Population-level effects of PbThe potential effects of Pb poisoning on individual birds are clearly established. Far less clear are the population-level consequences of current rates of Pb exposure in many species. The best examples are from waterfowl, in which losses to Pb poisoning were estimated to be 2–3% overall, with an estimated 4% annual loss in Mallards (Anas platyrhynchos; Sanderson and Bellrose 1986). Similarly, Grand et al. (1998) estimated that survival rates of female Spectacled Eiders (Somateria fischeri) exposed to Pb shot from ingestion were 34% lower than those of unexposed females (77%) and suggested that Pb exposure may have been preventing local population recovery. California Condor populations appear to be at substantial risk from Pb exposure (e.g., Cade 2007, Walters et al. 2010, Finkelstein et al. 2012). Pb sinkers appear to be a regulatory factor for Common Loons in New Hampshire, where 49% of known mortalities are attributed to Pb poisoning from fishing tackle (Vogel 2013).
Significance of Pb exposure to avian conservation
Given proof that elevated Pb exposure can greatly influence the health of individual birds and can result in mortality, the environmental distribution of Pb from ammunition and fishing tackle could be an important factor influencing the conservation of avian communities. Here, we discuss (1) the apparent contradiction in results of some studies regarding avian exposure and levels of impairment caused by different contaminant concentrations; (2) unease with the implicit assumption of many published studies that Pb is the ultimate source of mortality for birds found dead with elevated Pb concentrations; and (3) lack of clarity over the relative threat of Pb to birds in comparison to other major impacts such as invasive species, habitat loss, human disturbance, domestic cats, and collisions with vehicles, power transmission lines, and buildings.
We have already presented several examples of increases in avian Pb exposure in association with ammunition and tackle. Similarly, we have outlined many instances of toxicity associated with environmental and lab-derived exposure to Pb. However, the results of other studies add a layer of ambiguity to this topic that is important to acknowledge. For example, even at relatively similar Pb exposure levels, studies have shown clear effects on blood chemistry (Kerr et al. 2010, Carpenter et al. 2003, Hoffman et al. 1981, Pattee et al. 2006), egg production (Edens and Garlich 1983), behavior (Burger and Gochfeld 1994, 2004), and survival (Schulz et al. 2006, Grand et al. 1998, Pattee et al. 2006, Rideout et al. 2012), whereas others demonstrated limited responses to many of the same endpoints (McBride et al. 2004, Schulz et al. 2007, Ferrandis et al. 2008). Although differences in methodology likely played some role, a more plausible explanation is intrinsic interindividual and interspecific variability in sensitivity to Pb. This source of variation complicates overall estimates of Pb risk to avian communities and represents a key data gap in Pb ecotoxicology.
Acute toxicity leading to mortality can often be determined from physical or behavioral cues, especially if tissues are analyzed for Pb content postmortem. But it is uncommon to encounter Pb-intoxicated birds for which this information can be obtained, which complicates attempts to estimate actual mortality due to Pb. As a result, numerous studies have reported Pb levels in tissues from dead birds, making the implicit assumption that mortality was a result of Pb exposure in those birds with elevated concentrations (Helander et al. 2009, Hernández and Margalida 2009, Kenntner et al. 2001, Wayland and Bollinger 1999). In some cases, mortality is likely due to Pb poisoning, but as we noted above, the tremendous range in sensitivities among individuals and species can make the use of tissue thresholds to infer cause of death problematic. Thus, the proportion of birds found dead with elevated Pb concentrations is often a poor and biased (under or over) estimator of mortality rates.
The cumulative body of scientific evidence unequivocally suggests that Pb exposure from ammunition and fishing tackle is directly responsible for numerous bird deaths each year and is clearly a serious threat to the population trajectory of the endangered California Condor (Franson et al. 2003, Walters et al. 2010, Finkelstein et al. 2012; Box 2). However, for many bird species, the impact of Pb exposure is much less clear given the assortment of other anthropogenic hazards and conservation threats they face. For example, >1 billion birds year−1 are estimated to be killed by domestic cats in the United States (Loss et al. 2013), and millions of bird mortalities each year result from collisions with power lines, fixed objects, and vehicles (Loss et al. 2014). In addition, habitat loss and intensified land use can have an immeasurable impact on the conservation status of many bird species at global scales. However, addressing the Pb issue is tractable because it entails a relatively simple solution: replacing Pb-based ammunition and fishing tackle with non-Pb alternatives.
Proponents of this solution contend that alternatives to Pb are readily available and of comparable cost and that the costs are expected to decrease with increases in demand that accompany improved efficiencies in ballistics (Thomas 2013). Conversely, supporters of continued Pb use in ammunition and fishing tackle argue that the increased costs of non-Pb alternatives require robust and clear scientific evidence of impacts before any changes are made. However, these competing ideas are not mutually exclusive. Progress could be made in reasonably short order to reduce avian Pb exposure and increase scientific knowledge of Pb's impacts through an integrated plan of voluntary Pb replacement programs coupled with large-scale research efforts to evaluate the effects of Pb management on avian Pb exposure.
Tedy: máme dobré důkazy o vlivu na populace vodních ptáků (a jednoho kondora) a podezření i jinde, ale vliv na populace těžko odhadnout z toho, že se prostě občas najde otrávený pták. Zakazujme to tedy olověné broky na vodní ptáky, propagujme alternativy jinde a sbírejme důkazy.
Poprvé teď vidím celkem úctyhodný výčet od Fishera et al., důkaz o vlivu na ptačí populace to není, ale je to tedy opravdu hodně případů otrav.
Ještě jsem si zase otevřel pár těch studií, ale tam už nic moc dalšího zajímavého nebylo, možná kromě doplnění dalšího mrchožrouta do seznamu těch, kde je to podstatná mortalita - orla mořského z Isomursu et al., 2018