Birds' surveys are used to give reliable approximate or index of the size of the population of a definite species due to various reasons within a given area (Gitzen 2012). Birds' surveys are often conducted to assess habitats for suitability to support breeding and at times wintering birds species and record incidental bird citing during visits. Special emphasis is often placed on the suitability of the site for given species and due to conservation concerns. After an initial assessment, further surveys may be required for obtaining detailed account of birds species of birds and communities in key habitats areas. The counts help to track changes in birds’ populations when repeated at regular intervals. This can help to identify the population trends over time (monitoring). Before one rushes to undertake a survey, a monitoring program should be prepared (Budnitz et al. 2009).
Breeding birds surveys consist of two to ten visits recording as well as mapping all birds' species seen and/or heard along with any relevant behavior such as gathering nesting material, territorial calling, fighting and feeding young one. These surveys are conducted using BTO undertaken between April 1st and June 30th (Budnitz et al. 2009).
Specialized birds surveys are undertaken using techniques for special species such as Barn Owls and Black Redstart to obtain more population estimates, important habitats such as estuaries (Hill 2010). Wintering birds surveys entail at least four visits taken between September and March to record notable assemblage of feeding and roosting birds species. Nests can also be searched for by hands especially immediately prior to development activities. This is often the last resort. However, this is only practical for small areas of scrub and individual trees and bushes. Number of visits relies on the size and importance of the key birds habitats identified in previous surveys. True census counting is easier to conduct with rare birds with restricted ranges since in this case sampling might record too few birds to produce reliable estimates unlike for more common species whereby counting a whole area would be expensive (Gitzen 2012).
. This could be a grid square, precise location boundaries and boundaries from maps. Subdividing an area into a large number of grid squares on the map may seem statistically sound though it is impractical and very difficult to use (Hill 2010). Hence, use of individual plots of varied sizes is advisable (Hill 2010).
Specially tailored (generic) methods such as mapping and transect are recommended for same species. Accuracy, precision and bias are another set of important parameters to consider in conducting birds' surveys. The high-risk design should often revolve around accuracy and precision to reduce bias. Ensuring the accuracy is technically difficult and prohibitively expensive as it would require intensive work in very small areas, which are time-consuming. Bias occurs when estimates are systematically larger or smaller than the true value. Different methods could result into bias. Inappropriate field method such as poor timing can lead to biased data. All potential sources of bias should, therefore, be identified, and survey methods be standardized to where appropriate to reduce bias. Moreover, no assumption should be made that a particular survey is free of bias.
For mammals, a number of factors should be considered when designing wildlife survey. That is; it should be appropriate to the project objectives, based on sound scientific and statistical principles, be kept to the justified number. Practical skills must be met by the surveyor (Budnitz et al. 2009). The type of appropriate survey method and sampling design will thus depend on the objectives of the study, target species and time available for surveys. While many survey objectives are possible, for the purpose of inventory, these may be generalized as objectives to estimate population distribution, relative and absolute abundance. Hair tube traps can be used, and their floors should be free of adhesive tape to prevent small frogs and lizards becoming stuck, never attempt to pull it off since it can lead to damage of its skin. Slope hair tubes with entrance pointed slightly downwards to allow drainage. If there is no proper drainage, the trap may not work
The areas for abundance and composition surveys are in most cases arbitrary and can, therefore, be as large as Eco provinces or as small as a stand of trees. To identify a study area, the project area must be stratified or classified by habitat category and survey work concentrated in the areas most likely to provide data relevant to objectives. This requires knowledge on target species, natural history and physical limiting factors such as access. The sample units for small mammals should transect line and/or trapping grid, contrary to the individual animal within the population. Similarly, even though individual traps are used for individual animals species, sampling units consist of many of traps laid in a particular configuration or pattern defined by the objectives or aims of the survey. Four capture stations per home range with the spacing of approximately 15m between capture stations are recommended.
Climate is an important factor to consider as small mammals fluctuate annually with low populations occurring late in the winter unlike high populations, which occur after the breeding season (Gitzen 2012). Sampling in late summer or early after breeding season when populations are at the yearly maximum will result into the likelihood of capturing any species. In the case of the presence/not detected survey meant for documenting habitat associations, sampling should be done earlier within the year before juvenile dispersal. A time individuals are most likely to be present within their preferred habitats. Capture sessions should occur at least twice a year during the active season (May to October) in case relative abundance is to be determined (Budnitz et al. 2009). Sessions should occur in spring during the breeding duration and at the fall after breeding is completed.
The data from spring and fall sampling should be considered independently in analyses. More intensive trapping is necessary when sampling for absolute abundance though this should vary depending on survey objectives and choice of analysis models (Gitzen 2012). Small mammals follow multi-year cycles, and this may influence survey results.
Different environmental features should be assessed for understanding the interrelations between small mammal assemblages and their habitats in the process of trapping. Vegetation cover, structure of food availability can be recorded along trap lines. Habitat description should be done in terms of type of forests, savannah, grassland, and distance to the nearest water source, existence of rocks, termite mounds, and burrows. Microhabitats should also be recorded in standardized habitat sheets.
Some of the methods used to trap mammals include ground-based mist nets, canopy mist nets, harp traps. Since interruptions occur in some species over very large areas at 3-4 year intervals, dispersions may occur hence flooding landscape. Many challenges can be experienced if sampling small mammal populations and a number of factors can result into bias. These factors include area covered by the transect, number of traps per capture station, behavioral variation, number of capture sessions as well as survey model assumptions. Unfavorable weather may also affect capture probability and also manipulate time variation. Other mammals may also become “trap shy” after an initial capture, and this may minimize their capture probability thus interfering with the findings. Weather can also influence the behavior of a given species, which may in turn interfere with their trap ability. Trapping should be temporarily postponed during wet or unseasonably cold weather. In essence, if the traps are not strategically placed then the species may not be trapped, or this may be biased. Such techniques can be replicated in different areas to help conserve or even just reduce the mammal population. For instance in early years when rats brought plague to London,s such methods would offer amicable solutions.
In moth trapping, objective is clearly set then the survey area determined. This could entail people and articles moving from infested area. The survey area must have a suitable habitat, which are host trees and other objects to support moth population. The first category areas include affluent residential areas, cities with the military base or major universities, residential areas with high amount of relocations as well as wooded suburban residential areas. For this category, trapping density should be one trap per square miles.
Category 2 habitat for moths include areas with moderate populations such as small cities, contiguous wooded areas accessible to people as well as large, urban areas with limited habitat. The trapping density for this category is one trap per every for square miles. Category 3 areas include noncontiguous wooded areas and rural agricultural areas with widely scattered small towns. Category 4 areas include those that lack habitat and potential for introduction and none of these areas should be trapped. The final category is a category s where infestations are most likely to be artificially introduced including campgrounds, mobile home parks, sawmills and veneer mills and tourist attractions.
Light traps can be safely used in most types of habitats. The priority should be getting permission from land owners before launching the traps especially where land is protected. Health as well as safety is another area or field to be considered given that the exercise is conducted at night using light traps. Prior discussions should be held so that each member knows their role. The main challenge here may result when the team does not arrive at the trapping site early enough to identify best habitats as this may result into bias and poor results. Since light trapping is conducted at night, one may suffer an injury.
Besides, if cables are placed across the paths, someone may accidentally tamper with it, leading to errors. Field trapping occurs well on calm, cloudy nights with constant temperatures. Catches during drizzle or light rain can be so good. Moth trapping, when done at night, helps to give time to the moth to search food and reproduce as well. Sometimes trapping should be done in woodland, heath or marsh instead of exhausting the garden. Positioning of the light trap should be put correctly so as to ensure high-quality collection. Trapping from broad leaved and mixed woodland can be best done from early March through to November. Such trappings can be used by the government to help check moth population in certain places and can also be replicated where roads are constructed.
Phase 2 surveys are more detailed than phase 1. They are employed whenever detailed vegetation information is required for selected areas. NVC can also include animal information survey for and allocation of NVC type classes and provides crucial information especially on the wildlife resource based on a particular site. It also places this information in perspective of other resources likely to be found in the immediate vicinity. This information can be used when considering potential development or mitigation strategies within the area, and this method can as well be replicated elsewhere for the same purposes (Budnitz et al. 2009). For some species, only licensed individuals can conduct surveys on them though their habitat assessments can be done without anyone. For instance, newt is a protected species whose survey must adhere to this.
Different species have a particular time of the year when they can be easily found. Others are nocturnal and so their surveys must be done at night. Failure to observe such time requirements may lead to insufficient or even no data at all hence bias. Among the equipment required are satellite images. However, lack of a skilled interpreter of satellite images may lead to poor quality data which may result to bias. It is worth noting that vegetation is affected by weather condition, and this should be a crucial factor to consider in timing NVC. These phase 2 surveys can be used in areas where governments plan to implement a massive construction project, for example, construction of a stadium that may cause disruptions to many species.
List of References
Budnitz, R. J., Quinby-Hunt, M. S., & Lawrence Berkeley Laboratory, 2009, Instrumentation for environmental monitoring, Wiley, New York.
Gitzen, R. A 2012, Design and analysis of long-term ecological monitoring studies, Cambridge, Cambridge University Press.
Hill, D. A 2010, Handbook of biodiversity methods: Survey, evaluation and monitoring, Cambridge University Press, Cambridge.
