Current Research Projects

Avian lifespans

I study life history trade-offs associated with long versus short lifespans and their relationship to environmental factors around the globe. Estimates of species lifespans serve to guide both conservation initiatives (e.g., identifying which life stages most limit population growth) and test hypotheses regarding the evolution of life history traits (e.g., testing whether clutch size and body mass predict global patterns in avian survival and longevity). To do this, I rely on banding data to generate minimum longevity records and survival rates for birds.

My recent work demonstrates the existence of a latitudinal survival gradient in many passerines around the world, supporting the view that tropical birds tend to live longer than their temperate counterparts (Scholer et al. 2020; Ecology Letters). A proximate mechanism that has been proposed to explain the latitudinal survival gradient is that temperate species have higher metabolisms, accelerating rates of senescence and leading to lower annual rates of survival. To test whether decreased energy metabolism is linked to long lifespan, I estimated survival rates in 37 species of birds in southeastern Peru and obtained measurements of their basal metabolic rates. As predicted, our findings indicate a negative association between apparent survival and energy metabolism (Scholer et al. 2019; Functional Ecology). And another piece of the puzzle falls into place!

A Citrine Warbler (Myiothlypis luteoviridis) banded and ready for release.

Birds and climate change

Global climate change constitutes a major challenge to birds and many species are predicted to shift their ranges latitudinally to track their preferred climate. In the tropics, latitudinal changes in climate are dampened, and species are predicted to seek relief by moving upslope in elevation. Tropical montane birds are therefore particularly vulnerable to climate change as they face both climate-mediated loss of habitat (generally mountains have less area at higher elevations) as well as novel biotic interactions from upslope invasion of lowland species.

As part of a collaboration with Dr. Ben Freeman at UBC, we recently documented one of the first cases of local extirpation in tropical mountaintop birds that we attribute to warming temperatures along the Andes mountains (Freeman et al. 2018; PNAS see the press release here). Changes in climate also affect the timing of life history events, such as breeding, molt, and migration. For instance, species of soaring birds can either delay autumn migration if conditions allow for additional breeding opportunities, or depart earlier in cases where their spring arrival has also advanced (Scholer et al. 2016; Ardea).

A montane bird species common to southeastern Peru, Yellow-throated Tanager (Iridosornis analis).

Molt

Molt is the process by which birds replace their feathers. It is an energetically costly event, but one that is required to maintain plumage and its many functions including attracting mates, thermoregulation, and keeping birds aloft while in flight. No other event occurs with such regularity throughout a bird’s annual cycle. My research on bird molt aims to address two main questions: (1) when does molt occur during the annual cycle, and (2) how does molt and the resulting plumages vary within species. Analysis of the timing of molt helps us understand how birds fit this demanding activity in with the rest of their busy schedule, such as breeding or migration, while understanding molt patterns and resulting plumages provides us with clues as to a bird's age and sex. Information on the age and sex of birds can also help refine models of demographic processes.

Most of my work has focused on developing sexing and aging criteria for Neotropical birds. We have described molt for several species of high elevation birds from southeastern Peru (Kennedy et al. 2018; Ornitología Neotropical), as well as manakins from humid and lowland tropical forests adjacent to the Manu National Park (Scholer et al. 2021, Wilson Journal of Ornithology). You can see my photos of bird molt in the photo gallery. Have an interesting bird molt photo you’d like to share? I’d be excited to check it out so please contact me.

A molt limit in the greater coverts of an Andean Solitaire (Myadestes ralloides). The outer buff-tipped feathers are retained from the juvenile plumage, while the inner replaced feathers are freshly molted. This indicates the bird has completed its formative molt and is likely around 3 to 6 months of age.

Spatial modeling

Habitat type and structure, the presence or absence of another species, and historical events can all play a role in sculpting species distributions. I use spatial modeling to describe and predict where species occur across the landscape. Often times, the goal of these projects is to help inform species management and conservation. For instance, modeling habitat suitability for owls of conservation concern in Idaho’s Boise National Forest (Scholer et al. 2014; Journal of Raptor Research) or predicting nesting habitat in managed pine plantations for New Zealand Falcon. In both cases, the end product is a spatially explicit map of species occurrence, which provides land managers with a tool to guide practices on where and when to harvest trees and help set targets for restorations of species habitats and populations. I am also interested in understanding how species interactions maintain species range limits in both temperate (Scholer et al. 2018; Avian Conservation and Ecology) and tropical forests.

A patch work of cut and mature forest in a pine plantation in New Zealand. These forests are a favorite nesting spot for the Karearea or New Zealand Falcon (Falco novaeseelandiae)

You can follow updates of my most current research for any of these topics on my research gate profile here.