A comparison of success rates of introduced passeriform birds in New Zealand, Australia and the United States

In this study, we compiled lists of successful and unsuccessful passeriform introductions to nine sites in New Zealand, Australia and the United States. We limited our analysis to introductions during the 19th century to minimize potential variation in transport modes and habitat quality changes, such as those due to increasing urbanization. We compared introduction success rates at three levels. First we included all passeriforms introduced to any of the sites in the three locations, then we compared the fates of just those species with a European origin and finally we compared success rates of just the 13 species released into all three locations. We found that the pattern of success or failure differed significantly across the three locations: Passeriforms introduced by acclimatization organizations to the United States were significantly more likely to fail than those introduced to New Zealand or Australia. Several species that succeeded in either New Zealand or Australia failed in the United States, even after the introduction of seemingly sufficient numbers

Linking complex forest fuel structure and fire behaviour at fine scales

Abstract. Improved fire management of savannas and open woodlands requires better understanding of the fundamental connection between fuel heterogeneity, variation in fire behaviour and the influence of fire variation on vegetation feedbacks. In this study, we introduce a novel approach to predicting fire behaviour at the submetre scale, including measurements of forest understorey fuels using ground-based LIDAR (light detection and ranging) coupled with infrared thermography for recording precise fire temperatures. We used ensemble classification and regression trees to examine the relationships between fuel characteristics and fire temperature dynamics. Fire behaviour was best predicted by characterising fuelbed heterogeneity and continuity across multiple plots of similar fire intensity, where impacts from plot-to-plot variation in fuel, fire and weather did not overwhelm the effects of fuels. The individual plot-level results revealed the significance of specific fuel types (e.g. bare soil, pine leaf litter) as well as the spatial configuration of fire. This was the first known study to link the importance of fuelbed continuity and the heterogeneity associated with fuel types to fire behaviour at metre to submetre scales and provides the next step in understanding the complex responses of vegetation to fire behaviour

Is propagule size the critical factor in predicting introduction outcomes in passeriform birds?

Influential analyses of the propagule pressure hypothesis have been based on multiple bird species introduced to one region (e.g. New Zealand). These analyses implicitly assume that species-level and site-level characteristics are less important than the number of individuals released. In this study we compared records of passerine introductions with propagule size information across multiple regions (New Zealand, Australia, and North America). We excluded species introduced to just one of the three regions or with significant uncertainty in the historical record, as well as species that succeeded or failed in all regions. Because it is often impossible to attribute success to any single event or combination of events, our analysis compared randomly selected propagule sizes of unsuccessful introductions with those of successful introductions. Using Monte Carlo repeated sampling we found no statistical support for the propagule pressure hypothesis, even when using assumptions biased toward showing an effect

A reassessment of the role of propagule pressure in influencing fates of passerine introductions to New Zealand

Several studies have argued that principal factor in determining the fate of bird introductions is introduction effort. In large part, these studies have emerged from analyses of historical records from a single place—New Zealand. Here we raise two concerns about these conclusions. First, we argue that although many bird species were introduced repeatedly to New Zealand, in many cases the introductions apparently occurred only after the species were already successfully naturalized. The inclusion of such seemingly superfluous introductions may exaggerate the importance of propagule pressure. And second, we question the reliability of the records themselves. In many cases these records are equivocal, as inconsistencies appear in separate studies of the same records. Our analysis indicates that species were successful not because they were introduced frequently and in high numbers, but rather it is likely that they were introduced frequently and in high numbers because the initial releases were successful

Propagule size and patterns of success in early introductions of Chukar Partridges (Alectoris chukar) to Nevada

ABSTRACT Background: In an effort to combine the well-known evolutionary phenomenon of increased extinction probability in small populations with invasion biology models, some studies have concluded that propagule size is the primary determinant of establishment success in introduced birds. Question: Is establishment success in Chukar Partridges (Alectoris chukar) introduced to the state of Nevada predicted by propagule size, by location of release, or by the source (game farm or wild-caught)? Methods: We compared propagule sizes of successful and unsuccessful introductions of Chukar Partridges in Nevada, using logistic regression. We included tests for possible differences across introduction sites (i.e. counties) and between birds that originated from game farms or were wild-caught. Findings: Propagule size was not a significant predictor of introduction success. Moreover, we found no significant differences across 17 sites, or between wild birds and those from game farms. Conclusions: It appears most likely that site-level factors such as the availability of habitat are more important to the success of introductions than is propagule size

The Earliest House Sparrow Introductions to North America

Several authors have argued that three separate introductions of roughly 100 individuals were required initially to establish the House Sparrow (Passer domesticus) in the Brooklyn, New York area. We argue that these claims are in error and that the actual record suggests that it is likely the initial introduction of just 16 birds in 1851 was all that was required to establish the species in New York. We further suggest that a similar level of scrutiny of historical records will reveal more examples of misinterpretations and errors, casting doubt on the validity of studies that claim propagule pressure has played an important role in determining the fate of bird introductions

Development of a GPS Forest Signal Absorption Coefficient Index

In this paper GPS (Global Positioning System)-based methods to measure L-band GPS Signal-to-Noise ratios (SNRs) through different forest canopy conditions are presented. Hemispherical sky-oriented photos (HSOPs) along with GPS receivers are used. Simultaneous GPS observations are collected with one receiver in the open and three inside a forest. Comparing the GPS SNRs observed in the forest to those observed in the open allows for a rapid determination of signal loss. This study includes data from 15 forests and includes two forests with inter-seasonal data. The Signal-to-Noise Ratio Atmospheric Model, Canopy Closure Predictive Model (CCPM), Signal-to-Noise Ratio Forest Index Model (SFIM), and Simplified Signal-to-Noise Ratio Forest Index Model (SSFIM) are presented, along with their corresponding adjusted R 2 and Root Mean Square Error (RMSE). As predicted by the CCPM, signals are influenced greatly by the angle of the GPS from the horizon and canopy closure. The results support the use of the CCPM for individual forests but suggest that an initial calibration is needed for a location and time of year due to different absorption characteristics. The results of the SFIM and SSFIM provide an understanding of how different forests attenuate signals and insights into the factors that influence signal absorption

Estimating GPS Signal Loss in a Natural Deciduous Forest Using Sky Photography

Understanding how Global Positioning System (GPS) signals are influenced by vegetation structure allows for the determination of how specific technologies might be affected in certain forest environments. This study presents three different models that predict signal loss in a natural deciduous forest using fisheye photography. Relationships between terrestrial-based hemispherical sky-oriented photo (HSOP) measurements and GPS signal-to-noise ratios (SNRs) are explored. ArcGIS is used for image processing of HSOPs to rapidly estimate canopy closure (CC) at particular angles from zenith in forested areas. The difference between the observed SNR of GPS L-band signals under forest canopies to those observed in the open determines signal loss. CC values at different zenith angles inside the forest during four seasons are used to model signal attenuation. This article presents a canopy closure predictive model (CCPM), a model that includes the CCPM and incorporates the difference between the CC value in any season minus the CC in the winter, and a model that includes a seasonal component. The three models presented in this article yield adjusted R2 values between 0.60 and 0.62 and root mean square error range of 3.21 to 3.28 dB

Inconsistencies among secondary sources of Chukar Partridge (Alectoris chukar) introductions to the United States

The propagule pressure hypothesis asserts that the number of individuals released is the key determinant of whether an introduction will succeed or not. It remains to be shown whether propagule pressure is more important than either species-level or site-level factors in determining the fate of an introduction. Studies claiming to show that propagule pressure is the primary determinant of introduction success must assume that the historical record as reported by secondary sources is complete and accurate. Here, examine a widely introduced game bird, the Chukar (Alectoris chukar), to the USA. We compare the records reported by two secondary sources (Long, 1981; Lever, 1987) to those in a primary source (Christensen, 1970) and to a recent study by Sol et al. (2012). Numerous inconsistencies exist in the records reported by Sol et al. (2012), Long (1981) and Lever (1987) when compared to the primary record of Christensen (1970). As reported by Christensen (1970), very large numbers of Chukars were released unsuccessfully in some states. Our results strongly imply that factors other than sheer numbers are more important. Site-to-site differences are the most likely explanation for the variation in success

Historical Records Of Passerine Introductions To New Zealand Fail To Support The Propagule Pressure Hypothesis

Blackburn et al. (Biodiver Conserv 20:2189-2199, 2011) claim that a reanalysis of passerine introductions to New Zealand supports the propagule pressure hypothesis. The conclusion of Blackburn et al. (2011) are invalid for three reasons: First, the historical record is so flawed that there is no sound basis for identifying the mechanisms behind extinction following introduction, or whether species were successful because they were introduced in large numbers or were introduced in large numbers because earlier releases succeeded. Second, the GLIMMIX analysis of Blackburn et al. (2011) is biased in favor of the propagule pressure hypothesis. Third, the population viability analysis presented by Blackburn et al. (2011) is based on unjustified and questionable assumptions. It is unlikely that the outcome of passerine bird introductions to New Zealand depended on species characteristics, site characteristics, and human decision more than on a simple summing of the numbers introduced