Invasive American Mink Research Articles

Population genetic structure of the invasive American mink (Mustela vison) in France: evidence of a high genetic diversity and the existence of multiple genetic lineages

Population genetic structure of the invasive American mink (Mustela vison) in France: evidence of a high genetic diversity and the existence of multiple genetic lineages

Confirmation of the invasive American mink (Neogale vison) as carrier of Mycobacterium bovis in southern Chile

Bovine tuberculosis (bTB) is a chronic infectious-contagious disease with worldwide distribution, caused by the zoonotic pathogen Mycobacterium bovis. It is believed that the existence of wild cycles may hamper the success of bTB control strategies worldwide, where wildlife species could be reservoirs of this bacterial agent across their native (e.g., European badgers, wild boars) or non-indigenous (e.g., brushtail possum in New Zealand) ranges. However, further studies are required to understand the potential risk posed by non-native wildlife in becoming carriers of M. bovis in other neglected latitudes, such as the Southern Cone of South America. In this study, we performed a specific M. bovis-RD4 real-time PCR (qPCR) assay to detect bacterial DNA in tissues from the invasive American mink (Neogale vison) in Los Ríos region, Chile. We detected M. bovis DNA in blood samples collected from 13 out of 186 (7 %) minks with known sex and age. We did not find any significant differences in bacterial DNA detection according to mink sex and age. We found that 92 % (12/13) of specimens were positive in lung, 39 % (5/13) in mediastinal lymph node, and 15 % (2/13) in mesenteric lymph node, which suggest that both respiratory and digestive pathways as possible routes of transmission between infected hosts and minks. Our study is the first report on M. bovis molecular detection in invasive minks in an area where the largest cattle population in the country is located. Furthermore, this area is characterized by a low within-herd prevalence of M. bovis infection in cattle, with a relatively low number of infected herds, and so far, no attempts at eradicating the disease have been successful.

Dynamic connectivity analyses to inform management of the invasive American mink and its native competitor, the European mink

Forecasting habitat suitability and connectivity can be central to both controlling range expansion of invasive species and promoting native species conservation, especially under changing climate conditions. This study aimed to identify and prioritize areas in Spain to control the expansion of one of the most harmful invasive species in Europe, the American mink, while conserving its counterpart, the endangered European mink, under current and future conditions. We used ensemble habitat suitability and dynamic connectivity models to predict species ranges and movement routes considering likely climate change under three emission scenarios. Then, using habitat availability metrics, we prioritized areas for invasive mink control and native mink conservation and classified them into different management zones that reflected the overlap between species and threat from American to European minks. Results suggest that both species are likely to experience declines in habitat and connectivity under climate change scenarios with significantly larger declines by the end of the century for European minks (72 and 80% respectively) than for American minks (41 and 32%). Priority areas for management of both species varied over time and across emission scenarios, with a general shift in priority habitat towards the North-East of the study area. Our findings demonstrate how habitat suitability and dynamic connectivity approaches can guide long-term management strategies to control invasive species and conserve native species while accounting for likely landscape changes. The simultaneous study of both invasive and native species can support prioritized management action and inform management planning of the intensity, extent, and techniques of intervention depending on the overlap between species.

Conservation measures for the Caspian Tern Hydroprogne caspia at the largest colony in Sweden

We present conservation actions during 2007–2020 as part of the national Caspian Tern Hydroprogne caspia species action plan at Stenarna in the Björn archipelago, Uppland, the largest colony in Sweden. We applied a combination of monitoring, research, and management measures conducted within an adaptive approach framework, using both established and novel techniques. The implementation of conservation measures led to increased breeding success, from 0 fledglings per pair in 2007 to 1.3 in 2020. A surveillance video camera installed in 2009 aided in monitoring efforts and also revealed predation by Herring Gull Larus argentatus and White-tailed Eagle Haliaeetus albicilla, leading to species-specific control strategies. Management of the island and surrounding archipelago, including hunting of invasive American mink Mustela vison, vegetation removal, and habitat restoration after a severe storm, have also been instrumental to the success of the project. Implementation of projects such as this have the potential to improve conditions for continued viability of endangered species in a changing world and are likely to be useful to other conservation practitioners.

Polecat body size and sex ratio change over time: Impact of invasive competitor or climate warming?

Change in body size is considered to be one of the animal responses to climate warming, although in many cases it is difficult to show whether it is evolutionary or a result of phenotypic plasticity. In this study, we analysed long-term changes in the body size and sex ratio of the European polecat Mustela putorius in relation to two factors: climate warming and competition with the invasive American mink Neovison vison . In the years 1959–2021, the average body mass of polecats inhabiting north-eastern Poland increased from 869 to 1109 g in males and from 449 to 690 g in females, whereas structural body size (the condylobasal length of the skull) increased from 64.4 to 68.0 mm in males and from 55.9 to 59.6 mm in females. The rates of these increases were different for both measures; in consequence, the index of body condition changed non-linearly over time with a high increase in last 30–40 years. The observed increase in polecat body mass and skull size correlated with the rise of mean winter and summer temperatures. We explain the recorded trends by easier access to amphibians (the staple food of polecats in the study area) in mild winters, which increases the survival rate of larger polecats and/or leads to a faster growth rate of subadults in warmer summers. Competition for food between the native polecat and invasive mink could play a role in the increase of polecat body size simultaneously with climate warming, but the timing of recorded changes suggests the second factor to be more important. Our study also confirmed a previous observation of increasing skewed sex-ratio towards polecat males, which, similarly to changes in polecat body size, could have resulted both from climate warming and competition with mink.

Emergent trophic interactions following the Chinook salmon invasion of Patagonia

AbstractIn their native range, Pacific salmon (Oncorhynchus spp.) have strong interactions with a multitude of species due to the annual pulse of marine‐derived nutrients that they deliver to streams and forests when they spawn and die. Over the past few decades, Chinook salmon (Oncorhynchus tshawytscha) has established non‐native populations throughout the Patagonia region of southern South America. Here, we provide the first assessment of the pathways through which salmon‐derived nutrients enter stream and forest food webs in Patagonia by surveying multiple streams in southern Chile to identify invertebrate and vertebrate consumers of salmon carcasses and summarizing all documented trophic interactions of Chinook salmon in Patagonia. Blowflies (Calliphoridae) were the dominant colonizer of carcasses in the riparian zone, and midge flies (Chironomidae) were the most common invertebrate on submerged carcasses. Camera trap monitoring in the riparian zone revealed consumption of carcasses or carcass‐associated invertebrates by the insectivorous passerine bird “chucao” (Scelorchilis rubecula), small rodents (black rat Rattus rattus, house mouse Mus musculus, and/or colilargo Oligoryzomys longicaudatus), the South American fox “culpeo” (Lycalopex culpaeus), and the invasive American mink (Neovison vison). A mink was filmed transferring a carcass from stream to streambank, indicating that vertebrate scavenging likely increases the degree to which marine‐derived nutrients enter terrestrial food webs. The native taxa that consume salmon are closely related to species that benefit from salmon consumption in North America, suggesting that the pathways of salmon nutrient incorporation in North American food webs have functionally re‐emerged in South America. Similarly, non‐native trout (Oncorhynchus mykiss and Salmo trutta) and mink consume salmon in Patagonia, and their eco‐evolutionary history of coexistence with salmon could mean that they are preadapted for salmon consumption and could thus be key beneficiaries of this invasion. Expanded monitoring of the abundance and impacts of salmon will be vital for understanding how these novel inputs of marine‐derived nutrients alter Patagonian food webs.

Does the American mink displace the European polecat? A need for more research on interspecific competition between invasive and native species

Introduced alien species can negatively affect native competitors by reducing their populations or eliminating them from ecosystems. However, studies do not always find evidence for anticipated impacts, and changes in native populations can be difficult to estimate. Interactions between the invasive American mink Neovison vison and native European polecat Mustela putorius have been studied in several countries, but the mink’s impact on polecat populations at a large spatiotemporal scale remains unclear. In the years 1995–2018, we live-trapped mink and polecats at 60 study sites in Poland, and we analysed hunting bags of mink and polecats from the years 2009–2018. During 13,766 trap-nights, we captured 905 individuals. Mink comprised 91.2% and polecats 8.8% of trapped animals. The mean mink and polecat trappability was 6 and 0.6 individuals per 100 trap-nights, respectively. At rivers, polecat and mink trappability were negatively correlated, whereas at lakes, they were not correlated. The sex ratio of trapped polecats was more skewed toward males than that of mink. Mink comprised 63.6% and polecats 36.4% of 59,831 animals killed by hunters. Over 10 years, the numbers of mink shot annually increased slightly, whereas the numbers of polecat decreased slightly. There was a positive correlation between numbers of mink and polecats shot annually. We found weak evidence that at a large spatiotemporal scale, the invasion of mink has led to a decline in polecat numbers. Although the datasets we analysed were based on large samples, they were insufficient to show evidence of competitive interactions between these two mustelids.

Invasive American mink (Neovison vison) as potential definitive host of Sarcocystis elongata, S. entzerothi, S. japonica, S. truncata and S. silva using different cervid species as intermediate hosts.

Canids and scavenger birds were shown to act as definitive hosts of numerous Sarcocystis species using members of the Cervidae family as an intermediate host, whereas definitive hosts spreading closely related S. elongata, S. entzerothi, S. japonica, S. matsuoae, S. rangiferi, S. truncata, S. silva and S. tarandi remain unknown. In the current study, the intestine samples of 40 American minks (Neovison vison) were molecularly tested for the presence of the above-mentioned Sarcocystis spp. Species-specific PCR of cytochrome c oxidase subunit I (cox1) fragments and subsequent sequencing revealed the presence of sporocysts/oocysts of five species, S. elongata (n=2), S. entzerothi (n=10), S. japonica (n=4), S. silva (n=13) and S. truncata (n=21) in the analysed samples. Sarcocystis infection was confirmed in 32/40 (80%) examined samples. In addition, half of the infected animals (50%) were infected with multiple Sarcocystis species suggesting that American minks had access to meat of different deer species, such as roe deer, red deer and sika deer. This causes concern about compliance of hunters and game processing companies with game waste management rules. Further research on the involvement of mustelids in the transmission of various Sarcocystis spp. from different geographical locations is needed.

Low individual diet variation and high trophic niche overlap between the native polecat and invasive American mink

AbstractIntroductions of invasive species increase competitive interactions in a community proportionally to the similarity between the ecological niches of invasive and native species. Food represents one of the most important resources influencing competition, and differences in the trophic niche of native and invasive species can affect their ability to coexist. Moreover, in sympatric native and invasive species of similar body size and high sexual dimorphism, competition for food between individuals of the same sex may be higher than intraspecific competition between males and females, thus making the overall competitive interactions more complex. The aim of this study was to investigate the intraspecific and intrasexual competition for food resources between two sexually dimorphic mustelids, the native polecat Mustela putorius and invasive American mink Neovison vison, in riparian habitats of Białowieża Forest (Poland). Based on an analysis of 1215 scats, we studied the food habits of eight polecat and 24 mink individuals. The trophic niches of the polecat and mink were narrow and overlapped considerably. The diet of both predators was dominated by amphibians (mainly the common frog Rana temporaria), which comprised up to 94.1% and 89.7% of polecat and mink prey biomass, respectively. Individual diet variation was low within each sex group of both species. Interspecific similarities in body mass of the sexes and intraspecific differences in body mass between the sexes did not affect pairwise niche overlaps. However, we observed some mechanisms of food segregation between the sexes and species that reduced intra‐ and interspecies competition. Polecat males hunted more common toads Bufo bufo than polecat females, mink males and mink females. They also hunted larger frogs than polecat females, and the opposite pattern was recorded in mink. We conclude that two predator species exploiting abundant prey can coexist despite a very high overlap in their food niches.

A cost-effective PCR–RFLP method for monitoring invasive American mink: preliminary field test in control areas of Spain

American mink Neovison vison is a semi-aquatic mustelid that has been introduced throughout Europe. Several attempts to eradicate this invasive species have been carried out since its spread. In the Iberian Peninsula, an eradication program has started since 2001, as part of the national action plan for the conservation of European mink Mustela lutreola. Proper detection is crucial for management, both for monitoring variation in mink abundance and prevent the recolonization of cleared areas. Mink scats can be confounded with those of several same-sized mustelids, and with the spraints of Eurasian otter Lutra lutra, which also occur along watercourses. However, these difficulties can be overcome by non-invasive genetic methods. With the aim of providing a cost-effective and reliable technique for differentiating mink scats from those of the largest possible number of species with morphologically similar scats, we tested the effectiveness of an already available faecal mtDNA-based PCR–RFLP method for distinguishing mink- and otter faeces. We then applied the method for analysing scats collected and identified in the field by trained surveyors for monitoring the success of mink control operations. The PCR–RFLP method clearly differentiated mink scats from those of otters, as restriction enzymes produced well-defined different patterns. Eighty-five percent of 94 faecal samples could be assigned to a mustelid species. Only three out of seven putative mink samples were confirmed, suggesting that the accuracy of the visual identification of scats is questionable and genetic methods are needed for the reliable assessment of the success of eradication programs.

Digestive tract nematode infections in non-native invasive American mink with the first molecular identification of Molineus patens.

Parasites may negatively affect hosts condition, especially when infection intensity is high. Species introduced to a new habitat are often less exposed to a parasite pressure but may accumulate parasites in time. American mink (Neovison vison) introduced to Europe, Asia, and South America is an example of such invasive species. We analysed nematode prevalence and digestive tract infection intensity in 796 feral American mink from Poland. The analyses were performed separately for stomach, duodenum, small intestine and large intestine. Parasite species identification was performed using molecular methods based on highly conserved nuclear 18S rRNA gene and supplemented with morphological analysis. In total, we collected 26,852 nematodes and 98.6% of them were isolated from mink stomachs. We found positive association between infection intensity in stomach and other parts of digestive tract. Nematode prevalence was estimated at 63.8% and average infection intensity per one American mink at 52.9 (range from 1 to 1118). If the stomach results were theoretically and intentionally omitted the prevalence was 5 times lower (12.7%) and infection intensity 14 times lower (3.7; range 1–50). We identified two nematode species in digestive tracts of American mink: Aonchotheca putorii and Molineus patens. The 18S rRNA gene sequence of Molineus patens has been reported for the first time. The results showed that Aonchotheca putorii is a dominating nematode in the invasive American mink and that it inhabits stomach intensively and preferably.

Using DNA metabarcoding to investigate diet and niche partitioning in the native European otter (Lutra lutra) and invasive American mink (Neovison vison)

In the UK, the native European otter (Lutra lutra) and invasive American mink (Neovison vison) have experienced concurrent declines and expansions. Currently, the otter is recovering from persecution and waterway pollution, whereas the mink is in decline due to population control and probable interspecific interaction with the otter. We explored the potential of DNA metabarcoding for investigating diet and niche partitioning between these mustelids. Otter spraints (n = 171) and mink scats (n = 19) collected from three sites (Malham Tarn, River Hull and River Glaven) in northern and eastern England were screened for vertebrates using high-throughput sequencing. Otter diet mainly comprised aquatic fishes (81.0%) and amphibians (12.7%), whereas mink diet predominantly consisted of terrestrial birds (55.9%) and mammals (39.6%). The mink used a lower proportion (20%) of available prey (n = 40 taxa) than the otter and low niche overlap (0.267) was observed between these mustelids. Prey taxon richness of mink scats was lower than otter spraints and beta diversity of prey communities was driven by taxon turnover (i.e. the otter and mink consumed different prey taxa). Considering otter diet only, prey taxon richness was higher in spraints from the River Hull catchment and beta diversity of prey communities was driven by taxon turnover (i.e. the otter consumed different prey taxa at each site). Studies using morphological faecal analysis may misidentify the predator as well as prey items. Faecal DNA metabarcoding can resolve these issues and provide more accurate and detailed dietary information. When scaled up across multiple habitat types, DNA metabarcoding should greatly improve future understanding of resource use and niche overlap between the otter and mink.

Molecular Survey of Parvoviruses and Mycoplasma spp. in Invasive American Mink (Neovison vison) from Southern Chile.

Using PCR, we evaluated the presence of parvoviruses and Mycoplasma spp. in 123 American mink (Neovison vison), an introduced invasive carnivore in Chile. Our results showed all analyzed animals were negative for both pathogen groups. We cannot completely dismiss their presence, but if present, their prevalence should be lower than 2%.

High Trophic Niche Overlap between a Native and Invasive Mink Does Not Drive Trophic Displacement of the Native Mink during an Invasion Process.

Simple SummaryInvasive species are widely recognized to negatively affect native species through both direct and indirect interactions. When diet overlap between the native and invasive species increases, their competitive interaction is expected to increase too. This in turn may lead to displacement of one of the species. However, the specific mechanisms of the diet displacement are still unclear. In this study, we analysed the diet and diet overlap between the critically endangered European mink and the invasive American mink during the invasion process of the latter species by means of stable isotope analyses. We found a significant diet overlap between the native and invasive mink when they co-occur, an important individual variation of diet, and no significant change of diet of the native species in response to the arrival of the invasive mink. These results suggest significant competitive pressure imposed on the native European mink by the invasive American mink. As such, urgent implementation of control measures of invasive species is needed to ensure the viability and conservation of endangered European mink populations.The pressure elicited by invasive species on native species significantly increases with the increase of the overlap of their ecological niches. Still, the specific mechanisms of the trophic displacement of native species during the invasion process are unclear. The effects of the invasive American mink (Neovison vison) on the critically endangered European mink (Mustela lutreola) was assessed by analyses of diet and niche overlap during the invasion process. To do this, the isotopic composition (δ13C and δ15N) of both species of mink and their four main types of prey was analysed. Significant trophic overlap between the native European mink and invasive American mink was found when they coexisted in sympatry. Furthermore, both mink species were characterised by significant individual variation in diet and no obvious change in diet of the native species in response to the arrival of the introduced species was observed. High niche overlap registered between both species in sympatry with no displacement in diet of the native mink in response to the arrival of the invasive mink is expected to have important consequences for the viability and conservation of the native mink populations, as it suggests high competitive pressure.

Detection probabilities of the native Eurasian otter and the invasive American mink are independent of their co-occurrence

Detection probability is an important input when studying and managing species. It reduces the miscalculations of the estimates of occupancy, population abundances and their trends inherent to the imperfect detection during sampling. However, detection probability may vary in relation to environmental and biological factors, such as the presence of other species of similar ecological niche. We used a two-species single-season occupancy model to analyse the detection probability of the native Eurasian otter Lutra lutra and the invasive American mink Neovison vison in the northeast of the Iberian Peninsula and to test for potential differences in their detection when co-occurring and when not. Despite the known behavioural change of American mink towards a more terrestrial diet and a more diurnal activity pattern in the presence of Eurasian otter, their detectability did not vary when both species co-occurred versus when they did not. However, we observed seasonal differences in the probability of detection. Specifically, the probability of detection was higher in winter for both species. Furthermore, Eurasian otter was more often detected in sites with clay substrate, whereas American mink in sites with clay and rocks. These results indicate that the effectiveness of monitoring of Eurasian otter and American mink remains independent of the species co-occurrence. Yet, seasonal variations in the detection should be taken into account when monitoring.

Seroprevalence of Echinococcus spp. and Toxocara spp. in Invasive Non-native American Mink

Invasive non-native species can become reservoirs of zoonotic pathogens and cause their spread during colonization, increasing the risk of zoonoses transmission to both wild hosts and humans. American mink (Neovison vison) are considered an important invasive mammal species responsible for carrying endoparasites. The aim of our study was to evaluate the role of feral American mink as a possible transmission vector of Echinococcus spp. and Toxocara spp. in wildlife. We analysed the frequency of American mink exposure to both parasites, the spatial distribution in Poland, and the variability over time on the basis of specific antibody presence using ELISA and Western blot. Alimentary tract analyses revealed that American mink do not serve as definitive hosts for these parasites. Altogether, 1100 American mink were examined. The average seropositivity for American mink was 14.2% for echinococcosis and 21.7% for toxocarosis; dual-seropositivity was detected in only 6.0%. Seroprevalence of both parasites differed between study sites and significantly increased over time in Toxocara spp. Thus, our study revealed that free-living American mink are exposed to parasites and likely to be involved in the maintenance of both Echinococcus spp. and Toxocara spp. in the wild as paratenic hosts.

The expansion wave of an invasive predator leaves declining waterbird populations behind

AbstractAimTheory predicts that the evolutionary adaptations of prey to reduce predator pressure often fail in confrontation with non‐native predators; thus, their predation usually leads to sharp declines of prey populations. However, over time, prey can develop anti‐predator adaptations, reduce predator impact and recover its population. We analyse the numerical response of multiple prey species to the impact of a non‐native predator on a large spatiotemporal scale.LocationPoland.MethodsLong‐term population dynamics of 13 waterbird species breeding in 123 sites were analysed with reference to the present and historical distribution of mink over 40 years. We rescaled the temporal waterbird dynamics to the time elapsed since the mink colonized each site.ResultsThe steepest waterbird declines were recorded up to 15 years after establishment of the mink population, and in that period, waterbird abundance averaged across the 13 studied species declined by 50% but certain species showed different patterns: the abundance of eight species declined linearly or nonlinearly, whereas the breeding populations of five other species did not change significantly. Over time, the abundance of some declining species increased slightly and tended to stabilize at a lower level. The temporal pattern of waterbird dynamics averaged across species correlated closely with temporal changes of mink density with a 4‐year time‐lag. A projection of the observed patterns shows that waterbird decline following the expansion of mink has the shape of a wave travelling from the north to the south of Poland.Main conclusionsWe conclude that the impact of the invasive American mink should be considered an important factor affecting waterbird populations at a large geographical scale. The waterbird vulnerability to mink predation is species‐specific, and over time the negative impact grows weak as mink population densities decline.

Diet of a semiaquatic invasive mammal in northern Italy: Could it be an alarming threat to the endemic water vole?

The American mink Neovison vison has been introduced to Italy for fur farms in the 1950s. Since the 1970s, free-ranging individuals are present in north-eastern Italy, where an expanding population still occurs. In our work, we aimed at assessing the seasonal diet of invasive American mink introduced to north-eastern Italy. Thus, a total of 195 mink scats (N = 73, June 2007; N = 57, September 2007; N = 65, February 2008) were collected. Scats were washed and food remains isolated and classified through comparison with reference collections and atlases. Absolute and relative frequencies, as well as the estimated volume of each prey category were computed. The endemic Italian water vole Arvicola italicus represented the staple of the diet of the American mink in June (relative frequency: 20.4%, total volume in diet: 38.1%) and September (relative frequency: 22.7%, total volume in diet: 52.0%). Other small mammals, amphibians (Rana spp. and Pelophylax spp.) and the invasive red swamp crayfish Procambarus clarkii were mostly consumed in cold months, when water voles are not available. Differently from other study areas, wading birds and fish were rarely consumed, possibly because of their low local availability, if compared with small mammals. No law currently protects the endemic water vole, which may be furtherly threatened by the potential range expansion of invasive minks. Therefore, eradication of this alien carnivore should be recommended before local population decline of water vole become irreversible, and before minks reach populations of native riverine mustelids, i.e. the western polecat and the Eurasian otter.

Space use, habitat selection and daily activity of water voles Arvicola amphibius co-occurring with the invasive American mink Neovison vison

A water vole Arvicola amphibius population inhabiting midfield ponds was studied by live-trapping, radio-telemetry and with camera traps. Within the midfield ponds, water voles did not prefer any particular type of littoral vegetation and avoided open water areas within the ponds. The mean distance of daily movements was 118 m for males and 53 m for females. The maximum distance between two locations of a radio-tracked individual within its home range during the whole study period was 450 m. Water vole movements between the studied ponds were very limited. Most of the hiding places were located in the areas around ponds. Water voles were active mostly during the night.

Spatio-temporal variation in nesting success of colonial waterbirds under the impact of a non-native invasive predator

Colonial breeding in birds provides protection from predators and may be particularly important when birds have to cope with an invasive predator. The probability of nest predation in a colony can vary depending on several factors, such as the nest’s location in the colony and the level of aggregation of nests. We studied the nesting success of colonial great crested grebes and monitored the occurrence of the non-native invasive American mink in the colony. From among 92 grebe nests, 54.3% were successful. The daily survival rate (DSR) of grebe nests was positively affected by the increasing distance between the nest and lake shoreline, and negatively affected by the increasing distance between the nest and the five nearest grebe nests. The probability of mink occurrence in the colony increased with consecutive days of the breeding season and decreased with increasing distance from the lake shoreline. The DSR of grebe nests decreased with the increasing probability of mink occurrence along the shoreline distance gradient and the day of the breeding season. The results of the study confirm the impact of the American mink on waterbirds during the breeding season but also indicate that large breeding colonies are partially safe from mink predation, and that nest accessibility and the dilution effect influence the probability of nest survival. Our data suggest that the limited access to safe breeding sites on large lakes that can supply adult grebes and their chicks with food may affect bird productivity and population numbers at the landscape level.