Small hosts infrequently disrupt laying by Brown-headed Cowbirds and Bronzed Cowbirds

ABSTRACT Brood parasites often must overcome host defenses that may include behaviors that serve other functions, such as deterrence of predators and nest attendance during laying and incubation. Host use by brood parasites may also be influenced by competitors in areas where more than one parasitic species occurs. We identified the degree to which behavior of potential hosts and potential competitors affected laying by Brown‐headed Cowbirds (Molothrus ater) and Bronzed Cowbirds (M. aeneus) at a site in south Texas where they co‐occur. We watched potential host nests during the presunrise period to record cowbird laying and document nest visitation, laying, cowbird‐host encounters, and nest attentiveness by hosts. Hosts were frequently at their nests when cowbirds laid eggs (83% of 121 watches among nests of five host species) and cowbirds regularly encountered hosts (43–74% and 40–77% of watches per species of host for Brown‐headed and Bronzed cowbirds, respectively). Host nest defense infrequently interfered with cowbird laying and cowbirds rarely interacted with one another during laying. Overall, 12% of the 42 cowbird laying attempts that elicited host nest defense failed, resulting in cowbird eggs either laid atop hosts as they sat in nests or laid outside the nest cup. We clearly documented that relatively small hosts can thwart parasitism by cowbirds. Thus, the potential for successful defense of nests should be considered when assessing the evolution of behaviors to deter the removal of host eggs by cowbirds and mechanisms leading to nest abandonment. Regarding the latter, the presence of a cowbird at a nest would be a poor indicator for parasitism as some laying attempts were thwarted and unparasitized broods were reared at those nests. Despite the potential for nest defense to affect host use by cowbirds, we did not detect an effect of nest defense. Because most host defense was ineffective, we examined hypotheses for the timing of cowbird laying and host nest attendance. Our analysis of time of day of laying by Brown‐headed Cowbirds at our site and data compiled from the literature suggests that laying time is best predicted by the time of civil twilight (first light) rather than sunrise.     

Hosts feeding only Brown‐headed Cowbird fledglings: where are the host fledglings?

ABSTRACT.   Brown-headed Cowbirds ( Molothrus ater ) impose costs on their hosts, usually resulting in fewer or no host young being raised. In 95% of the studies where attempts were made to estimate the cost of parasitism, cost was measured as the difference in host nestling survival in parasitized and unparasitized nests. For hosts that fledge at least some of their own young along with cowbirds, the magnitude of further brood reduction beyond the nestling stage is not known. To examine the possibility that further brood reduction occurs during the fledgling stage, we compiled 102 observations of 45 species feeding fledgling cowbirds. In 97 cases, observers did not record hosts feeding their own young, suggesting that many young die shortly after fledging from parasitized nests. These observations suggest that measuring the cost of parasitism as the difference between the number of host young fledged from parasitized and unparasitized nests probably overestimates the reproductive output of many hosts. If costs increase during the fledgling stage, then the costs of brood parasitism have been underestimated in many studies.     

Seed Menus: An integrated decision‐support framework for native plant restoration in the Mojave Desert

The combination of ecosystem stressors, rapid climate change, and increasing landscape‐scale development has necessitated active restoration across large tracts of disturbed habitats in the arid southwestern United States. In this context, programmatic directives such as the National Seed Strategy for Rehabilitation and Restoration have increasingly emphasized improved restoration practices that promote resilient, diverse plant communities, and enhance native seed reserves. While decision‐support tools have been implemented to support genetic diversity by guiding seed transfer decisions based on patterns in local adaptation, less emphasis has been placed on identifying priority seed mixes composed of native species assemblages. Well‐designed seed mixes can provide foundational ecosystem services including resilience to disturbance, resistance to invasive species, plant canopy structure to facilitate natural seedling recruitment, and habitat to support wildlife and pollinator communities. Drawing from a newly developed dataset of species distribution models for priority native plant taxa in the Mojave Desert, we created a novel decision support tool by pairing spatial predictions of species habitat with a database of key species traits including life history, flowering characteristics, pollinator relationships, and propagation methods. This publicly available web application, Mojave Seed Menus, helps restoration practitioners generate customized seed mixes for native plant restoration in the Mojave Desert based on project locations. Our application forms part of an integrated Mojave Desert restoration program designed to help practitioners identify species to include in local seed mixes and nursery stock development while accounting for local adaptation by identifying appropriate seed source locations from key restoration species.     

A standard protocol for reporting species distribution models

Species distribution models (SDMs) constitute the most common class of models across ecology, evolution and conservation. The advent of ready-to-use software packages and increasing availability of digital geoinformation have considerably assisted the application of SDMs in the past decade, greatly enabling their broader use for informing conservation and management, and for quantifying impacts from global change. However, models must be fit for purpose, with all important aspects of their development and applications properly considered. Despite the widespread use of SDMs, standardisation and documentation of modelling protocols remain limited, which makes it hard to assess whether development steps are appropriate for end use. To address these issues, we propose a standard protocol for reporting SDMs, with an emphasis on describing how a study's objective is achieved through a series of modeling decisions. We call this the ODMAP (Overview, Data, Model, Assessment and Prediction) protocol, as its components reflect the main steps involved in building SDMs and other empirically-based biodiversity models. The ODMAP protocol serves two main purposes. First, it provides a checklist for authors, detailing key steps for model building and analyses, and thus represents a quick guide and generic workflow for modern SDMs. Second, it introduces a structured format for documenting and communicating the models, ensuring transparency and reproducibility, facilitating peer review and expert evaluation of model quality, as well as meta-analyses. We detail all elements of ODMAP, and explain how it can be used for different model objectives and applications, and how it complements efforts to store associated metadata and define modelling standards. We illustrate its utility by revisiting nine previously published case studies, and provide an interactive web-based application to facilitate its use. We plan to advance ODMAP by encouraging its further refinement and adoption by the scientific community.     

Temporal fluctuation in abundance of Brown-headed Cowbirds and their hosts in riparian habitat in the Okanagan Valley, British Columbia, Canada

ABSTRACT.   We tested the hypothesis that the abundance of Brown-headed Cowbirds ( Molothrus ater ) and their hosts, as well as parasitism rates, changed between 1992–1993 and 2001–2003 in riparian habitats in the Okanagan Valley, British Columbia, Canada, where riparian habitat has been reduced in area by more than 85% over the past 60 years. Cowbird abundance declined from a mean of 2.1 and 1.9 individuals per census plot in 1992 and 1993, respectively, to 0.66 individuals per plot in 2001–2002. The mean number of potential host individuals per census plot was also lower in 2001–2002 (5.5) than in 1992 (7.0) and 1993 (7.8). Although the percentage of Yellow Warbler ( Dendroica petechia ) nests parasitized declined (77% in 1992–1993 to 50% in 2002–2003), Yellow Warblers and Song Sparrows ( Melospiza melodia ) in the Okanagan Valley continue to be parasitized at high rates and have low nesting success. Host species and the distance of nests from the edge of nest patches were the strongest predictors of both nest success and parasitism, indicating the importance of large continuous patches of shrubs that allow nests to be located further from edges.     

Brood parasitism of White-rumped Swallows by Shiny Cowbirds

ABSTRACT.   Swallows and martins are infrequent hosts of the generalist brood parasite Shiny Cowbird ( Molothrus bonariensis ). We monitored 50 nesting attempts by White-rumped Swallows ( Tachycineta leucorrhoa ) over a two-year period in Argentina and detected low rates of brood parasitism (three nests, or 6%). Of the three nests parasitized, cowbirds ( N = 1 per nest) successfully fledged from two. Eight of 13 swallow eggs in these three nests were punctured by cowbirds, and all but one swallow nesting starved at the two parasitized nests. At least two factors may contribute to the low frequency of parasitism of White-rumped Swallows by Shiny Cowbirds, including the inability of the larger cowbirds to enter some nest cavities and the aggressive nest defense behavior of adult swallows.     

Egg rejection behavior in a population exposed to parasitism: Village Weavers on Hispaniola

In contrast to African Village Weavers (Ploceus cucullatus)that are parasitized by Diederik Cuckoos (Chrysococcyx caprius),introduced weavers on Hispaniola existed without parasitismfor at least 2 centuries until the arrival of the Shiny Cowbird(Molothrus bonariensis) in the 1970s. Cruz and Wiley (1989)found that Hispaniolan weavers had a lower rejection rate offoreign eggs than African populations. Subsequently, Robertand Sorci (1999) and Lahti (2005, 2006) found that acceptanceof dissimilar eggs is not characteristic of the species throughoutits Hispaniolan range. In 1999–2002, we studied egg rejectionin Hispaniolan weavers on a broad regional scale. Rejectionincreased as experimental eggs became increasingly differentfrom the host eggs. Rejection rates for mimetic eggs, differentcolor eggs, different-spotting eggs, and cowbird eggs was 23.2%,33.3%, 61.5%, and 85.3%, respectively, with higher rejectionof cowbird eggs in areas where cowbirds were observed. Althoughrejection is likely to have a genetic component, the differencescould be due to phenotypic plasticity. Plasticity in egg rejectionmay be expected, given the potential cost of rejection and thespatiotemporal distribution of cowbirds. Thus, egg rejectionhas not necessarily decreased in Hispaniolan weavers, but itmay act in a plastic manner, increasing where cowbirds are present.     

feedr and animalnexus.ca: A paired R package and user‐friendly Web application for transforming and visualizing animal movement data from static stations

Radio frequency identification (RFID) provides a simple and inexpensive approach for examining the movements of tagged animals, which can provide information on species behavior and ecology, such as habitat/resource use and social interactions. In addition, tracking animal movements is appealing to naturalists, citizen scientists, and the general public and thus represents a tool for public engagement in science and science education. Although a useful tool, the large amount of data collected using RFID may quickly become overwhelming. Here, we present an R package (feedr) we have developed for loading, transforming, and visualizing time‐stamped, georeferenced data, such as RFID data collected from static logger stations. Using our package, data can be transformed from raw RFID data to visits, presence (regular detections by a logger over time), movements between loggers, displacements, and activity patterns. In addition, we provide several conversion functions to allow users to format data for use in functions from other complementary R packages. Data can also be visualized through static or interactive maps or as animations over time. To increase accessibility, data can be transformed and visualized either through R directly, or through the companion site: http://animalnexus.ca , an online, user‐friendly, R‐based Shiny Web application. This system can be used by professional and citizen scientists alike to view and study animal movements. We have designed this package to be flexible and to be able to handle data collected from other stationary sources (e.g., hair traps, static very high frequency (VHF) telemetry loggers, observations of marked individuals in colonies or staging sites), and we hope this framework will become a meeting point for science, education, and community awareness of the movements of animals. We aim to inspire citizen engagement while simultaneously enabling robust scientific analysis.     

A game-theoretic model of interspecific brood parasitism with sequential decisions

The interaction between hosts and parasites in bird populations has been studied extensively. This paper uses game-theoretic methods to model this interaction. This has been done in previous papers but has not been studied taking into account the detailed sequential nature of this game. We introduce a model allowing the host and parasite to make a number of decisions which will depend on various natural factors. The sequence of events begins with the host forming a nest and laying a number of eggs, followed by the possibility that a parasite bird will arrive at the nest; if it does it can choose to destroy some of the host eggs and lay one of its own. A sequence of events follows, which is broken down into two key stages; firstly the interaction between the host and the parasite adult, and secondly that between the host and the parasite chick. The final decision involves the host choosing whether to raise or abandon the chicks that are in the nest. There are certain natural parameters and probabilities which are central to these various decisions; in particular the host is generally uncertain whether parasitism has taken place, but can assess the likelihood of parasitism based upon certain cues (e.g. how many eggs remain in its nest). We then use this methodology to model two real-world interactions, that of the Reed Warbler with the Common Cuckoo and also the Yellow Warbler with the Brown-headed Cowbird. These parasites have different methods in the way they parasitize the nests of their hosts, and the hosts can in turn have different reactions to these parasites. Our model predictions generally match the real results well, and the model also makes predictions of the effect of changes in various key parameters on the type of parasitic interactions that should occur.     

Shiny Cowbird parasitism of a low quality host: effect of host traits on a parasite's reproductive success

ABSTRACT.   The reproductive success of parasitic cowbirds ( Molothrus spp.) varies among host species and is influenced by the degree of synchronization in timing of egg laying, the duration of parasite and host incubation periods, and the ability of hosts to incubate and rear parasite young. We studied the reproductive success of Shiny Cowbirds ( Molothrus bonariensis ) that parasitized the nests of Creamy-bellied Thrushes ( Turdus amaurochalinus ) in the Monte desert region of Argentina. Shiny Cowbirds frequently parasitized Creamy-bellied Thrush nests (60%), and most cowbirds synchronized egg laying with that of thrushes (79%). Most parasitic eggs (80%) hatched within 1 d of the hatching of the first host egg, and more than 91% of the eggs survived until the end of the incubation. However, only 60% of the cowbird eggs hatched and 52% of young survived. The proportion of Shiny Cowbirds eggs laid in Creamy-bellied Thrush nests that resulted in fledged young was 0.03, including eggs and young lost due to predation or desertion. Despite this low reproductive success, Creamy-bellied Thrushes were heavily parasitized by Shiny Cowbirds in our study area. Shiny Cowbirds may continue to parasitize these thrushes because of diffuse selection or because Shiny Cowbird chicks are more likely to fledge from Creamy-bellied Thrush nests in years or areas with greater food availability when brood reduction does not occur.