Raven Numbers Research Articles

Identification of Novel Can Manipulation Behaviour in the Common Raven (Corvus corax)

This study examines the common raven (Corvus corax) population on Lanzarote, Spain, at a previously unstudied site. The study aimed to compare the use of camera trap technology and human observation in capturing a wide repertoire of raven behaviour and pay close attention to the perforation of aluminium cans, a behaviour that has not been described in the scientific literature previously but has been reported anecdotally through human observation. Five cameras were sited over a period of 6 months, with three aluminium cans placed at each location. One of the three cans was baited with meat and eggs, mimicking wild feeding substrate. Human observations took place over the same period of time in the same locations. Raven sightings were highly correlated in human-inhabited areas as well as agricultural areas, seemingly linked to food acquisition. Camera trap technology identified a greater number of can-orientated behaviours (interaction, manipulation, peeking inside, and pecking) compared to the human observation method. Conversely, human observation yielded a greater number of non-can-orientated behaviours (analysed as a group) when compared to that of camera trap observation. Overall, there was a significantly greater number of ravens observed via human observation when compared to that of camera trap observation. Initial evidence suggests that ravens only perforate cans they deem salient in terms of food acquisition, with beer cans being the most common focus of the behaviours observed, possibly linked to olfactory stimuli, the movement of the can or learned behaviour relating to reward acquisition. This study presents new data regarding object interaction in ravens, adding to the current body of knowledge.

A spatially explicit modeling framework to guide management of subsidized avian predator densities

AbstractAnthropogenic resource subsidization across western ecosystems has contributed to widespread increases in generalist avian predators, including common ravens (Corvus corax; hereafter, raven). Ravens are adept nest predators and can negatively impact species of conservation concern. Predation effects from ravens are especially concerning for greater sage‐grouse (Centrocercus urophasianus; hereafter, sage‐grouse), which have experienced prolonged population decline. Our objectives were to quantify spatiotemporal patterns in raven density, evaluate sage‐grouse nest success concurrent with fluctuating raven densities, and demonstrate a spatially explicit decision support tool to guide management applications to appropriate conflict areas. We combined ~28,000 raven point count surveys with data from more than 900 sage‐grouse nests between 2009 and 2019 within the Great Basin, USA. We modeled variation in raven density using a Bayesian hierarchical distance sampling approach with environmental covariates on detection and abundance. Concurrently, we modeled sage‐grouse nest survival using a hierarchical frailty model as a function of raven density and other environmental covariates that influence the risk of nest failure. Raven density commonly exceeded 0.5 ravens km−2and increased at low elevations with more anthropogenic development and/or agriculture. Reduced sage‐grouse nest survival was strongly associated with elevated raven density (e.g., >0.5 ravens km−2) and varied with topographic ruggedness, shrub cover, and burned areas. For conservation application, we developed a spatially explicit planning tool that predicts nest survival under current and reduced raven numbers within the Great Basin to help direct management actions to localized areas where sage‐grouse nests are at highest risk of failure. Our modeling framework can be generalized to multiple species where spatially registered abundance and demographic data are available.

Winter Ecology and Spring Dispersal of Common Ravens in Wyoming

Numbers of Common Ravens (Corvus corax) have increased in western North America, and these high abundances are the source of problems throughout the species' range. Little is known about the winter ecology of ravens. We studied a population of ravens in Wyoming during the winters of 2013–2015; our goals were to examine use of landfills for foraging and use of anthropogenic structures for roosting, as well as dispersal patterns of ravens from these landfills in the spring. On average, 22% of radio-marked ravens foraged at landfills on a given day and 68% roosted at anthropogenic sites (e.g. on buildings or underneath bridges) each night. Daily counts at an anthropogenic roost and at the nearest landfill were positively correlated. Decreased temperatures increased raven use of landfills and anthropogenic roost sites. In the spring, radio-marked and GPS-marked ravens (n = 56) dispersed an average of 38 km from the landfills where they were captured. Use of landfills and anthropogenic roost sites in the winter likely contributes to an increase in the number of ravens by improving survival and body condition of breeding-age birds. In the spring, ravens moved outward from these locations, and the area most susceptible to raven damage was localized within a 40-km radius of where ravens wintered.

Adult sage‐grouse numbers rise following raven removal or an increase in precipitation

ABSTRACTWeather and lethal control of common ravens (Corvus corax; hereafter, ravens) can affect the nesting success of greater sage‐grouse (Centrocercus urophasianus), but implications of these effects in terms of the subsequent size of the breeding population are unknown. We used generalized linear mixed models to assess the effects of weather and raven removal on sage‐grouse lek trends within Wyoming, USA, from 2008 to 2015 by counting male sage‐grouse at leks within 8 circular sites each with a 16‐km diameter and 4 circular sites with a 24‐km diameter. We compared sites where U.S. Department of Agriculture/Animal and Plant Health Inspection Service Wildlife Services (WS) removed ravens the previous year (removal sites) with other areas where they did not (nonremoval sites). Wildlife Services intensified removal efforts beginning in 2012; and, 1‐year later, WS started removing ravens to benefit sage‐grouse (i.e., raven removal was conducted near prime nesting habitat for sage‐grouse). Raven densities decreased 50% from 2008 to 2014 in removal sites, but increased in nonremoval sites by 42% based on 6,255 point counts conducted at 1,154 random locations. We hypothesized that adult sage‐grouse numbers would be greater at the 30 leks in removal sites compared with the 28 leks in nonremoval sites. The top AICc model showed that the percent change in raven numbers, minimum temperatures during the brood‐period, and precipitation during the brood‐period were informative predictors of lek counts during the next year. Fewer ravens, cooler temperatures, and more precipitation were associated with more adult males on leks. Cooler temperatures and more precipitation probably increased the survival of sage‐grouse chicks indirectly by increasing their forage, while a decrease in raven numbers may have increased nest success rates. This study was one of the first to demonstrate a positive correlation between these variables and changes in the number of adult male sage‐grouse on leks in the subsequent year. © 2017 The Wildlife Society.

Predators, predator removal, and sage‐grouse: A review

ABSTRACTPopulations of greater sage‐grouse (Centrocercus urophasianus; sage‐grouse) have been in a decline since the nineteenth century. We used our research, unpublished reports, and scientific literature to identify which predators kill sage‐grouse and to assess whether lethal control of these predators benefited the species. We also asked state wildlife biologists and scientists whether they had ever witnessed a predator kill sage‐grouse. We identified 266 instances where the predator responsible for depredating nests or killing juvenile or adult sage‐grouse could be ascertained. Most adult sage‐grouse were killed by eagles (Accipitridae), owls (Strigiformes), coyotes (Canis latrans), or red foxes (Vuples vulpes). Based on nest cameras, most depredated eggs are taken by common ravens (Corvus corax), badgers (Taxidae taxus), or coyotes. There are too few studies to conclude that predator removal increases survival rates of juvenile or adult sage‐grouse. No study has been conducted to determine whether badger removal increases nest success of sage‐grouse, and the only study on coyote removal produced ambiguous results. Several studies reported that more sage‐grouse nests are successful (i.e., >1 eggs hatched) in areas where common ravens were removed or in areas where raven densities were lower than in other areas. The data we reviewed did not indicate predators played a role in the decline during the past century, but increasing numbers of ravens since the 1970s may have contributed to the declining sage‐grouse populations in recent decades. We conclude that removing common ravens can increase nest success, although not necessarily sage‐grouse abundance. Without a better understanding of sage‐grouse and their predators, wildlife biologists will be handicapped in their efforts to prevent sage‐grouse populations from continuing to decline. © 2016 The Wildlife Society.

Catching Large Groups of Ravens: A Note on Procedures using Rocket Nets

ABSTRACT Capturing Common Ravens (Corvus corax) is very difficult. Several methods are currently used, but none effectively catch large numbers (>25 birds) of ravens at one time. Efficient capture of large numbers of ravens is needed for some autecology studies. We describe and evaluate the effectiveness of using a prebaited rocket net trapping method for simultaneously capturing large numbers of ravens. The study sites were within 2 landfills in California's Mojave Desert, one at Edwards Air Force Base and the other at Fort Irwin National Training Center. We captured 283 ravens on 5 trapping occasions between 1995 and 1997, with an average of 57 birds per trapping occasion. We observed greater numbers of ravens at the bait sites with increasing bait duration, and these numbers appeared to level off after 25 to 30 days of baiting. Longer bait durations may habituate ravens to the resource and compensate for their wariness, which could increase capture success. More than half of the ravens captured (55%) w...

Effi cacy of CPTH-treated egg baits for removing ravens

Human-altered landscapes have provided resource subsidies for common ravens (Corvus corax) resulting in a substantial increase in raven abundance and distribution throughout the United States and Canada in the past 25 years. Ravens are effective predators of eggs and young of ground-nesting birds. During 2002–2005, we tested whether chicken egg baits treated with CPTH (3-chloro-p-toluidine hydrochloride) could be used to manage raven numbers in an area where raven depredation was impacting sharp-tailed grouse (Tympanuchus phasianellus columbianus) and greater sage-grouse (Centrocercus urophasianus) populations in Nevada. We performed multiple raven surveys at a treatment site and 3 control sites and used videography to identify predators and estimate egg bait consumption. We detected reductions in raven abundances over time at the treatment site during all years of this study and did not detect reductions in raven abundances at control sites. Videographic observations of egg consumption indicated that the standard 1:2 ratio (1 raven removed/2 eggs consumed) substantially overestimated raven take because nontarget species (rodents) consumed some egg baits. The technique described here likely will be effective at reducing raven densities where this is the intended management action.

Nest Predation of Greater Sage‐Grouse in Relation to Microhabitat Factors and Predators

ABSTRACT Nest predation is a natural component of greater sage‐grouse (Centrocercus urophasianus) reproduction, but changes in nesting habitat and predator communities may adversely affect grouse populations. We used a 2‐part approach to investigate sage‐grouse nest predation. First, we used information criteria to compare nest survival models that included indices of common raven (Corvus corax) abundance with other survival models that consisted of day of incubation, grouse age, and nest microhabitat covariates using measurements from 77 of 87 sage‐grouse nests. Second, we used video monitoring at a subsample of 55 of 87 nests to identify predators of depredated nests (n = 16) and evaluated the influence of microhabitat factors on the probability of predation by each predator species. The most parsimonious model for nest survival consisted of an interaction between day of incubation and abundance of common ravens (wravenXincubation day = 0.67). An estimated increase in one raven per 10‐km transect survey was associated with a 7.4% increase in the odds of nest failure. Nest survival was relatively lower in early stages of incubation, and this effect was strengthened with increased raven numbers. Using video monitoring, we found the probability of raven predation increased with reduced shrub canopy cover. Also, we found differences in shrub canopy cover and understory visual obstruction between nests depredated by ravens and nests depredated by American badgers (Taxidea taxus). Increased raven numbers have negative effects on sage‐grouse nest survival, especially in areas with relatively low shrub canopy cover. We encourage wildlife managers to reduce interactions between ravens and nesting sage‐grouse by managing raven populations and restoring and maintaining shrub canopy cover in sage‐grouse nesting areas.

As the raven flies: using genetic data to infer the history of invasive common raven (Corvus corax) populations in the Mojave Desert

Common raven (Corvus corax) populations in Mojave Desert regions of southern California and Nevada have increased dramatically over the past five decades. This growth has been attributed to increased human development in the region, as ravens have a commensal relationship with humans and feed extensively at landfills and on road-killed wildlife. Ravens, as a partially subsidized predator, also represent a problem for native desert wildlife, in particular threatened desert tortoises (Gopherus agassizii). However, it is unclear whether the more than 15-fold population increase is due to in situ population growth or to immigration from adjacent regions where ravens have been historically common. Ravens were sampled for genetic analysis at several local sites within five major areas: the West Mojave Desert (California), East Mojave Desert (southern Nevada), southern coastal California, northern coastal California (Bay Area), and northern Nevada (Great Basin). Analyses of mtDNA control region sequences reveal an increased frequency of raven 'Holarctic clade' haplotypes from south to north inland, with 'California clade' haplotypes nearly fixed in the California populations. There was significant structuring among regions for mtDNA, with high F(ST) values among sampling regions, especially between the Nevada and California samples. Analyses of eight microsatellite loci reveal a mostly similar pattern of regional population structure, with considerably smaller, but mostly significant, values. The greater mtDNA divergences may be due to lower female dispersal relative to males, lower N(e), or effects of high mutation rates on maximal values of F(ST). Analyses indicate recent population growth in the West Mojave Desert and a bottleneck in the northern California populations. While we cannot rule out in situ population growth as a factor, patterns of movement inferred from our data suggest that the increase in raven populations in the West Mojave Desert resulted from movements from southern California and the Central Valley. Ravens in the East Mojave Desert are more similar to ones from northern Nevada, indicating movement between those regions. If this interpretation of high gene flow into the Mojave Desert is correct, then efforts to manage raven numbers by local control may not be optimally effective.

Indirect Effects of Elk Harvesting on Ravens in Jackson Hole, Wyoming

Harvesting of marine and terrestrial animals by humans produces animal biomass byproducts that many scavenger species exploit. Effects of food byproducts from harvesting on the ecology of scavenger species has rarely been measured, especially in terrestrial systems. Such nutritional subsidization of scavengers needs to be monitored because increases in their populations may influence population dynamics of other species and alter natural community dynamics. I quantified effects of the distribution of elk (Cervus elaphus) gutpiles generated by an intensive harvest program in Jackson Hole, Wyoming, USA, on local raven (Corvus corax) foraging behaviors, daily and seasonal movements, and population distribution. During Jackson Hole's 2001 fall elk harvest, I found ravens to be the most abundant vertebrate species scavenging on monitored gutpiles, and the number of ravens I detected during fixed-width transect surveys positively correlated with concurrent, sympatric gutpile densities. I found raven abundance, estimated via point-count surveys in habitat-paired harvest zone and reference plots, to increase significantly in conjunction with the fall elk harvest only in the harvest zone plots. Furthermore, estimated raven abundance and nest density in the spring were significantly higher in the harvest zone plots than in the reference plots. Results indicate that in Jackson Hole, ravens exploit gutpiles provided by elk harvesting, daily raven distribution in the fall corresponds with the immediate distribution of gutpiles across the landscape, fall raven abundance is associated with the overall density of gutpiles in a given area in the fall, and spring raven abundance and nest density are associated with fall gutpile density. Collectively, these findings suggest that the high concentration of elk gutpiles in Jackson Hole is a significant supplemental food resource for ravens, and that wildlife harvesting in a terrestrial environment is capable of influencing the foraging behaviors, movements, and population dynamics of scavenger species. Wildlife managers must consider nontarget species when evaluating the efficacy of their regulatory programs and work to minimize unintended effects caused by wildlife management on the surrounding ecological community. Jackson Hole's elk population regulation program is a model for ungulate management due to its long-term success, while at the same time managers in Jackson Hole are continually addressing how their program may affect the surrounding ecological community and considering alternative management strategies to more effectively conserve the region's diversity. Results here provide baseline information on raven ecology in relation to Jackson Hole's current elk management program for comparison to other areas with intensive ungulate management programs, and for later comparison within Jackson Hole as strategies for managing its elk population change in the future. This study also draws attention toward monitoring effects of anthropogenic byproduct food resources that, despite their inconspicuousness in the literature, can substantially influence the ecology of opportunistic scavengers; and it points out several scavenger species other than ravens that also may be influenced by access to gutpiles or other anthropogenic foods that are abundant, reliable, and nutritious. Finally, having determined a clear link between elk harvesting and the population dynamics of ravens—an influential species in its ecological community—this study sets the stage for future research, testing the strength and extent of a trophic cascade that may be initiated by gutpile availability and propagated by increases in raven population density in Jackson Hole.

DRC-1339 use and control of common ravens

Author(s): Spencer, Jack O., Jr. | Abstract: The U.S. Fish and Wildlife Service (USFWS) and the Nevada Division of Wildlife (NDOW) have both observed an increase in the population of common ravens (Corvus corax) throughout Nevada. This increase is suspected to be the result of, at least in part, supplemental feeding sources (landfills, road kills, feedlots, etc.). The increase is of concern to wildlife managers because ravens are known nest predators, and in excessive numbers they could adversely affect a wide variety of game birds, including the sage grouse (Centrocercus urophasianus). During the spring in both 2000 and 2001, Wildlife Services (WS) was contracted to manage raven numbers in a critical sage grouse nesting area in northern Washoe County. The primary management tool used by WS was the registered avicide DRC-1339, because it can be selectively used on birds that feed on eggs. A prepared DRC-1339 solution was injected into hard-boiled chicken eggs and placed in artificial nest sites located throughout the project sites. Ravens foraging in the nesting area for sage grouse eggs found and consumed the treated eggs and died, thus selectively removing the nest-raiding birds from the immediate area of the grouse nesting sites. No long-term effect is anticipated on the raven population, because treated eggs were placed out only in the immediate area of the nesting grouse and only during the brief nesting period. The possibility of secondary poisoning resulting from DRC-1339 use is considered unlikely because the active ingredient, 3-chloro-p-toluidine hydrochloride, is broken down into a non-toxic substance and expelled prior to the bird expiring. Consumption of DRC-1339 results in death due to renal failure in avian species. Ravens found after treatment were monitored for the presence of West Nile virus titers.

Effects of Anthropogenic Food Sources on Movements, Survivorship, and Sociality of Common Ravens in the Arctic

AbstractWe investigated survivorship, movements, and sociality of Common Ravens (Corvus corax) exploiting concentrated food resources at a landfill in Greenland. From 1992–1995 we banded 383 ravens: 365 were captured at the landfill and 18 were banded in nearby nests. Thirty-nine ravens were recovered, most by shooting (87%). Mean number of days survived post-banding (494 ± 97) did not differ among age groups, but a higher proportion of juveniles was recovered. Ravens migrated west and south to the coast during winter. No difference existed among age groups in mean distance between locations of banding and recovery (151 ± 31 km). Number of ravens congregating at the landfill declined during the study, coinciding with a decrease in the local human population. Harsh winter climate, limited ice-free land, and abundant human refuse influenced raven use of the wilderness landscape by facilitating the formation of large, nomadic foraging groups.

Movement coordination and signalling in ravens ( Corvus corax ): an experimental field study

Vagrant non-breeding ravens frequently attract conspecifics to rich ephemeral food sources. There, grouping may allow them to overcome the defence of territorial breeders. Here, we focus on ravens making use of regular food supplies in a game park, where they divert food from the provision of park animals. We investigated if ravens foraging in the Cumberland game park (Grunau, Austria) are attentive towards one another when they experience some unpredictability in food provisioning. We confronted a group of 30–50 ravens with two different treatments. Ten minutes ahead of the feeding of either wolves or wild boars we showed buckets containing pieces of meat to the ravens flying overhead. In the reliable cue treatment (RCT), the meat was placed next to one of the two enclosures, whereas in the unreliable cue treatment (UCT), the buckets were placed simultaneously in front of both enclosures though only in one of the enclosures were the animals fed 10 min later. Thus, during RCT but not during UCT, ravens could predict where food would become available. Only during UCT, ravens moved in large groups between the two feeding sites. Many ravens moving at the same time in the same direction may indicate some co-ordination in space and time, which is most likely achieved by social attraction among individuals. Furthermore, the number of ravens approaching and leaving, respectively, a feeding site cross-correlated with a temporary increase in the rate of a food-associated call, the yell. This suggests that in addition to watching each other, calling may have contributed to group formation. Possible benefits of group formation during food inspection are discussed.

EFFECTS OF ANTHROPOGENIC FOOD SOURCES ON MOVEMENTS, SURVIVORSHIP, AND SOCIALITY OF COMMON RAVENS IN THE ARCTIC1

Abstract We investigated survivorship, movements, and sociality of Common Ravens (Corvus corax) exploiting concentrated food resources at a landfill in Greenland. From 1992–1995 we banded 383 ravens: 365 were captured at the landfill and 18 were banded in nearby nests. Thirty-nine ravens were recovered, most by shooting (87%). Mean number of days survived post-banding (494 ± 97) did not differ among age groups, but a higher proportion of juveniles was recovered. Ravens migrated west and south to the coast during winter. No difference existed among age groups in mean distance between locations of banding and recovery (151 ± 31 km). Number of ravens congregating at the landfill declined during the study, coinciding with a decrease in the local human population. Harsh winter climate, limited ice-free land, and abundant human refuse influenced raven use of the wilderness landscape by facilitating the formation of large, nomadic foraging groups.

Nest-Site Selection and Reproductive Success in Common Ravens

Studies of habitat selection by animals can be categorized in two ways: behavioral and evolutionary (Krebs 1994). Most studies of habitat selection consider the behavioral perspective whereby biotic and/ or abiotic components of the environment that appear to influence habitat use are identified, generally by comparing used sites with random or available sites (e.g. Mosher et al. 1986, Seamans and Gutierrez 1995). The evolutionary approach examines the effects of selecting particular habitats on an index of fitness, e.g. survivorship or reproduction (see Martin and Roper 1988, Petit and Petit 1996). If nest-site selection is a heritable trait, then natural selection should favor individuals that choose nest sites that confer greater reproductive success. Common Ravens (Corvus corax) are suitable subjects for examination of reproduction in relation to habitat characteristics owing to their variable clutch size, which ranges from three to seven eggs (Dunk et al. unpubl. data). Thus, in any one year, a relatively large range in number of young fledged is possible within a population, and it may be possible to detect a cline in reproductive success relative to nest-site characteristics. Common Ravens are widely distributed throughout North America and Europe. In western North America, ravens have been characterized as pests that easily adapt to human-modified landscapes (Butchko 1990, Boarman 1993, Marzluff et al. 1994). During the past 25 years, raven numbers have increased in many areas of the western United States (Boarman 1993, Dunk et al. 1994, Marzluff et al. 1994). Despite their ubiquitous nature, large numbers, and broad geographic range, little is known about many aspects of the breeding biology of ravens. In particular, very little has been published on raven nest-site selection. Ravens nest on many substrates, including cliffs (Ratcliffe 1962, White and Cade 1971, Hooper 1977, Skarphedinsson et al. 1990), highway overpasses and billboards (White and Tanner-White 1988), churches (Heinrich 1989), power poles (Knight and Kawashima 1993), and trees (Dorn 1972, this study), but nest-site characteristics have been quantified only for cliff nests (White and Cade 1971, Hooper 1977).

Common ravens and number and type of linear rights-of-way

We counted common ravens ( Corvus corax) during 1990 and 1991 in the Mojave Desert, California, to examine hypotheses relating to number and type of linear rights-of-way. First, we hypothesized that raven numbers would increase with increasing road traffic volume and traffic speed. Second, we hypothesized that raven numbers would show a positive relationship with increasing number of linear rights-of-way which ran in parallel. Our data did not support the first hypothesis but did support the second.

Common Ravens Are Attracted By Appeasement Calls Of Food Discoverers When Attacked

When adult territorial Common Ravens (Corvus corax) aggressively defend carcasses from vagrant immatures, both dominant and subordinate immature birds respond with begging postures and vocalizations. We demonstrated through experiments in an aviary complex that these vocalizations attract other ravens that then learn of new feeding oppor- tunities. Nearby free-ranging ravens also are attracted to begging vocalizations. Begging is most common when six or fewer immatures interact with adults. Typically, fewer than five birds are attracted locally to begging vocalizations, a number that is not sufficient to account for the large numbers of ravens that eventually assemble at a carcass. Most of the recruitment to carcasses, therefore, cannot be explained by attraction to local vocalizations alone. Received 21 October 1991, accepted 19 November 1992. THE EVOLUTIONARY significance of bird aggre- gations has long been of interest (Pulliam 1973). Numerous advantages of flocking have been suggested, including increased vigilance (Cara- co 1981), swamping of predators or competitors (Wallace and Temple 1987, Marzluff and Hein- rich 1991), and diversion or protection from predators (Kenward 1978). However, despite the wealth of information and theory on the po- tential evolutionary significance or adaptive- ness of bird aggregations, the proximate be- havioral mechanisms causing birds to form groups have been little investigated. There are numerous potential scenarios for how birds may aggregate. Solitary individuals may incidentally aggregate by using the re- source itself as a cue. Numbers of birds could then gradually increase simply because no mechanism exists to disperse them. Group size could also increase as naive birds follow others already at or on their way to the resource. When the advantages of individuals that follow also accrue to those already in the group, then the originally passive cues that are given by birds in the group and that the followers decipher should evolve to become amplified and/or to be more frequently given. A still further step in the evolution of group formation could in- volve the giving of specific cues or calls (Elgar 1986, Chapman and Lefebvre 1990) if any of the above mechanisms of group formation are in- adequate in generating groups. In the same way, when the signallers incur more costs than ben-

Movements and longevity of ravens in south-eastern Australia

Movements and longevity of Australian ravens (Corvus coronoides and C. mellori) are discussed on the basis of: (1) 11,558 birds banded 1953-1968,632 of which were recovered up to the end of 1968; (2) routine transect counts in two different areas; (3) data from colour-banded individuals. Three sorts of movements are shown, random dispersal, south-eastward migration, and the avoidance of coastal New South Wales. Most movements in excess of 10 miles involve non-breeding birds and account for the major fluctuations in raven numbers in any one district. C. mellori has a higher mean mortality rate (62.5%) than C. coronoides (51.O%), probably due to a more nomadic way of life.