Age ratio, crippling losses and factors affecting daily hunting bags of European Turtle-dove in Spain: Implications for sustainable harvest management of a declining migratory species

Knowledge of seasonal variation in hunting pressure and the demographic composition of hunting bags is likely to be important for the effective management of quarry species. Such knowledge is particularly important where regulatory mechanisms aim to avoid the over-exploitation of quarry species having unfavourable conservation status. We compiled information on the age composition of harvested European Turtle-doves (Streptopelia turtur), and the daily numbers of doves shot and retrieved from 68 hunting estates spread across four Spanish regions. We use these data to describe temporal variation, and identify factors affecting daily hunting bags, age composition and crippling losses. We found that more juvenile doves were hunted than adults (and more than expected in a stable population) especially at the beginning of the hunting season, suggesting greater vulnerability of juveniles to hunting. The number of doves hunted each day declined through the hunting season and increased with the number of hunters present. Crippling losses averaged 9.6 % of all doves shot; applying this rate to recent Spanish government hunting statistics suggests under-recording of approximately 90,000 doves annually for the entire country. Our data on age composition and crippling losses can serve as direct inputs into future models of sustainable harvest for Turtle Dove in Europe. Our results highlight the importance of improving knowledge about the variables influencing take at the hunting event level for designing more efficiency regulatory measures.

High density and successful breeding of Turtle doves Streptopelia turtur in Moroccan olive groves

Background

The turtle dove is a migratory species that has suffered a rapid decline principally across its Northern ranges, despite pronounced conservation measures. Consequently, it has been categorized as 'Near Threatened' in Europe. Degradation of breeding habitats and a decrease in food resources are listed as principal causes of this decline. Despite its importance, the productivity of the North African population is widely unknown. Here we present the first estimation of the density of the breeding population and the superior reproductively of Streptopelia turtur arenicola in Morocco and entire North Africa.

Methods

This study was carried out for two seasons 2018-2019 in the Saïss plain, central Morocco. Based on previous data, doves were monitored weekly, from early March to late August, in aquatic ecosystems (two dams and one river) and farmlands (cereals and orchards). The breeding population was censused using the "point-count" method, following a walked transect of 5 km in orchards, 7 km in cereal fields, and 3 km along the river. Equally, nests were searched in natural habitats counting riparian trees, forests, and ornamental trees, and in orchards based on the Common Birds Census (CBC) methodology, in which the singing doves, mating pairs, nesting, and/or feeding behavior were the most monitored signs to discover nests. In orchards, nests were searched line-by-line based on the rows of fruit trees. For each recorded nest, we note the breeding chronology, clutch size and incubation period, success and failure factors, dimensions, and vertical placement on trees. To evaluate the predictors of doves' occurrence, we noted at each site the presence of cereals, water, human disturbance, presence of nesting trees, and predators.

Results and Discussion

In total, 3,580 turtle doves (22.37 birds/ha), including 240 breeding pairs, were documented. Nesting occurred mainly in olive groves, cereals were used for forage, and aquatic ecosystems for water sources. The nesting period lasted from late April to July (last fledglings). All nests were located on olive trees at a height of 225.30 ± 48.87 cm. The clutch size was 1.98 ± 0.13 (laid eggs/built nests), the incubation period lasted 14.16 ± 1.32 days, and the rearing period lasted 16.54 ± 1.76 days. The breeding success among the 240 monitored nests accounted for 73.84% during the nesting phase and 87.42% during the incubation phase; 71.5%% of nestlings have fledged, which is the highest success rate for turtle doves in Europe and Northwest Africa. Clutches were aborted mostly due to predation from snakes (7.5% of nests, 16.12% of eggs, and 5.63% of chicks), nest desertion (9.16% of nests and 5.37% of eggs), and marginally by the destruction of nests through farming activities. These findings are important for conservation plans, to restore turtle doves' habitats in Europe, where the species is widely declining.

Hunting Levels of Turtle Dove (Streptopelia turtur) at Sites Where Food Is Provided: Implications for Sustainable Harvesting

Simple Summary

The European turtle dove (Streptopelia turtur) is an important gamebird in south-western Europe, and in some areas a significant proportion of hunting grounds conduct targeted management aiming to increase its breeding densities and hunting opportunities, mainly through food provision. Using harvest data from managed grounds, we estimated the productivity (juvenile/adult ratio), the harvesting levels and the local turtle dove abundance before the hunting season, the latter being compared to the number of birds observed by hunters in food plots. Our research found high values of productivity and significant differences between the estimated abundance and the number of birds observed by hunters, which suggests that in a high proportion of grounds, the latter method may have led to bird overestimation and overharvesting. As managed grounds for the turtle dove may increase the productivity and recruitment of the species, it is crucial to ensure sustainable harvesting through (1) bird monitoring based on transects to calculate abundance and (2) promoting regulations to adjust the number of hunting days.

Abstract

In some regions of Spain, hunting grounds conduct management targeting the European turtle dove (Streptopelia turtur), a commonly hunted species, and unsustainable harvesting levels at these sites have been identified as one of the factors responsible for the species’ decline across its range. In hunting grounds where food was provided, we estimated the local turtle dove abundance before the hunting season, productivity (juvenile/adult ratio) and harvesting levels using harvest data from managed grounds over 4 years (2009, 2015, 2019 and 2020). Compared to previous research, a higher productivity value was found (median 1.67, range 1.24–4.15) in grounds providing more food for a longer period. We calculated that the harvesting rate should not exceed 37% of the estimated turtle dove population size (35–45%). Significant differences were found between the estimated local turtle dove abundance using a removal sampling protocol and the number of birds observed by hunters before the hunting season, which suggests that in a high proportion of grounds, the latter method may have led to bird overestimation and overharvesting. Our research supports the current European Union’s harvest management plan to promote sustainable hunting in grounds where targeted management is conducted.

European Turtle Dove Population Trend in Greece Using Hunting Statistics of the Past 16-Year Period as Indices

The European turtle dove is an important game bird for the hunters in Greece, which is one of a few European countries where its hunting is allowed. The sustainability of the species’ hunting in Europe is discussed during the last several years due to declines in its population, which forced IUCN to classify it as vulnerable. In Greece, its harvest takes place from 20 August and lasts as long as the presence of the species in the country (mid-October). The ARTEMIS project is a Greek statistical database of hunting characteristics, as revealed by questionnaires distributed to hunters. Statistical indicators such as hunting opportunity and hunting harvest are considered in the literature as reliable to show the population trend of a game species. Therefore, in the present research, hunting statistics are used to determine the population trend of the European turtle dove in Greece. State-space modeling was the main procedure used, a method which allows us to deal with errors that exist from hunting bag data or hunting opportunity data assuming that on average the under and overestimations will be equal. The results of the modeling analysis show a stable trend of the variables used, i.e., hunting opportunity, hunting harvest, and juveniles to adult’s ratio. Additionally, the hunting sustainability index showed that the sustainability of the species is improved annually, as a slight positive trend is revealed. This is in favor of the species, if it is considered that the actual percentage of the turtle dove population harvested is lower, since not all doves are encountered by hunters. It is concluded that for the period 2004/05–2019/20, as indicated by the hunting statistics, the population trend of the European turtle dove in Greece was stable and its harvest sustainable.

Estate-level decision-making and socioeconomics determine annual harvest in the European Turtle-dove in central Spain

Designing evidence-based policies that regulate harvest levels is essential to avoid unsustainable hunting. This requires a good understanding of the relationship between bag sizes and regulatory mechanisms of harvest, and particularly of how these mechanisms are implemented locally and how they vary between game estates. The European Turtle-dove (Streptopelia turtur) has decreased by 30-49% since the late 1990s. The three main identified threats for the species are habitat loss, illegal killing and unsustainable legal hunting. We assessed how turtle dove estate-level harvest varies in relation to hunter density, number of hunting days, the adopted hunting method, game management intensity and the economic investment of the estate. Additionally, we assessed whether estate-level harvest had declined concomitantly with the population decline, and whether trends had been similar in relation to hunting method. We analysed Hunting Management Plans and Annual Hunting Reports of several thousand estates in central Spain, one of the main breeding and hunting areas of the species. Annual estate harvest was positively associated with hunter density, and was higher on estates that offered fixed-position hunting compared to those that only provided walked-up shooting. Importantly, these decisions are made by managers at the estate level and are not directly regulated by policy. We also found that more turtle doves are harvested on estates that invest more money in management, suggesting that the socioeconomic characteristics of the estate also influence local decisions on harvest intensity. Average annual estate-level harvest declined by 27% between 2007 and 2018, accompanied by a switch from fixed-position to walked-up hunting practices. Our study indicates that reducing hunting density or the number of fixed-position hunting days may be the most efficient ways to reduce turtle dove harvest, and that factors influencing estate-level decision-making have to be understood if reduction of hunting pressure in declining species is sought.

A Stepwise Assessment of Parsimony and Fuzzy Entropy in Species Distribution Modelling

Entropy is intrinsic to the geographical distribution of a biological species. A species distribution with higher entropy involves more uncertainty, i.e., is more gradually constrained by the environment. Species distribution modelling tries to yield models with low uncertainty but normally has to reduce uncertainty by increasing their complexity, which is detrimental for another desirable property of the models, parsimony. By modelling the distribution of 18 vertebrate species in mainland Spain, we show that entropy may be computed along the forward-backwards stepwise selection of variables in Logistic Regression Models to check whether uncertainty is reduced at each step. In general, a reduction of entropy was produced asymptotically at each step of the model. This asymptote could be used to distinguish the entropy attributable to the species distribution from that attributable to model misspecification. We discussed the use of fuzzy entropy for this end because it produces results that are commensurable between species and study areas. Using a stepwise approach and fuzzy entropy may be helpful to counterbalance the uncertainty and the complexity of the models. The model yielded at the step with the lowest fuzzy entropy combines the reduction of uncertainty with parsimony, which results in high efficiency.

Modelling European turtle dove (Streptopelia turtur L. 1758) distribution in the south eastern Iberian Peninsula

The European turtle dove population and breeding range has declined sharply in Spain. This study reanalyses data from the Atlas of Breeding Birds in Alicante (SE Spain), aiming to identify the main variables related to its occurrence and abundance. We used hierarchical partitioning analysis to identify important environmental variables associated with natural vegetation, farming, hydrological web, anthropic presence, climate, and topography. Analysis combining the most explicative variables of each group identified the mixture of pines and scrubland in the semiarid areas and the length of unpaved roads as the most important variables with a positive effect on occurrence, while herbaceous crops and scrublands in dry ombrotype climate areas had the most important negative effect. Abundance was related only to the availability of water points. We discuss the implications of these findings for habitat management in conservation of this species.