Jared D. Wolfe

Decay of interspecific avian flock networks along a disturbance gradient in Amazonia

Our understanding of how anthropogenic habitat change shapes species interactions is in its infancy. This is in large part because analytical approaches such as network theory have only recently been applied to characterize complex community dynamics. Network models are a powerful tool for quantifying how ecological interactions are affected by habitat modification because they provide metrics that quantify community structure and function. Here, we examine how large-scale habitat alteration has affected ecological interactions among mixed-species flocking birds in Amazonian rainforest. These flocks provide a model system for investigating how habitat heterogeneity influences non-trophic interactions and the subsequent social structure of forest-dependent mixed-species bird flocks. We analyse 21 flock interaction networks throughout a mosaic of primary forest, fragments of varying sizes and secondary forest (SF) at the Biological Dynamics of Forest Fragments Project in central Amazonian Brazil. Habitat type had a strong effect on network structure at the levels of both species and flock. Frequency of associations among species, as summarized by weighted degree, declined with increasing levels of forest fragmentation and SF. At the flock level, clustering coefficients and overall attendance positively correlated with mean vegetation height, indicating a strong effect of habitat structure on flock cohesion and stability. Prior research has shown that trophic interactions are often resilient to large-scale changes in habitat structure because species are ecologically redundant. By contrast, our results suggest that behavioural interactions and the structure of non-trophic networks are highly sensitive to environmental change. Thus, a more nuanced, system-by-system approach may be needed when thinking about the resiliency of ecological networks.

Correlations between El Niño—Southern Oscillation and Changes in Nearctic—Neotropic Migrant Condition in Central America

ABSTRACT. Climatic changes induced by the El Niño—Southern Oscillation (ENSO) commonly influence biological systems; however, climatic variability and multitrophic interactions within tropical latitudes remain poorly understood. We examined relationships between migrant condition and ENSO during spring migration in Costa Rica. Our study is based on correlating an ENSO index with body-condition metrics of six Nearctic—Neotropic migrant bird species during stopover in Costa Rica over a 10-year period. This study is the first to report correlations between El Niño and changes in condition of multiple migrant species. The condition of one insectivore improved, whereas two frugivores experienced reduced condition during El Niño. Our detected correlations suggest that the ENSO cycle may influence changes in migrant mass; such interactions may ultimately affect demographics of certain frugivorous and insectivorous migrant species. Potential future management considerations are discussed in light of global climate change and our findings.

BREEDING SEASONS, MOLT PATTERNS, AND GENDER AND AGE CRITERIA FOR SELECTED NORTHEASTERN COSTA RICAN RESIDENT LANDBIRDS

Abstract Detailed accounts of molt and breeding cycles remain elusive for the majority of resident tropical bird species. We used data derived from a museum review and 12 years of banding data to infer breeding seasonality, molt patterns, and age and gender criteria for 27 common landbird species in northeastern Costa Rica. Prealternate molts appear to be rare, only occurring in one species (Sporophila corvina), while presupplemental molts were not detected. Most of our study species (70%) symmetrically replace flight feathers during the absence of migrant birds; molting during this period may limit resource competition during an energetically taxing phase of the avian life-cycle.

Island vs. countryside biogeography: an examination of how Amazonian birds respond to forest clearing and fragmentation

Avian diversity in fragmented Amazonian landscapes depends on a balance between extinction and colonization in cleared and disturbed areas. Regenerating forest facilitates bird dispersal within degraded Amazonian landscapes and may tip the balance in favor of persistence in habitat patches. Determining the response of Amazonian birds to fragmentation may be hindered because many species use adjacent second growth matrices thereby limiting the applicability of island biogeography to predict species loss; alternatively, a countryside biogeographic framework to evaluate the value of regenerating forest may be more appropriate. Here, we used point-count and capture data to compare Amazonian bird communities among continuous forest, 100 ha forest fragments with adjacent second growth, young and older second growth plots, and 100 ha forested islands bounded by water, to test the applicability of island biogeography on the mainland and to assess the ecological value of a regenerating matrix. Among foraging guild...

Meta-analysis of California Spotted Owl (Strix occidentalis occidentalis) territory occupancy in the Sierra Nevada: Habitat associations and their implications for forest management

ABSTRACT We assessed the occupancy dynamics of 275 California Spotted Owl (Strix occidentalis occidentalis) territories in 4 study areas in the Sierra Nevada, California, USA, from 1993 to 2011. We used Landsat data to develop maps of canopy cover for each study area, which we then used to quantify annual territory-specific habitat covariates. We modeled the relationships between territory extinction and colonization using predictor variables of habitat, disturbance (logging, fire), climate, and elevation. We found that forests with medium (40–69%) and high (≥70%) canopy cover were the most important predictors of territory occupancy in all study areas, and that both canopy cover categories were positively correlated with occupancy. We used analysis of deviance to estimate the amount of variation explained by the habitat covariates (primarily medium and high canopy cover) and found that these covariates explained from 35% to 67% of the variation in occupancy. Climatic covariates were not correlated with occupancy dynamics and explained little of the variation in occupancy. We also conducted a post hoc analysis in which we partitioned canopy cover into 10% classes, because our original partitioning into 3 classes may have lacked sufficient resolution to identify canopy cover levels where occupancy changed abruptly. In this post hoc analysis, occupancy declined sharply when territories contained more area with <40% canopy cover, and the amount of 50–59% and 60–69% canopy cover had a more positive association with occupancy than did 40–49% canopy cover. Our results suggest that some fuels treatments intended to reduce fire risk and improve forest resilience could be located within Spotted Owl territories without adversely impacting territory occupancy if such treatments do not consistently reduce canopy cover below 50%. We suggest that future work quantify components of forest structure (e.g., large tree density, vertical complexity) known to be selected by owls and relate these characteristics to occupancy and fitness metrics.

Searching for consensus in molt terminology 11 years after Howell et al.'s “first basic problem”

ABSTRACT Howell et al. (2003) published an innovative augmentation to terminology proposed by Humphrey and Parkes (1959) that classified bird molt on the basis of perceived evolutionary relationships. Despite apparent universal applicability, Howell et al.s (2003) proposed terminological changes were met with criticism that cited a failure to verify the evolutionary relationships of molt and an inability to recognize homologous molts even within closely related taxa. Eleven years after Howell et al. (2003), we revisit arguments against a terminological system of molt based on evolutionary relationships, suggest an analytical framework to satisfactorily respond to critics, clarify terminology, and consider how to study molt variation within an evolutionary framework.

Thamnophilidae (Antbird) Molt Strategies in a Central Amazonian Rainforest

ABSTRACT Avian molt, or the regularly scheduled replacement of feathers, is an important life history event, particularly in central Amazonian rainforest birds for which a relatively high proportion of the annual cycle can be dedicated to this process. Here, we detail molt strategies of 18 antbird species (Thamnophilidae) based on 2,362 individuals captured from lowland tropical rainforest at the Biological Dynamics of Forest Fragmentation Project near Manaus, Brazil. All species exhibited a molt strategy consistent with the Complex Basic Strategy, in which birds undergo an inserted preformative molt within the first cycle, but apparently lack prealternate molts. The preformative molt and resulting formative plumage aspect of the 18 antbird species can be grouped by three distinct patterns: 1) a complete molt resulting in an adult-like formative plumage without molt limits; 2) a partial molt involving body feathers, lesser coverts, at least some or all median and greater coverts, and sometimes tertials or rectrices, resulting in an adult-like formative plumage with molt limits; and 3) a partial molt as in ‘2’ but resulting in an adult female-like formative plumage in both sexes with plumage maturation delayed in males until the second prebasic molt. In addition, we show that one species, Percnostola rufifrons, exhibited an extra inserted molt (a partial auxiliary preformative molt) in the first cycle before initiating a complete preformative molt making this, to our knowledge, the first description of an auxiliary preformative molt for a suboscine. The extent of the preformative molt or delayed plumage maturation was not predicted by ecological guild, raising questions about how phylogenetic relatedness and ecological adaptation drive variation in molt patterns across antbirds.