea, I do worry that the bald eagle population could, perhaps, migrate (to a certain extent) and have negative impacts on sensitive populations like the endangered island fox. To address Alycia’s question, I think that marine systems show increased levels of pesticides due to rainwater runoff. This would, effectively, “wash” terrestrial surfaces and deposit the pesticides into the marine systems. However, I am sure there are other factors that are responsible for this relationship as well.
ReplyDeleteThis is clearly an example of extirpation which is defined as an extinction of the species in a particular geographical location. We know that bald eagles are not extinct everywhere but they are in the Channel Islands location. In order to understand how human pesticides have impacted these populations I think that we need more information studying the diets of these bald eagles and if the inhabitation of humans and use of pesticides is a proximate or ultimate cause of why the bald eagles are not reproducing as well as if it is another variable. Some important variables to discuss would be perhaps the lack of food sources for the bald eagles living in the region. These sort of questions need to be studied further before we can make a judgement as to whether or not reintroducing bald eagles in the Channel Islands region makes sense.
ReplyDeleteA breeding population is a population of animals or organisms in which they can interbreed with one another. In bald eagles they are trying to restore the population number to increase available breeding individuals to ensure diversity within the population. As mentioned by others in this sting of comments the bald eagles of the Channel islands is an example of extirpation due to the fact that the bald eagle still persists today. I believe that it is important to understand and study shifts in prehistoric and modern diets of animals to understand our influence on animal populations, whether that be climate wise or depleting food sources. We can see that our influence on the DDT pesticide had on the eagles by eliminating a major prey source such as the seabirds. Due to this major hit the eagles breeding population number significantly decreased on the Channel islands and are now under debate for reintroduction. Although reintroduction would be a good thing for the Channel islands but taking into account the endangered foxes on the island it would be rather risky to do so.
ReplyDeleteThis exploration of the changes in diet of bald eagles is quite important. It shows that generalist have a higher change of surviving changes to their habitat, be it man made, climate, long term or short term.Should bald eagles be introduced in the Channel island, it has be tried with some result but they have found different ranges that they can occupy with ease? Perhaps the eagles there should be studied in further experimentation & contrasted with fellow bald eagles elsewhere to see diet, how they have adapted, problems they are having etc. From there using the results data from these experimentation it can be decided if bald eagles should be reintroduced to ranges they once inhabited like the Channel Islands.
ReplyDeleteI agree that more information on the effect of DDT on reproductive health would be needed in order to determine if reintroduction is a feasible option. We can guess that if bald eagle populations are reintroduced, that they will have a huge impact on an already destabilized marine ecosystem. The probability of a dearth of marine prey will most likely skew the prey source toward terrestrial animals and the likelihood of this affecting the endangered island fox population increases. Is it right to reintroduce one species at the expense of another?
ReplyDeleteDefinitely an example of extirpation rather than extinction as the eagles are not globally extinct, and breeding populations are populations that are free to reproduce amongst themselves. Interesting that DDT affects/afflicts marine ecosystems more... due to run off possibly? The reintroduction of a high tier predator into the environment should be carefully done; the rest if the ecosystem adapted to DDT, eagles did not. their reintroduction could upset the existing equilibrium. But otherwise im for it.
ReplyDeleteBald eagles being generalists allows them to live in a large range of environments and due to their ability to move freely from place to place i wonder if human intervention is necessary. at the point in which the channel islands is Habitable again for bald eagles what is stopping them from repopulating the islands on their own. on the same line of reasoning if a space in California is protected and provides an adequate habitat for these birds would they not naturally begin to appear in this area? I would not expect any adverse effect to the habitat ass generally the introduction of predators increases diversity in the area. i expect the largest source of interference may come from pet owners who may fear their pets will become prey.
ReplyDeleteThe change in diet shows that the bald eagle is resilient to changing environments. I do not believe that human involvement is necessary at this point because as we can see from the paper, they are alternating their diet based on the resources available. Bald eagles could begin to reproduce again on the Channel Islands.
ReplyDeleteA breeding population is a population where breeding is free tooccur with room for evolutionary change. This paper is an example of extirpation since bald eagles are still alive today, just not in a specific range, compared to extinction in which an entire species (across all geographical ranges) dies out. The idea of relocation (as mentioned above) does seem like a possible and beneficial idea to try and restore bald eagle population, but as Andrew said, the bald eagle could become an invasive species to the area and out-compete many of the other organisms.
ReplyDeleteQuestions to get you guys started:
ReplyDelete1) What is a breeding population?
2) Is this an example of extinction or extirpation? What's the difference?
3) Why is it important to understand shifts in prehistoric or historic bald eagle diets as these populations are introduced back onto the islands?
4) Should bald eagles be reintroduced into the area?
To answer one of the questions set forth by this weeks discussion group this is an example of extirpation, the difference between extinction and extirpation is that extinction means that there are no longer living organisms of a particular species any where in the world where extirpation is a local extinction meaning that there are no more organisms of a species in a specific geographic location but it is still extant in other areas around the world. I honestly do not think that the bald eagle should be reintroduced due to residual affects of human activities. Bald eagles were only recently (within the last 10 years) taken off the endangered species list, the paper continually talked about the residual effects from DDT use, while efforts to remove non native species were successful to bring back an ecosystem similar to that of the past, this doesn't mean they expunged the chemical residues left over from agricultural farming. While bald eagle populations are flourishing around the US, just because there were historic populations once present in an area does not mean there should be populations there curently, I think that purposely introducing these birds to the harmful leftover effects of DDT, as demonstrated by unsuccessful hatching is wrong.
I noticed that both studies followed similar methods for SIA and so several questions came to mind. We have previously discussed analyzing δ13C and δ15N values to determine what an individual ate but what is the added benefit of also looking at keratine δ13C from feathers? How is this different than just looking at the values obtained from a bone sample? Additionally, both papers mentioned feathers needed to be corrected for "both trophic and tissue-specific discrimination" how is this exactly done and why?
ReplyDelete1) A breeding population are individuals within a population that breed without human interaction.
ReplyDelete2) This paper is an example of extirpation not extinction. The difference is that extinction is the total disappearance of a species and extirpation is when the numbers of the species decrease. Since there were still some eagles left extinction had not happened.
3) It is important to understand the shifts in eagle diet when reintroducing them to see weather or not they can adapt to the resources that are currently in the environment. If eagles had only one source and of food and historically they did not eat anything else it may not be a good idea to reintroduce them since that food source could now be contaminated with DDT causing them to be unable to reproduce. However, since historically eagles can eat many different things it is a good idea to reintroduce them since they can eat things that are not contaminated with DDT and be able to reproduce again one day.
4) I do think it is a good idea to reintroduce eagles into the area since historically eagles have been able to adapt to different sources of food.
Once again humans are responsible for the extirpation of a important species. Before eagles are reintroduced into the area I really think that more research needs to be done on what exactly caused this breeding behavior. Also knowing how long this chemical remains in the environment is extremely important.
ReplyDeleteI agree with everyone that humans are the cause of extirpation. Re introducing the eagles would be important but more studies need to be done as to how they can survive in modern times.
ReplyDeleteBreeding populations are groups of individuals that are of the same species that interbreed. This would be an example of an extirpation as Bald Eagles did not become extinct globally,but rather the "extinction" a few breeding populations. It is important to understand shifts in diet of Bald Eagles in California because it could predict the diet of newly introduced breeding populations. I don't think that Bald Eagles should be reintroduced to the Islands (at least yet) because they have potential to put pressure on recovering seabird and fox populations, unless it could be determined that populations of these species were stable enough or that an alternative food source is in enough abundance to displace predation. Also, pinniped carcasses as a potential food source could pose risks of DDT contamination due to biomagnification.Though I am curious as to what the half-life is of DDT is as this bears magnitude to the timing of reintroduction.
ReplyDeleteI believe it is important to understand the baseline shift for these ecosystem especially if you are trying to reintroduce and species such as this, mostly because you need to see if that ecosystem still has enough of anything left in it to sustain said population or of there is enough then how much of what's in there and the kind of prey. These eagles shouldn't be more introduced than they are currently mostly because if we introduce them really fast back into the ecosystem it may lead to a sort of ecosystem shock and things may shift unexpectedly in the system for other species.
ReplyDelete