The hunger games: Do fledged chicks beg honestly?

Blog written by Kayla Davis. Read the full paper here.

Imagine you are a newly fledged tern chick, bright-eyed and ready to take on the skies with your freshly grown feathers. There’s a problem though; catching fish is hard, and you always seem to be hungry because you are still growing! Luckily, your dad (or mom, if you were hatched second) is by your side at the breeding colony and during pre-migratory staging to make sure you stay healthy and strong by feeding you tasty sand eels. However, as with most growing youths, the relationship between parents and offspring changes as offspring grow and gain independence. Do you try to maximize parental care from your dad or mom by begging dishonestly? Or are you an honest tern chick that only begs when you need to be fed?

Honest signaling theory seeks to explain animal communication and interactions by describing signals as “honest”, meaning that the sender displays a reliable signal, or “dishonest”, meaning that the sender gives false information to the receiver of the signal. Theory states that costs imposed on creating signals should function to maintain honest signaling mechanisms. However, in the case of begging, especially for nearly adult-sized fledglings, this behavior may not be particularly costly. There is a long history of research on begging behavior as an honest signaling mechanism in birds, but most of this work has focused on nestlings. Parent-offspring communication is expected to change as offspring gain the functional independence needed to survive on their own, and the costs and benefits of behaving honestly or dishonestly are also likely to change during this time.

In our study, we conducted behavioral observations of roseate tern fledglings during the post-breeding, pre-migratory staging period at Cape Cod National Seashore, Massachusetts, USA to investigate the honesty of parent-offspring interactions during the postfledging period. Roseate terns are unique in that most of the northwest Atlantic breeding population departs the breeding colonies (Nova Scotia, CA to Connecticut, USA) after chicks have fledged to stage for several weeks on beaches and islands around Cape Cod, Massachusetts. While there, roseate tern fledglings continue to depend on their care-giving parent for food as they continue to grow and build fat reserves for fall migration to South America. This unique staging strategy gave us the opportunity to observe post-fledging parent-offspring interactions, including lots of begging behavior.

Roseate tern chick banded with a plastic field-readable leg band. Colony managers across the entire northwest Atlantic breeding range banded tern chicks with uniquely-identifiable leg bands.

We located tern flocks at the Cape Cod staging grounds and conducted focal sampling of uniquely-marked roseate tern fledglings to quantify begging behavior as it related to date of the staging season and time of day. We expected tern fledglings to gain independence from their parents and improve their fishing skills over the course of the staging season, so we predicted that begging behavior would decrease with date of the staging season if begging was an honest signal of need. We also predicted that begging would increase with time of day if begging was an honest signal of need because roseate terns do not fish during the night, and dusk would be the last time fledgling terns could be fed before nightfall. Thus, we expected fledgling need, and therefore begging behavior, to be highest at the end of the day before a night-time fast.

We also were interested in identifying whether young terns begged at non-parents. In colonially breeding species like roseate terns, offspring may deceitfully beg at non-parents to try to receive extra-parental care. Based on previous work on parent-offspring recognition and discrimination, we expected that non-parents would be able to discriminate their offspring from the offspring of others and would therefore not be fooled by deceitful begging. Thus, we predicted that the lack of benefits to be gained from begging deceitfully at non-parents would result in honesty of parent-offspring interactions.

Juvenile roseate tern begging at an adult. Photo credit: David Hollie.

Our predictions about begging as an honest signaling mechanism were upheld. Roseate tern fledglings begged at their parents more than non-parents, but they did not always beg at true parents. Recent conceptual studies have shown that partial honesty, particularly if the signal is low cost to produce, may be an evolutionary stable strategy. It is likely that begging is a low-cost behavior for tern fledglings, so begging at non-parents may have more potential benefits than costs, even if non-parents are rarely fooled and begging at them often does not result in feeding. The relative lack of benefits to be gained from begging at non-parents has likely resulted in mostly honest communication between tern fledglings and adults; however, the low cost of this behavior may keep deceitful begging present at low frequency because the possible benefits of extra-parental care outweigh the low cost of deceitful begging.

Relationship between begging behavior and date of staging season. As the staging season progressed, juvenile roseate terns begged at parents less frequently, but they continued to beg throughout the staging season.

Begging behavior increased with time of day as would be expected if fledgling needs were highest before nightfall and further supports our finding of honest communication between parents and offspring. We also found that begging behavior decreased throughout the staging period. However, tern fledglings continued to beg at their parents even at the end of the staging period, albeit at reduced frequency relative to the beginning of the staging season. This may be evidence to suggest that parental care continues past the staging period into migration and possibly the wintering period. If this is true, begging behavior may function as more than a signal to indicate need; it could also function to reinforce the parent-offspring bond prior to migratory departure from staging areas.

Essential waters: young bull sharks in Fiji’s largest riverine system

Written by Kerstin Glaus. Read the full article here.

The bull shark (Figure 1) is one of the few sharks that can freely swim between fresh, -and saltwater environments. Although the bull shark occurs pantropically, there is a large knowledge gap in their distribution and habitat use patterns of neonate, young-of-the-year (YOY) and juvenile bull sharks between regions. So far, such information has been gathered primarily in the northern Gulf of Mexico, in Florida and on the east coast of Australia. According to previous studies, young age classes of bull sharks occupy environmentally heterogeneous habitat and age-associated habitat transitions have been documented with YOY bull sharks occupying locations with lower mean salinities than juveniles, while sub-adults were more abundant in nearshore marine areas. Within coastal environments, juvenile bull sharks reportedly have an affinity for mesohaline areas. However, even within the same species, such habitat requirements can differ between and across regions and alter due to changing environments. To date, distribution and habitat use patterns of young bull sharks, are largely lacking from historically data-poor regions such as the South Pacific.

South Pacific Islands are among the least known or understood regions in the world. This lack of knowledge is highlighted by the fact that two aggregation sites for the young of several shark species have been discovered in just the last three years. Fiji is the South Pacific’s economic center. The archipelago consists of more than 330 islands, but the vast majority of the population inhabits the two main islands Viti Levu and Vanua Levu. Located off Viti Levu’s south coast, adult bull sharks can be studied year-round in the Shark Reef Marine Reserve (SRMR), the country’s first national marine park. Contrastingly, the exact location of essential habitats for young bull sharks and associated environmental parameters are either only preliminary investigated or virtually unknown. As a result, we have little data about essential fish habitats (EFH) for young age classes of bull sharks in Fiji.

Figure 1: A bull shark (Carcharhinus leucas) photographed in Fiji’s Shark Reef Marine Reserve. Copyright Valerie Taylor

To bridge this knowledge gap, a team of four researchers started a two-year vessel based survey in the Rewa River to the east, the Navua River to the south and the Sigatoka River to the west of Viti Levu (Figure 2). We aimed to confirm the occurrence of young bull sharks in several riverine systems, to determine their distribution and abundance in the rivers, and to collect environmental parameters at capture sites.

Our surveys usually started at low tide and typically lasted between two to six hours per day depending on weather conditions. We placed captured bull sharks in an on-board tank filled with river water (Figure 3). The following parameters were recorded for each individual caught: total straight length (Figure 4), umbilical scar condition (open, semi-healed, healed), and sex. Also, captured bull sharks were tagged with an internal Passive Integrated Transponder below the first dorsal fin for individual identification (Figure 3) prior to release (Figure 5,6). In addition, using a water quality meter, surface and bottom water temperature, dissolved oxygen and salinity were recorded at the respective sampling locations in the Rewa and Sigatoka Rivers at the beginning and end of each fishing survey.

Figure 2: The Rewa, Sigatoka and Navua Rivers in southern Viti Levu. Dashed inlets denote the stretches that were sampled
Figure 3: A neonate bull shark captured in the Rewa River, placed in an on-board tank filled with river water. The specimen is tagged with an internal Passive Integrated Transponder below the first dorsal fin for individual identification
Figure 4: A neonate bull shark captured in the Sigatoka River and placed on a board for total straight length measurement.
Figure 5, 6: Bull sharks are released after length measurement, sex determination, PIT tagging and assessment of the umbilical scar conditions. The whole procedure does not take more than 40-70 seconds.

After more than two years of extensive sampling, we captured 159 neonate and YOY bull sharks in the Rewa River and are now able to show that the Rewa River may be a hot-spot for the study of neonate bull sharks in Fiji. The study covers the first multi-year assessment of young bull shark’s occurrence and distribution across several rivers in a Pacific Island Country. Also, we examined and compared environmental conditions of two rivers, showing that the environmental profile with the highest bull shark abundance in the Rewa River typically was oligohaline and that young bull sharks are more likely to occur in the Rewa than in the Sigatoka River.

The poor knowledge of population trends in bull sharks in this unique upwelling region, together with habitat alterations and an increasing local demand for shark products for domestic consumption may lead to a potential decline of some age-classes of different elasmobranch species that may go unnoticed. Our data helps us to learn more about the bull shark’s distribution and abundance, information that is essential for studies of the species life-cycle. These new insights can provide a foundation for the urgently required assessments of essential shark habitats within the South Pacific.

Vertebrate invasions don’t seem to conform to the norm

Blog written by Marcus Lashley. Read the full article here.

Biological invasions are one of the biggest threats to biodiversity globally. Because of the pervasive threat invasions pose, understanding basic principles of invasion and how those invasions affect biodiversity is of primary interest to ecologist and conservationist. A fundamental scale-dependent relationship has been observed repeatedly across plant and invertebrate invasions. That is, invasion commonly suppresses biodiversity at small or local scales but as the spatial scale considered increases, biodiversity is either not affected or facilitated at large scales. This could happen for several reasons but most commonly, invaders regulate the dominance of a native species which can release other species in the same community ultimately resulting in the scale-dependent pattern. The scale-dependent pattern has been generalized to include vertebrate invasions but because they are often more difficult to study, to our knowledge the scale-dependence hypothesis has not been explicitly tested in a vertebrate system.

There are three basic requirements to test the hypothesis: 1) a vertebrate invasion, 2) an estimate of biodiversity with and without the vertebrate invader, and 3) an estimate of biodiversity with and without the invader across spatial scales. In the United States, one of the most problematic nonnative vertebrates is the feral pig (Sus scrofa). Feral pigs are problematic because of their foraging behavior and their taste for agricultural crops. Interestingly, in agroecosystems, land clearing often results in fragmentation of forests leaving relatively isolated forest fragments similar in composition but varying in size. Feral pigs use those forest fragments for cover while not foraging on surrounding crop fields. Thus, an agroecosystem where feral pigs have invaded may provide all three basic needs to test the scale dependence hypothesis if forest fragments have a predictable species-area relationship.

Feral pig (Sus scrofa)

We established camera traps in 36 forest fragments ranging across four orders of magnitude in area to estimate species richness of forest fragments. With camera traps, we knew many species would not be detected, however, it is common to take a subset of biodiversity in these types of studies given it is nearly impossible to tally all species present. In all, we detected 41 species, including feral pigs in 11 of the forest fragments. We took the 25 forest fragments without feral pigs and ran a simple linear model to determine that the number of species detected was very well predicted by the area of the forest fragment. The number of species detected increased as the forest fragment area increased. In other words, based on the area of a forest fragment, we can accurately predict how many species should be detected. Using that species-area relationship as a basis for how many species should be detected in a forest fragment of a given area, we then used a similar model to evaluate the number of species detected in forest fragments where feral pigs had invaded. If feral pigs are negatively affecting species richness in a scale dependent pattern, we should expect the predicted species richness across scale to have two basic properties as it relates to uninvaded fragments: 1) the y-intercept of the line should be lower than in the uninvaded estimate and 2) the slopes of the lines should not be parallel. Indeed, in forest fragments where feral pigs had invaded the y-intercept was 26% lower indicating we detected 26% fewer species than should have been expected given the fragment area. The slopes of the two lines were parallel indicating this reduced species richness occurred across the range in forest fragment size when pigs had invaded.  Collectively, those results do not support the scale dependence hypothesis in this vertebrate invasion calling into question how generalizable the scale dependence hypothesis is to vertebrate invasions.

Log–Log relationship between species richness and forest fragment area in the Mississippi Alluvial Valley invaded (solid line and solid points) and absent (broken line and hollow points) of feral swine.

In this study, we did not establish causation, so it would not be appropriate to assume that feral pigs cause the reduction in biodiversity. However, our observations are similar to other causative studies which show invasions reduce diversity by 19-27%. Moreover, feral pigs are competitors and predators of many of the native wildlife in this ecosystem, so it is plausible that they do suppress biodiversity through those mechanisms. Ultimately, more research is needed to determine if feral pigs are causing this reduction in biodiversity and to determine if the lack of scale dependence applies to other vertebrate invasions.

Changing sea-ice affects diet of Arctic sea-birds

Blog written by Mark Mallory. Read the full paper here.

The imposing cliffs of Prince Leopold Island rise sheer from Lancaster Sound and the Northwest Passage in the Canadian high Arctic.  Thick-billed murres (Brunnich’s guillemot in Europe – Uria lomvia) and black-legged kittiwakes (Rissa tridactlya) nest in the tens of thousands along the steep northeast cliffs, with glaucous gulls (Larus hyperboreus) nesting on rock towers and promontories, overlooking their prey. Thousands of northern fulmars (Fulmarus glacialis) nest around the perimeter of the island, typically near the top of the cliffs, while a few thousand black guillemots (Cepphus grylle) nest in scree and crevices, particularly on the southern side of the island. Polar bears (Ursus maritimus) often roam the beaches below the birds, while narwhal (Monodon monoceros), beluga (Delphinapterus leucas), bowhead whale (Balaena mysticetus), walrus (Odobenus rosmarus), harp seal (Phoca groenlandicus), bearded seal (Erignathus barbatus) and ringed seal (Pusa hispida) all move among the landfast ice and pack ice that forms around the deep water edges of the island.

When birds return to the island each year to breed (first the fulmars and gulls, and then later the murres, guillemots and kittiwakes), they are met with differing conditions of sea ice cover in Lancaster Sound. Some years the ice is extensive and solid, effectively blocking access to open water (necessary for feeding) up to 200 km to the east, while in other years, the water is mostly open, or in loose pack ice, through the Sound and as far west as Resolute Bay.

In earlier studies, we showed that the breeding success of the birds varies considerably with annual sea ice conditions: they do well in years with moderate to little ice cover, but both effort and success are lower in late, extensive ice years (Gaston et al. 2005. Ecography 28:331-344). We think that heavy and solid ice cover does two things: a) it delays the pulse of productivity in the ocean, meaning food supplies are late and less abundant; and b) it forces the birds to fly much farther to feed, meaning they spend more energy. Some birds in relatively poor condition may just defer breeding or abandon part way through under those conditions.

In addition to monitoring breeding, we have tracked contamination of the Arctic marine food web since 1975, using eggs from seabirds at this colony (Braune et al. 2019. Science of the Total Environment 646:551-563). Getting these data is no easy feat! After consultations with the nearby community (Resolute Bay), and usually bringing an Inuit field assistant or student trainee, we fly to the island by helicopter or Twin Otter, and if we are working on all 5 species, we set up a camp on top of the cliffs for anywhere from a week to 2 months. If we are just doing the annual monitoring of murres and fulmars, we fly down for a long, jam-packed single day of work. Once at the colony, we set up anchors and descend the 330m cliffs on 11 mm static safety ropes to breeding ledges that don’t offer too much footing. We usually do the collections around the first week of July, taking only 1 egg from selected nests, which means that some birds will lay a new egg to replace the one we’ve taken, although for 15 fulmars, we’ve robbed their breeding efforts that year (hopefully a small sacrifice for the greater good!).

That continuing story has shown that some contaminants have declined markedly since the 1970s (e.g. DDT, PCBs), others increased for a period and now seem to be plateaued (e.g., mercury), and yet others may be increasing now (various new “emerging contaminants”). While studying the contaminants of the birds, we also recorded the trophic level (i.e. where in the food web) they fed at by analyzing stable isotopes of nitrogen and carbon (as a possible correction to changes in contaminant loads). Then it dawned on us: I wonder if the trophic level of the birds differed with ice conditions, or has changed through time? That’s what precipitated our recent study.

Looking back at our data through time, and with the availability of satellite-derived information on ice cover over the years, we linked the dietary information from the isotopes to the sea ice cover conditions during egg-formation for the species. That told us that indicators of diet (i.e., isotopes) changed across the seabird community depending on sea ice conditions. During a year of particularly heavy ice cover, most species tended to forage on a less diverse array of foods, and in general the breadth of what the entire community was feeding on was smaller. We interpreted this to mean that heavy ice reduced what was available to the birds, or perhaps forced birds to eat what was more prevalent around the ice. In contrast, under minimal sea ice cover, species had more different diets from each other, and within species they were more varied. We think this may mean that individual specializations are expressed more under these environmental conditions.

However, the big point we found was that we really only saw substantial changes in seabird diet and environmental conditions when we considered the whole community at the island, and we think that in the future, efforts to determine the effects of stress from a more unpredictable climate will be best assessed by looking at communities and multiple species.

We can tell a lot from a seabird egg, and if timed right, we can get this information without having much negative effect on a colony. Eggs from Arctic seabirds continue to divulge secrets about threats to the Arctic environment, and how seabirds respond to those stressors.

Peer-reviewed articles on the important, everyday components of our work lives

Blog written by Meghan Duffy, Associate Editor for Academic Practice in Ecology and Evolution

A few years ago, I did a study of last and corresponding authorship practices in ecology. I thought the results were interesting and might be useful to others, so started to think about writing it up for publication. But, when I did, I realized I had a problem: I wanted the paper to be seen by ecologists, but I wasn’t sure of what ecology journal might be willing to publish such a piece.

It turns out I wasn’t alone in feeling like we needed a venue for this sort of study in a journal that focuses on ecology and evolution. Many ecologists and evolutionary biologists are in positions where much of their time is spent in teaching and service roles. Even research intensive positions often involve leading teams, writing grants, sitting on review panels, and networking. Thus, while much of our training focuses on how to carry out our own research, many of us are in positions where we need to do so much more than that. And we need ways to learn and reflect on the skills and concepts that deal with these other aspects of our scientific lives.

When the Academic Practice section was announced in 2017, the call noted:

“As ecologists and evolutionary biologists, we apply scholarly approaches to the myriad roles we have undertaken in our professions. Publishing about such new knowledge and advances in our ‘roles’ (e.g., teaching, service, outreach, professional development, and change) typically occurs in a range of transdisciplinary journals. Tracking down this literature, in what can be disparate fields of research, is time‐consuming and can prevent groundbreaking ideas from being more generally acknowledged and ultimately implemented in the day‐to‐day.

Our new category “Academic Practice” is intended to remedy this situation and bring high‐quality studies … to the attention of our readers.”

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In the end, my paper was the first official “Academic Practice in Ecology & Evolution” paper published by Ecology & Evolution, though the journal had already published a few articles along these lines prior to this official call (this paper by Fox & Burns was published in 2015 and this Fox et al. paper was published in 2016). I now am the Associate Editor who handles the Academic Practice submissions. You can now identify a paper as suitable for this section upon submission, which leads it into a system where Jennifer Firn is assigned as the Editor and me as the Associate Editor. When reading the submissions, I often think of how they are like really interesting, data driven blog posts that I would read anyway. So, in this post, I wanted to briefly highlight five recent publications in this section (selected with help from Jennifer!) which cover topics from grant writing to teaching to how we actually do our science to publishing to mentoring:

    • Teaching: Farrell & Carey wrote about activities aimed at developing computational literacy that they incorporated into undergraduate ecology courses, arguing that such training is important but currently lacking in the undergraduate ecology curriculum. They found that two modules that teach students how to analyze large scale datasets and to carry out simulation modeling led to students reporting significantly increased proficiency and confidence in their use of Excel and R and in computer programming in general, though did not significantly impact students self-reported likelihood of using Excel, R, or computer programming.
  • Research: Craven et al. analyzed changes in the interdisciplinarity of biodiversity science, analyzing almost 100,000 papers published over a 20 year period. They found that concept and subdiscipline diversity in biodiversity science have decreased over time, arguing that this reflects consolidation of the discipline around core concepts.
  • Publishing: Paine & Fox analyzed the effectiveness of journals as arbiters of scientific impact, using a survey of over 12,000 authors and data on almost 17,000 rounds of manuscript submission. This study has a wealth of really interesting results, including finding that ~65% of manuscripts were published in the first journal to which they were submitted (this surprised me!) and that, for those manuscripts that were rejected, 78% of were submitted to a journal with a lower impact factor. Based on the number of citations that a manuscript received after publication compared to the journals that rejected it, the authors concluded that the peer review system is an effective judge of the likely impact of a paper.
    • Grant writing: In contrast to Paine & Fox’s conclusion that journals (and peer review) are effective at judging likely impact, Roger Cousens argues that grant allocation systems are highly influenced by chance, and then goes on to present his personal conclusions regarding the factors that contribute to variation in the assessment of grant proposals, as well as his suggestions of things we could change. He argues against a lottery system (arguing that this would lead to less well-developed projects), and for grant agencies being more clear about their expectations.
  • Mentoring: Mentorship is such an important part of many of our jobs, but also something we receive very little formal training in. Thus, it didn’t surprise me to see this paper by Hund et al. zipping around social media when it first came out! They explain why good mentoring is so important, some of the unique challenges associated with mentoring in academia, and talk about a course that they developed and taught at the University of Colorado that focused on mentoring.

I was recently at a day-long event at Michigan that focused on discipline-based education research (DBER). At it, people kept saying that they struggle with where to publish this work — if they want to influence practice, it makes sense to publish in disciplinary journals, but often disciplinary journals don’t accept these kinds of articles. It reminded me that we are lucky to have a forum for articles about all of those parts of our day-to-day work lives.

Many of the articles that have been published in the Academic Practice section are now spotlighted here; that spotlight will be updated periodically. If you have questions about a potential submission, please don’t hesitate to reach out to me or Jennifer!

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