Peregrine Research Articles

A Large Aggregation of 50 Peregrine Falcons (Falco peregrinus) During Migration in the Western Gulf of Mexico

In October 2017, we opportunistically observed up to 50 Peregrine Falcons (Falco peregrinus) on a ship moored in the western Gulf of Mexico. All birds we aged were juveniles, and they hunted from the ship, frequently perching extremely close to one another (<1 m apart) on cables. Both the number of birds and also the very short inter-individual distances when perching make these observations unusual among the published reports for this species.

Genetic variability in Peregrine Falcon populations of the Western Palaearctic region

Abstract We analysed variation in ten polymorphic microsatellite loci and a portion of cytochrome b gene of mitochondrial DNA in 65 samples from four populations of Peregrine Falcon (Falco peregrinus peregrinus and F. p. brookei) breeding in Northern and Southern Italy, Northern Spain and the Czech Republic to assess genetic diversity in the poorly investigated Western Palearctic region. We added to our cytochrome b sequences a dataset of previously published mtDNA sequences of other populations and subspecies to outline genetic variation in the region on a worldwide basis. Regarding mtDNA we identified 12 haplotypes from our 65 Peregrine Falcon samples, nine of which were new and three already known. The 52% of our samples, including all Italian and Czech specimens, belonged to the previously identified HI haplotype, another 22% of the samples, most of which were from Sicily, showed the new H1 haplotype, while the remaining 26% of the sample partitioned among the other 10 haplotypes. Allelic patterns and genetic structuring of microsatellites were similar to those of other European populations. Genetic differentiation in both mtDNA and microsatellites loci is almost absent and it is not possible to distinguish geographical groups according to taxonomic designation at the subspecies level.

Onset of natal dispersal in Peregrine Falcon from Mediterranean islands (Italy)

Abstract Basic information on natal dispersal of Peregrine Falcons is virtually lacking in Europe, despite increased attention on this species, and the sensitivity of this stage in the Peregrines’ life history. In this study, we collected satellite telemetry data during the onset of natal dispersal of 19 Peregrine Falcons tagged in Sicily and the Aeolian archipelago (Italy). We divided the onset of dispersal into the following 3 periods: post-fledging dependence period (PFDP), wandering, and wintering. PFDP lasted on average 47±16 days, during which young peregrines moved very little (0.167 km), and explored small areas (0.226 km2) far from the nest cliff, and showed no sex differences. The wandering phase was highly individualistic, with median net displacements of 23.97 km. Both PFDP and wandering bearings were oriented towards NNE-ESE. Only five individuals went sporadically outside the island borders. During their first winter, Peregrines had a mean home range of 135.65±82.31 km2 spatially scattered across Sicily and mainly composed of open habitats, like cereal steppes, arboreal crops and agri-mosaics. Individuals had a dissimilar assortment in habitat composition, however the urban habitat was the most selected and the woodland the least. At night, during both wandering and wintering phases Peregrines used rocks, cliffs and electricity pylons in frequencies not statistically different between sex, phase and type of roost. Only two individuals had significant use of pylons and one of rocks. The multifaceted framework of Peregrine Falcon’s natal dispersal was described here for the first time in a Mediterranean population.

Diet of Peregrine Falcons (Falco peregrinus) in relation to temporal and spatial variation in racing pigeon availability in Wales

Abstract The relative frequency of Common Pigeons Columba livia in the diet of Peregrine Falcons differed across three areas of south-central Wales in line with racing pigeon availability. Peregrines exhibited a functional response to spatial and temporal availability of racing pigeons. During the pigeon-racing season (April–September), pigeons comprised 63% of kills in South Wales where pigeons were most available, 43% in the Brecon Beacons with intermediate availability and 30% in Central Wales, where availability was lowest. The corresponding values outside the pigeon-racing season were 18%, 6% and 5% respectively. We estimate that 92% of pigeons killed by Peregrines were racing pigeons, 7% were feral pigeons and the remainder were other domestic pigeon varieties.

Breeding population of Peregrine Falcon (Falco peregrinus) in Lazio, Central Italy: 1983–2017

Abstract In 1983–1984 the nesting population of Peregrine Falcon (Falco peregrinus) in Lazio was estimated to 25–30 pairs located mainly in the limestone massifs of the Southern Anti-Apennines and the Ponziane Islands. The monitoring carried out in the following years showed a steady increase in population size and range. In 2014–2017, the breeding population was 166–193 pairs distributed over most of the regional territory. In four regional macro-geographic areas characterized by different morphologies, lithological and landscape typologies, the density was calculated by NND method, which varied from a minimum of 0.90 to a maximum of 1.77 pairs/100 km2; average distance between sites from 3848.18 m to 6526.87 m. The urban population of Rome increased from the first nest found in 2001 to 15 currently breeding pairs; the first artificial nest was discovered in 2001 on the building, currently 14 are known. At present in Lazio 16 nests are located in quarries. In the years 2008, 2014, 2015 and 2016, the fledging rate registered was 2.26 (SD = 0.94; bp = 153).

Population trends of the Peregrine Falcon in Switzerland with special reference to the period 2005–2016

AbstractWe study population trends of the Peregrine Falcon(Falco peregrinus)in Switzerland with special reference to the development since 2005 and three study areas, South West Switzerland (4,993 km2, 1960–2015), the Northern Jura mountains (3,270 km2, 2005–2015) and the Canton of Zurich (1,748 km2, 2002–2015). We used dynamic occupancy models, which allow the territory-specific extinction and colonization parameters – the demographic rates (at the territory level) underlying a population trend – to be estimated. The Swiss peregrine population has developed in line with trends observed in many other countries and regions in North America and Europe: after the pesticide-induced collapse between the 1950s and 1970s, the population largely recovered up to the turn of the millennium. However, in recent years, we detected significant declines again: in SW Switzerland, the population decreased from 51 to 33 pairs during 2008–2015 (-35%), in the N Jura from 70 to 40 pairs during 2009–2015 (-43%) and in Zurich from 6–7 to 2–4 pairs during 2010–2015 (-50%). In the same time, the local extinction rate in the three study areas (more than) doubled from (0.05) 0.1 to 0.2, while the colonization rate dropped from 0.3 to 0.1 in one of the areas, while no change was detectable in the other two. We discuss two factors responsible for these strong, recent declines of Swiss peregrines: (1) predation by Eagle Owls(Bubo bubo)and (2) direct and illegal persecution by humans. In addition to these two factors, growing human disturbance (e.g. through climbers, bird photographers, paragliders, hikers, geocachers, etc.) and fatalities due to collisions with man-made structures (power lines, glass, wind turbines, etc.) are also suspected to contribute to the population decline.

Extreme territorial aggression by urban Peregrine Falcons toward Common Buzzards in South-West England

Abstract Peregrine Falcons (Falco peregrinus) breeding on a city centre church in Exeter, in the south-west of England, have been studied in detail since first occupation in 1997. During this period, changes in both male and female falcons have been recorded. Following the arrival of a new female Peregrine in 2009, a dramatic change in behaviour towards Common Buzzards (Buteo buteo) on passage over the city was noted. Buzzards flying over Exeter are attacked by the falcons, especially so when in proximity to the church. We have attempted to document these attacks through our own observations, with additional information from local residents and wildlife organisations. Further records have come from veterinary surgeries and wildlife rehabilitators regarding injured buzzards found in the city. This paper documents the extreme levels of territorial aggression as demonstrated by the pair of Peregrines during cooperative attacks on Buzzards. We reveal this unique interspecific behaviour by summarising the number, frequency, timing and outcome of attacks undertaken over an eight-year period. We describe and illustrate the strategy employed by the Peregrines during a typical attack, plus consider implications on breeding productivity and the future scenarios should one of the current pair be replaced.

A 20-year study investigating the diet of Peregrines, Falco peregrinus, at an urban site in south-west England (1997–2017)

Abstract Until relatively recently Peregrines have been regarded as a rural bird. As their populations have increased over the past 20 years, Peregrines have increasingly become urban birds. One of the earliest locations to be occupied by Peregrines in the UK was on a church in Exeter, in the county of Devon. Over the past 20 years we have studied their diet, collecting prey remains on a regular basis. The results reveal that Feral Pigeons Columba livia comprise one third of the diet by frequency and just over half of the diet when measured by mass. The remainder of the diet comprises a wealth of other species including wading birds, other doves and pigeons, ducks, gulls and terns, and rails. A selection of species eaten by the Peregrines reveal that they are hunting at night, taking certain wading birds, rails and grebes, that would be difficult to catch by day and are known to migrate at night. This study is the most comprehensive to date and reveals that while the Feral Pigeon is an important part of the diet, contrary to public opinion, it is by no means the only species that Peregrines eat. In fact, the remaining half of the diet, by mass, comprised 101 other species of bird and three species of mammal. Such dietary studies help dispel myths about peregrines feeding habits and ensure that their conservation and protection is based on evidence.

Monitoring of Peregrine Falcons in the Ariège Pyrenees and Toulouse, Midi-Pyrénées region, France

Abstract Since the 1980s, the volunteers of the ornithological group of the Nature Midi-Pyrénées association have been monitoring the Peregrine Falcon (Falco peregrinus) population in the Ariège Pyrenees and in the Toulouse agglomeration. The data collected over the last 30 years show stability of the Ariège population: little variation has been observed in brood size, occupation rate of the sites or reproductive success. Only the increasing number of known nesting sites is significant, due to better knowledge of the territory by observers over time. In 2017, the breeding population was estimated to be 24 pairs. Urban monitoring proved the presence of individuals in passage, wintering or resident in Toulouse. Since 2002, downtown Toulouse has been visited by several individuals of both sexes and interactions between males and females have been observed since 2005. Despite the multiplicity of possible eyries or nesting sites in Toulouse, and the massive presence of Peregrine Falcons and dedicated bird watchers, no case of breeding has been reported. In addition to monitoring, measures to protect and support the presence of the species have been put in place. In the Pyrenees, in the light of the growth of human activities near nesting sites, some sites are now subject to official protective measures, coupled with constant vigilance and awareness. In Toulouse, to encourage the breeding of the individuals present, two nesting boxes were installed in 2016, on two buildings frequented by a female and a male. In 2017, a first attempt to reproduce in one of these installations confirmed the value of such developments in urban areas.

Mercury contamination in Peregrine Falcons (Falco peregrinus) in coastal Washington, 2001–2016

Mercury contamination in Peregrine Falcons (Falco peregrinus) in coastal Washington, 2001–2016

Population trends of Peregrine Falcon in Northern Spain – Results of a long-term monitoring project

Abstract We monitored Peregrine Falcon (Falco peregrinus) population in Bizkaia, Northern Spain, during two decades (1998–2017). Our population increased from 34 to 47 territorial pairs, as did other European populations until the first years of the 21st century, and then declined until 34 territorial pairs in 2017. The combination of catastrophic events (Prestige oil spill), increasing rain in winter and spring, and direct and indirect mortality factors significantly affected incubation onset, productivity and population stability, which in turn could impact on the floater population. Rain in February significantly affected incubation onset, which showed a slight positive trend during the last decade. Juvenile females laid 12 days later than adults, and each adult female started incubation in the same dates every year. However, the proportion of juvenile females did not significantly increase as might have been expected. Moreover, productivity was inversely related to incubation onset dates. Rain in April and May also affected productivity, and combined with short term extreme weather events determined a decreasing productivity during the last decade. Moreover, apart from human persecution (which caused 40.30% of the known deaths of Peregrines), we found 18 cases of breeders affected by infectious diseases, also related to weather. The combined effects of these factors, and the low availability of adequate nesting sites, negatively affected (i) territorial populations, (ii) productivity, and (iii) floater population, which in turn also determined territorial population and productivity.

Nesting habitat selection and distribution of an avian top predator in the Canadian Arctic

Detecting and planning for ecosystem changes from climate and land-use alteration is limited by uncertainty about the current distribution of many species. This is exacerbated in remote areas like the Arctic, where the impacts of climate change are the strongest and where industrial exploration and development are expanding. Using remotely-sensed environmental information and known nest sites, we estimated the breeding distribution and habitat selection of the peregrine falcon (Falco peregrinus) throughout most of Nunavut, a massive northern Canadian territory (&gt;1.8 M km2) encompassing ∼15% of the world’s tundra biome. Our results show that peregrine falcons selected features of prior known importance such as rugged topography, but also sites with higher than average summer temperatures, more productive land classes, lower mean elevations, and lower mean summer precipitation. Our model identifies several areas of high relative probability of peregrine occurrence, some of which were unrecognized to date. Some of these areas may be targets for future industrial developments and are located in an area where some of the fastest climate changes are expected. Our model will allow managers to identify the areas that could be the most critical for monitoring in the context of future development and climate change.

The Danish Peregrine Falcon population: Reestablishment and eggshell thinning

Abstract Denmark being a country with only a few suitable steep nesting cliffs has only harboured a small population of Peregrine Falcons (Falco peregrinus) in historic time. In the previous century, the population gradually declined due to persecution, egg and young collection, and pollution. The last breeding attempt in the 20th century occurred in 1972 in southeastern Denmark. No new breeding attempts were recorded in Denmark until 2001 but since then the population has gradually increased – most rapidly since 2012 – to a peak of 24 territorial pairs in 2018; some of them breeding on man-made structures (nest boxes at bridges and power plants). Here we update the information on the reestablishment of the Peregrine Falcon in Den-mark, including origin and dispersal, reproduction, and eggshell thinning.

Raptors are still affected by environmental pollutants: Greenlandic Peregrines will not have normal eggshell thickness until 2034

Abstract The DDT-induced effects, eggshell thinning and breeding failure in Peregrine Falcon (Falco peregrinus) populations were reverted with restrictions on the use of the compound from the 1970s, and in most studied populations, the eggshell thickness is back to normal. In Greenland, a previous study of eggshell thinning in Peregrines found that shells had not yet reached pre-DDT levels. In this study, we extend the time series and reinterpret shell thinning data for 196 clutches covering a 45-year time span (1972–2017). There was a significant (P&lt;0.001) increase in the eggshell thickness of 0.23% per year. This corresponds to a change in eggshell thinning from 14.5% to 5.4% in 2017 compared to the pre-DDT mean. With the current rate of change, pre-DDT shell thickness is predicted to be reached around the year 2034. However, a few clutches are still below the critical limit. The relatively slower recovery of the shell thickness in the Greenland population is likely indicative of the slower phasing out of DDT in the Greenlandic Peregrines’ wintering grounds in Latin America. The shell thinning in the Greenlandic population probably never crossed the 17% threshold associated with population declines, contrary to the populations in many other parts of the world.

Mackenzie River Peregrine Falcon Surveys 1966–2018

Abstract The author with assistants monitored the breeding distribution of Peregrine Falcons (Falco peregrinus) along the length of the Mackenzie River, Northwest Territories, Canada from 1966 to 2018. This river traverses a thousand miles (1600 km) of the western Canadian Arctic from Great Slave Lake to the Beaufort Sea and roughly parallels the eastern slope of the Mackenzie Mountain cordillera between latitudes 61 degrees N and 68 degrees N. All potential nest sites have been checked on each survey and counts of nest sites occupied (at least one bird seen) decreased from the count of 12 sites in 1966 to the lowest count of 7 in 1972. In 1990 the count was 37 and up to 2018 the highest count was 75 in 2010. A count of nest sites successfully producing young was variable with a low of 5 in 1972 to a high of 58 in 2011. Production of young averaged 2.43/successful site from 1990 until 2018 (excluding 2012). Production of young averaged 1.4/occupied site over this period. Recent increases in availability of passerine prey because of widespread fires in the last decades are felt to be the latest phenomena affecting these birds (pers.obs.) Prey utilized by Peregrines was studied over a period of four years and passerines composed 20% of their diet. Two species Lesser Scaup (Athya affinis) and Lesser Yellowlegs (Tringa flavipes) formed 25% of their diet.

The Peregrine population study in the French Jura mountains 1964–2016: use of occupancy modeling to estimate population size and analyze site persistence and colonization rates

AbstractWe summarize key results of the first 53 years of one of the longest-running avian population studies in the world, on the Peregrine Falcon(Falco peregrinus),in the French Jura mountains (12,714 km2), launched in 1964. A total of 449 cliff sites in 338 potential Peregrine territories were surveyed: 287 (85%) of these territories were occupied by an adult pair at least once, while in 51 (15%) we never detected an adult pair. Most sites were visited several times during a breeding season to survey occupancy and later fecundity, but the proportion of sites visited was highly variable over the years. We highlight the power of the Bayesian implementation of site-occupancy models (MacKenzieet al.2002, 2003) to analyze data from raptor population studies: to correct population size estimates for sites not visited in a given year and for the biasing effects of preferential sampling (when better sites are more likely to be checked). In addition, these models allow estimation and modeling of the site-level persistence and colonization rates, which can provide important clues about drivers of population dynamics, even without individually marking any birds. Changes in the dynamics rates may serve as early-warning signals for subsequent population declines.Since 1964, the observed number of adult pairs varied between 17 in 1972 and 196 in 2008, but the proportion of sites visited increased from 43% in 1964 to 80–90% after 2002. Hence, this raw population total must be an underestimate. We found strong evidence for preferential sampling in our study. Correcting for this, we estimated 56 pairs in 1964, after which the population dropped to a minimum of 18 in 1972, but then recovered rapidly, leveling off somewhat around 1995 and reaching a maximum of 200–210 adult pairs during 2000–2012. This was then followed by a decline to 170–190 pairs. In any one year, the raw counts underestimated the true population size by 5–39% (mean 11%), due to sites not being visited (this correction ignores imperfect detection though). Site persistence rates declined from 78% to less than 60% during 1967–1972, and then increased rapidly to over 90% during 1980–1990, suggesting that once pesticide effects vanished, individual survival probability increased rapidly and as a consequence also site persistence. Since the 1990s, persistence has declined slowly, which may indicate decreasing adult survival. In contrast, colonization rates increased steadily from about 3% in the early years to maxima of 46–49% during 1994–2001, but declined thereafter and currently reach about 33%. Taller cliffs had greater persistence and colonization rates than medium or small cliffs.Both the decline in colonization and in persistence rates during the last 15 years may reflect density-dependence, predation by the expanding European Eagle Owl(Bubo bubo)population, human persecution or any as yet unknown factors. Importantly, we note that both persistence and colonization rates began to decline many years before the recent population decline became apparent. Thus, analysis of population studies using dynamic occupancy models can provide early-warning signals for future population declines. Our study demonstrates the benefits of modern analytical methods that can correct for several key deficiencies in probably all raptor population studies: incomplete coverage of sites and imperfect detection (though we only dealt with the former here). Occupancy models, possibly accounting for preferential sampling, appear to represent the logical analytical framework for abundance in raptor population studies.

Extreme weather affects Peregrine Falcon (Falco peregrinus tundrius) breeding success in South Greenland

Abstract In order to better understand the potential effects of climate change on the Peregrine Falcon, we investigated the relationship between extreme weather events and Peregrines’ breeding success in South Greenland. We defined three variables – number of days with extremely low temperatures, extreme precipitation, consecutive rainy days – and an additive variable, total days with extreme weather, and tested their relationship with Peregrines’ breeding success (measured as young per site and nest success) over a 33 year study period. Breeding success was negatively influenced by the number of days with extreme weather and extremely low temperature. The strongest relationship found was total days with extreme weather in the entire breeding season, which explained 22% and 27% of the variation in nest success and young per site, respectively. The number of days with extreme weather in our study related to fluctuations in the North Atlantic Oscillation (NAO). Thus, with a strengthening of the NAO, linked to climate change, more extreme weather may occur in the Arctic and induce increased variation in Peregrines’ breeding success. Our data did not allow us to pinpoint when in the breeding cycle inclement weather was particularly harmful, and we recommend finer-scale research (e.g. automated nest cameras) to better monitor the species-specific effects of rapidly changing climate.

Long-term monitoring of a successful recovery program of Peregrine Falcons in Virginia

Abstract The Peregrine Falcon (Falco peregrinus anatum) was believed to be extirpated as a breeding species in Virginia by the early 1960s. An aggressive restoration program was initiated in 1978 that involved the release of captive-reared birds totaling 115 on the Coastal Plain (1978–1985) and 127 in the Mountain physiographic region (1985–1993). The first occupied territory was established and the first breeding attempt was documented in 1979 and 1982, respectively. We have monitored the size, distribution, reproductive rate, and substrate use of the resulting breeding population (1979–2016). The population proceeded through an establishment phase (1979–1993) driven by releases with an average doubling time of 3.8 yrs to a consolidation phase (1994–2016) with an average doubling time of 23.1 yrs. The state supported 31 breeding pairs by 2016. Per capita reproductive rates have increased significantly over the study period from 0.89 (1979–1993) to 1.86 (1994–2016). Average nesting success increased from 67.1% to 82.7% over the same period. Nesting attempts (n = 469) have been documented on dedicated peregrine towers (52.1%), bridges (26.1%), buildings (4.1%), and various man-made structures (13.0%) with only 4.7% documented on natural cliffs. The population appears to be self-sustaining with reproductive rates exceeding 1.5 young/pair every year since 1999. An ongoing management concern is that only 8.9% of known territories (n = 45) identified since introductions and 4.7% of documented breeding attempts (n = 469) have occurred within the historic mountain breeding range.

A summary of intentional poisoning of Peregrine Falcons in Switzerland during the last decade

Abstract In May 2011, a webcam in Zurich, Switzerland, registered the sudden death of a Peregrine Falcon. Analyses revealed that poison had been applied to the nape feathers of the pigeon captured by the bird. This case really raised the awareness of Peregrine Falcon poisoning by pigeon fanciers in Switzerland. BirdLife Switzerland, with the help of numerous partners, started researches on the subject that pigeon fanciers began a “war” against Peregrine Falcons and other raptors. Between 2006 and 2017, BirdLife Switzerland listed 7 cases of proven intentional poisonings of birds of prey where analyses confirmed the use of poison; and 19 suspected cases with the presence of dead pigeons and birds of prey simultaneously or other suspicious deaths in Switzerland. Three decoy pigeons with poison on the neck could be secured before they were captured by the target species. Two pigeon fanciers who used poisoned pigeons were convicted in 2016 and 2017. Although the numbers of proven and suspected cases are still low, we believe that the phenomenon may be much more widespread. We think that the poisoning may have a negative effect on the population of the Peregrine Falcon in Switzerland.

Restoration of the tree-nesting Peregrine Falcon (Falco peregrinus) population in the Volga-Ural Region

Abstract We have applied the method of a forming tree-nesting behavior pattern in the chicks of the cliff-nesting Peregrine Falcon. In June 2016 and 2017, in the Southern Ural Mountains and Bugulma-Belebey Upland, we discovered four nests of Peregrine Falcons, which were threatened by destruction due to various anthropogenic and biological factors. For preventing the death of the broods, the chicks were transferred from the occupied nesting niches in the rock cliffs to nesting platforms. On nesting platforms they spent from 3 to 12 days where they were fed by adults regularly. All four broods (9 young) flew out successfully and demonstrated typical behavior for the Peregrines of their age. Adults fed fledglings and taught them to hunt.