Reading the Signs: Seabird sensitivity to environmental change and their potential as indicator species

By: Nicole Suren, SRC Intern

As climate change has had increasingly noticeable effects on the earth, scientists have developed more accurate and innovative ways to determine what these effects mean for the natural world. One of these methods is to use indicator species, species that can be used as proxies to diagnose the health of an ecosystem, to gauge how environments are changing and what can be done to mitigate these changes. Seabirds are emerging as the best indicator species in many marine environments, and their role in predicting environmental change and determining management strategies is becoming progressively more important as their sensitivity to environmental change is putting their populations at risk more than ever before.

Birds and Climate Change

Birds experience a wide variety of climate-dependent effects on their ecology and survival, which has made them popular subjects for ecological study. Some of the factors influenced by climate include metabolic rate, breeding success, and certain behaviors such as foraging and courtship behaviors, among many other things (Crick, 2004), and as climate change has gradually invoked large changes in bird habitats, birds have also experienced changes in distribution and phenology (periodic life cycle events such as migrations and breeding). Changes in phenology can include phenological miscuing, where the birds respond inappropriately to misleading environmental cues. For example, warmer weather can cause birds to arrive at breeding grounds early, although the conditions there may not yet be optimal. They can also experience phenological disjunction, where a species comes out of synch with its environment (Crick, 2004). Continuing with the previous example, the birds may experience phenological disjunction if their preferred prey is abundant when they usually arrive, but it is not yet abundant enough to sustain the breeding populations when they arrive at the wrong time.

Seabirds in Peril

Seabirds are especially sensitive to changes brought about by climate change, as they usually experience bottom-up effects caused by an unanticipated spatial or temporal mismatch with their prey (Grémillet & Boulinier, 2009). In other words, climate change can alter the location and/or timing of prey abundance, which adversely affects seabird populations. Seabirds in Antarctic ecosystems are also particularly vulnerable to habitat loss, as many species depend on ice cover for breeding success (Younger, Emmerson, & Miller, 2016). Seabirds have three options in responding to these challenges: 1) change their trophic status/foraging behavior, 2) change their distribution, or 3) go extinct (Grémillet & Boulinier, 2009). While options one and two are sometimes possible, they are restricted due to the memory effects and social constraints of seabird populations. Seabirds have been shown to use their memories of foraging in previous years to optimize foraging in the current year, which often results in high site fidelity. If the distribution of prey suddenly changes, this strategy becomes detrimental to foraging success.

Breeding colonies can also present a variety of climate-related challenges to seabirds. First, they have been recognized as centers of information for individual seabirds. Neighboring colonies will often have their own “cultures,” meaning that all the birds from one colony will usually use the same foraging grounds. If those foraging grounds no longer have abundant prey, then the social pressures to use those grounds will also be detrimental to foraging success. Additionally, there is high site fidelity in the colonies themselves because breeding colonies take a long time to establish (Grémillet & Boulinier, 2009). The combination of these factors can cause birds to fall into “ecological traps:” habitats that are low quality for reproduction and cannot sustain a population, but are chosen over higher quality habitats (Donovan & Thompson, 2001).

Seabirds as Indicator Species

Seabirds are ideal indicator species for marine environments for several reasons. First, they are highly visible in an environment where most other organisms are hidden underwater. Most species have large, easily locatable, land-based colonies where individuals can be captured and measured, as well as followed to sea to be studied (Piatt, Sydeman, & Browman, 2007). This ease of study in combination with their high sensitivity to environmental change makes them an obvious choice to represent the biological effects of climate change for many scientists. Declines in bird populations have accurately predicted fish stock collapses in the past, such as Peruvian booby population declines preceding the collapse of the Peruvian anchovetta.

Figure 1: Peruvian boobies, the species whose population declines helped predict the collapse of the Peruvian anchovetta. Image from Wikimedia Commons.

The challenge moving forward will be to define the parameters of seabird populations that can serve to predict other types of ecological effects. So far, studies have focused on seabirds as several types of indicators. They can serve as sentinel species, where levels of contaminants in the bodies of the birds represent environmental pollution. Predictive population models are also being used to predict the future of fish stocks, and different population parameters are being refined as indicators on different time scales. For example, population size can be used over several-yearlong to decadal scales, while annual breeding success can span monthly to one-year time periods (Piatt et al., 2007).

The potential for seabirds to be used as environmental indicators is just one more reason they are integral in the world’s ecosystems. In addition to being top predators, important prey items, and living connections between distant locations, they could now help humans control a problem that could cause damage to habitats globally, which is why scientists and managers are working together to effectively study and conserve these vitally important species around the world.

Work Cited:

Crick, H. Q. P. (2004). {The} impact of climate change on birds. Ibis, 146 {(Supp, 48–56. Retrieved from

Donovan, T., & Thompson, F. (2001). Modeling the ecological trap hypothesis: a habitat and demographic analysis for migrant songbirds. Ecological Applications, 11, 871–882.

Grémillet, D., & Boulinier, T. (2009). Spatial ecology and conservation of seabirds facing global climate change: A review. Marine Ecology Progress Series, 391(2), 121–137.

Piatt, J. F., Sydeman, W. J., & Browman, H. I. (2007). Seabirds as indicators of marine ecosystems. MARINE ECOLOGY PROGRESS SERIES Mar Ecol Prog Ser, 352, 199–204.

Younger, J. L., Emmerson, L. M., & Miller, K. J. (2016). The influence of historical climate changes on Southern Ocean marine predator populations: A comparative analysis. Global Change Biology.


Sea Bird Telomeres

By Dave Lestino, SRC intern
Telomeres are located at the ends of each DNA strand. They can be thought of as the plastic tips of shoelaces, and protect the chromosome from deterioration. Although telomeres can’t measure exact chronological age, they can be used to measure individual quality. Use of telomere length, as a quality marker, is increasing as seen in handful of studies between 2004 and 2015. In most species, it has been observed that telomeres shorten overtime, and length corresponds with survival, life-span and reproductive success. In a study by Young et al. in 2016, telomere lengths were compared to quality markers, such as environmental condition, in the thick-billed murre.


Young et al. assessed individual quality through parental investment behaviors (trip rate and nest attendance), body condition and physiological stress (baseline corticosterone or CORT). Their samples came from three colonies of thick-billed murre (Uria lomvia), which is a species of long-lived seabird. They sampled 97 individuals from 3 colonies (Bogoslof, St. George and St. Paul) in the Baring Sea, each living under different environmental conditions. The colony on Bogoslof had easy access to nearby food sources, while St. George had access to distant but reliable sources and St. Paul had access to nearby but unreliable food sources. These food sources relate to good, intermediate and poor environmental conditions comparatively.

Young chose this species because murres are known to adjust time budgets as conditions in the environment change, in order to offer consistent levels of parental investment. Thus, telomere length would indicate quality indicators and not age as the underlying driver of telomere length. The authors predicted that longer telomere length would be associated with low baseline CORT, high body condition and high parental investment. They also predicted poor environmental conditions should strengthen the above relationships. Chick rearing murres were captured, weighed, sampled for blood and fitted with Cefas G5 loggers to record time, temperature and depth pressure every 2 seconds. After 3 days the birds were recaptured and skeletal measures were taken. In total 101 birds were captured, but due to some sampling errors the final analysis consisted of 97 individuals.
For telomere length and baseline CORT assays were completed on the blood samples. Parental investment was based on nest attendance and rate of foraging trips. To calculate nest attendance, they looked at what proportion of total time was spent at the colony, measured by a Cefas loggers mounted on the birds, recording temperature and depth. Temperatures reading higher than air or sea indicate incubation, while changes in incubation temperature marked the beginning and end of a foraging trip. Trip rate was then determined by dividing the number of trips by the total deployment time. Response variables (CORT, body condition, trip rate and attendance) were analyzed with linear models in the R environmental statistic program.

The results showed that under good environmental conditions CORT was higher in birds with shorter telomeres. In poor conditions however, this was not strengthened as predicted but instead was reversed. Birds with longer telomeres had higher levels of stress. This implies that under stressful conditions, such as the poor environment at St. Paul, younger birds will be stressed even with high individual quality. Older more experienced birds however can maintain moderate stress levels. Predictions that telomere length could predict parental investment were incorrect. A paper by Elliott et al. in 2015 shows that parental behaviors don’t change with age. Murres have shown to change foraging strategies depending on distance to food sources. The interaction of sex and colony for explaining attendance patterns can be seen in Fig. 3. In conclusion, the authors found that telomere length relates to stress levels with environmental factors acting as important mediators. As habitats around the world decline, these findings can hopefully help in futures studies to determine individual quality of species in degraded areas

Young RC, Barger CP, Dorresteijn I, Haussmann MF, Kitaysky AS (2016) Telomere length and environmental conditions predict stress levels but not parental investment in a long-lived seabird. 556, 251–259.

Do birds of a feather forage together?

By Asta Mail,
Marine conservation student

Imagine that you are entrusted with the duty of conserving a colony of beautiful seabirds. Your objective is to create Marine Protected Areas (MPA’s) that shelter birds from disturbances, so that they can do what they do best: eat, sleep, fly and reproduce!  How then do you decide which marine areas are the most important to protect?

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