Ecology surveys are an important tool used by ecologists, environmental consultants, and land managers to assess the flora, fauna, and overall ecological health of a given area. These surveys can be conducted for a variety of reasons, such as prior to new development, after restoration efforts, or simply to monitor biodiversity over time. But when is the optimal time to carry out these surveys? The answer depends on a number of factors, including the specific goals of the survey, the types of organisms being surveyed, seasonal variations, and logistical constraints. This article will explore the key considerations for determining the ideal time for ecological surveys throughout the year.
Breeding Season Surveys
One of the most common reasons for conducting an ecological survey is to search for breeding, nesting, or denning sites of specific plant and animal species. Many surveys target rare, threatened, or endangered species to locate populations and determine conservation needs. Surveys may also be done to identify conflicts between protected wildlife and proposed development. For these types of breeding season surveys, timing is critical.
Species or Group | Breeding Season |
---|---|
Amphibians | Late winter to early summer, depending on species and location. Breeding is closely tied to wetland hydrology. |
Reptiles | Spring and summer months, variable by species. |
Spring migratory birds | May and June |
Raptors | Late winter to mid-summer, depending on species. |
Bats | Late spring to summer when nursing young. |
As shown in the table above, there is significant variation in optimal breeding survey times across taxonomic groups. Within groups, timing can also vary by species and geographic location. Whenever possible, surveys should be scheduled during the peak of breeding activity when animals are most active and conspicuous. Multiple visits may be needed to accurately survey breeding activity through the season. Consultation with wildlife experts is recommended to identify ideal survey timing.
Vegetation Surveys
Vegetation surveys document the plant biodiversity within an area. This includes surveys of native and non-native plants, endangered species, and invasive weeds. While vegetation can be surveyed any time of year, the detectability of different plant species varies seasonally.
Spring surveys from May to June are ideal for observing spring ephemerals that emerge and flower before the forest canopy leafs out. Early spring surveys can also facilitate the identification of non-woody plants that die back later in the year. Summer surveys from July to August allow observation of plant reproductive structures that are key to identification, such as flowers or fruits. At this time, the forest understory is also clearer with the full leaf-out of the canopy. However, some spring ephemerals may be difficult to detect by summer. Fall surveys can target late-flowering species, but identification of plants lacking flowers or fruit can be challenging.
Ideally, conducting vegetation surveys across multiple seasons will provide the most thorough assessment of plant diversity on a site. At minimum, both spring and summer surveys are recommended. Consultation with botanical experts can help determine the optimal survey dates for target plant communities. Consideration should also be given to dates of herbarium specimen collections from the site which indicate when plants were previously documented in flower or fruit.
Avian Surveys
Bird activity follows strong seasonal patterns, presenting some challenges for effective avian surveying. Migration periods of spring and fall see the greatest diversity of bird species, but populations are transient as birds move between wintering and breeding grounds. Establishing relative abundance and nesting activity requires surveying during the breeding season when bird populations are stable within territorial ranges.
The table below outlines recommendations for common avian survey methods by season:
Survey Type | Spring Migration | Breeding Season | Fall Migration |
---|---|---|---|
Point counts | Good for diversity | Best for breeding birds | Good for diversity |
Transects | Moderate detection | Moderate detection | Moderate detection |
Area search | Lower detection | Highest detection | Lower detection |
During spring and fall migration, a combination of point counts and transects can help tally the range of migratory species moving through. For assessing resident breeding birds, area-search methods during the breeding season yield the highest detections when birds are most vocal and territorial.
Logistical Considerations
While survey timing should focus on ecological factors, logistical constraints can also play a role. Access issues are common on public lands when winter road closures are in effect. Fieldwork can also be hindered by extreme weather conditions, such as heavy rain events. And for remote field sites, the short window of snow-free access in late spring and summer may dictate survey timing.
The availability of seasonal field crews can also drive survey schedules. College students provide a field workforce during summer break, while this labor pool is lost during the school year. Scheduling around the academic calendar requires advance planning for multi-season surveys.
Funding cycles may also constrain survey timing. Multi-year surveys are optimal, but often surveys are limited to a single field season due to budgetary factors. Researchers must work within project timelines and match survey objectives to the narrow seasonal window funded.
Survey Type Considerations
Within the general time windows discussed above, survey methodology can also influence seasonal decisions. Passive survey methods, such as remote camera traps, hair snares, and sound recorders can be deployed year-round to detect elusive or nocturnal species. For mobile field methods, conditions should facilitate optimal data collection.
For example, tracking tunnels and scent stations used to survey small mammals require soft substrates. These are best placed during spring melt, after autumn rains, or when soils are otherwise moist but not frozen. Likewise, the most effective seasonal window for pitfall trapping varies regionally but focuses on periods of highest prey activity and avoidance of temperature extremes.
Habitat assessments and vegetation mapping via satellite imagery or aerial photography require leaf-off conditions. Images collected during spring leaf flush or the autumn color change provide inadequate detail on underlying habitat structure and composition. For delineation of wetland boundaries, site visits during the dry season may be needed when hydrology and soil indicators can be observed.
Additional Survey Design Considerations
Beyond the seasonal factors above, survey design should also aim to standardize additional variables that can affect detection of species. Consistency is key for valid comparisons across time and space. Variables to standardize include:
– Day length – conduct daily surveys within the same limited hours based on breeding season activity patterns
– Weather conditions – avoid precipitation, high winds, cold temperatures that reduce activity
– Time of day – survey the same locations at the same time daily/seasonally
– Tide cycles – standardize with tidal fluctuation where relevant
– Observer bias – use the same surveyors across surveys to limit bias
Conclusion
Determining optimal survey timing requires balancing a variety of factors, including species biology, seasonal activity patterns, goals of the study, and logistical constraints. While the exact survey dates will depend on the target species and location, below are some general guidelines:
– Breeding activity for most groups peaks during spring and summer months.
– Migration periods in spring and fall see high diversity fluctuations.
– Leaf-off seasons provide best habitat assessment conditions.
– Consistent timing is key for comparable data collection across sites and seasons.
– Consult wildlife experts to identify priority survey dates for species of interest.
With some advanced planning around species biology and logistics, ecologists can time their field surveys to maximize seasonal windows of opportunity. Well-timed surveys provide quality data to support science-based conservation and management decisions for ecosystems.