territory densities early in 2014

If you are a Grasshopper Sparrow, deciding where to defend a territory in a huge area of beautiful, perfect grassland habitat, why would you decide to stick close to other territorial males? This seemingly simple question still doesn’t have an answer, despite it being one of the first questions we tackled when initiating research at the Konza Prairie. We now have a good idea of what DOESN’T drive patterns of aggregation, however!


In 2013, Steffanie Munguia tackled this as her REU project, experimentally testing the prediction that aggregation functions to minimize the costs of nest predation and brood parasitism. But we saw no difference between birds in aggregated vs. isolated territories. The next summer, Sarah Winnicki followed up in her REU project where Steffanie left off. This project eventually involved testing predictions of every hypothesis we could come up with, yet the data are consistent with none of the alternatives. Read this paper (Winnicki_etal_2020_Ecology) and learn why and how social and genetic mechanisms cannot explain aggregation! Our best guess is that population declines and/or the massive changes the Great Plains have experienced have affected the fitness payoffs of this behavior.

ExpandClose

Wet tropical forests harbor the highest biodiversity of any ecosystem on earth. They are also some of the most threatened. Which species are most at risk, and why are they declining?


We have used long-term citizen-science data collected at La Selva Biological Station in the Caribbean lowlands of Costa Rica to quantify rates of population change, and associate both declines and successes with species-level traits to test hypotheses regarding why some species are doing well and others are disappearing, even from intact forest. Some of these results are surprising, revealing that not only are  understory insectivores at risk (a group commonly identified as being particularly susceptible to fragmentation), but small-bodied birds of all dietary guilds are declining. These results suggest that physiological and energetic constraints along with climatic conditions may be more important than commonly appreciated in driving declines.

Alice has also collaborated with multiple other researchers working in the same region to synthesize evidence in support of alternative explanations for population change in this region.

ExpandClose

Birds of high elevations face unique challenges that has shaped their evolutionary ecology, and will influence their persistence in future decades.


Our research on this topic grew out of interest on the selective forces that lead to altitudinal migration behavior in tropical and temperate birds, as well as in bats. In collaboration with Kathy Martin at UBC, we’ve found that high-elevation living has predictable consequences for life histories, with high elevation populations having lower fecundity, but not consistently higher survival than their lower-elevation counterparts. Additionally, around the globe, high-elevation populations have shorter breeding seasons which, in temperate areas in intuitive, but at low latitudes, is intriguing.

High elevation bird communities in British Columbia are also surprisingly diverse, and alpine areas are under-appreciated and potentially critical stop-over areas during fall migration for high-latitude breeding birds of multiple guilds.

ExpandClose

Tree Swallows nest in boxes. That simple fact makes them ideal subjects for studies examining reproductive behavior and the consequences of individual-level traits on fitness.


Alice collaborated with Dave Winkler at Cornell as a post-doc to address three questions: (1) What are the consequences of individual variation in timing of arrival to breeding sites following spring migration? (2) Why do females lose weight during reproduction? and (3) How, exactly, do chicks die during bouts of bad weather? Two of these projects are, unfortunately, still in the file cabinet (guilt!). The answer to the mass loss question is fascinating… females actively modulate body composition throughout the nesting period in ways that balance risk of starvation if bad weather hits during incubation, and the costs of aerial foraging once chicks hatch.

ExpandClose

Alice’s dissertation research and portions of her post-doc tested multiple alternative hypotheses to explain why some, but not all, tropical birds (especially those dependent upon fruits) regularly engage in predictable, seasonal migrations from higher-elevation breeding sites to lower-elevations during the non-breeding season.


This body of research has resulted in numerous publications and one of the most comprehensive set of studies of the ultimate factors shaping migration behavior in wild birds. Much of that work was conducted along a protected gradient of wet forest from La Selva Biological Station in the lowlands, up through Braulio Carrillo National Park and several adjoining private reserves. Alice conducted a great deal of the breeding-season research at Rara Avis reserve, an incredibly beautiful and incredibly wet forest at about 750 m elevation.

A few of the key take-home messages include the following: (a) simple variation in food availability does not drive downhill migration in this system; (b) reductions in foraging time due to heavy rain likely DO drive downhill movements, and which species or individuals migrate depends on traits that influence energetic needs; (c) while migration may increase the chances of surviving during the non-breeding season, it has carry-over effects to the breeding season with migrants having lower chances of reproducing.

There have been many associated papers and side-projects related to this topic, including work that takes the plants’ point-of-view, studying phenological strategies and fruit removal rates in this seed dispersal mutualism.

ExpandClose

We know that animals select habitat at multiple spatial scales, but typically, we try to understand why we find animals in some but not all locations by only measuring attributes of territories and home ranges. How important is the landscape context? and what features do some of the most threatened birds of tallgrass prairies respond to?


This project was the focus on Mark Herse’s MS thesis. We found that even in the Flint Hills of Eastern Kansas where the last large tracts of prairie remain, Henslow’s Sparrows are extremely rare, move around within breeding seasons, and select habitat at far larger spatial scales than that of their territories. Rather surprisingly, when they arrive in spring, they settle disproportionately frequently in Conservation Reserve Program (CRP) fields, a habitat typically regarded as low-quality compared to native prairie. This is likely due to the prevalence of prescribed spring fires to increase forage quality for cattle. As the season progresses, they move to sites surrounded by large expanses of native prairie (Herse et al. 2017, Landscape Ecology).

Capitalizing on the astounding number of point-count surveys conducted for the Henslow’s Sparrow project, we were able to use abundance data from the much more common Grasshopper Sparrow to test long-standing ideas about the relative importance of habitat area, and the configuration of habitat patches. Mark devised a novel way to distinguish these analytically, and found that indeed, the amount of ‘core’ habitat (grassland area at least 60 m from edges) was a far better predictor of abundance in this species (Herse et al. 2018, JAppliedEcol).

Finally, using data from four declining species, we determined the landscape contexts in which fragmentation effects are strongest for grassland birds. Because most of these species are apparently not at all dispersal-limited, fragmentation effects may be quite different in prairies as compared to forested ecosystems. The final paper in this series was published in Landscape Ecology in 2020.

ExpandClose