Sand perch covers are protective covers that can be placed over exposed sandy areas to provide shelter and shade for ground-dwelling birds. They are often advocated as a tool for enhancing habitat for threatened shorebird species that rely on open sandy habitats for nesting and roosting. However, the effectiveness of sand perch covers for birds remains debated among ornithologists and conservationists. In this article, we will examine the potential benefits and drawbacks of sand perch covers for birds and evaluate whether they are an effective habitat management strategy.
What are sand perch covers?
Sand perch covers, also known as shelter covers or nest shelters, are structures made from natural or artificial materials that are installed over areas of open sand. They are designed to provide shade, shelter from weather and predators, and visual isolation. Sand perch covers are commonly constructed from wood slats, brush piles, or mats made from coconut fiber or synthetic materials. They are elevated slightly off the ground and include openings on the sides to allow entry and exit for birds. The covers diffuse direct sunlight and help regulate temperature over sandy areas used by ground-nesting shorebirds.
Why are they used?
Sand perch covers aim to improve habitat quality for threatened shorebirds that rely on sparsely vegetated sandy habitats. Shorebirds such as plovers, terns, and skimmers frequently nest in open, exposed areas on beaches, sand flats, and shorelines. However, human disturbance, predators, extreme weather, and vegetation encroachment can degrade the suitability of these habitats. Sand perch covers attempt to mitigate these threats by providing sheltered nesting and roosting microsites. They are often installed proactively at key shorebird nesting areas or reactively after declines in nesting shorebirds are observed. When thoughtfully implemented, sand perch covers may support shorebird populations of conservation concern.
Potential benefits of sand perch covers
1. Provide shelter from predators
One of the main intended benefits of sand perch covers is reducing predation on ground-nesting birds and their eggs and chicks. By providing a sheltered nest site, sand perch covers may help conceal nests from visual predators like gulls, crows, mammals, and other birds. The cover and partial enclosure offers protection for incubating adults, eggs, and flightless chicks that are extremely vulnerable to predation in open beach habitats. Even if predators enter the cover, birds may be better able to escape or distract predators when under cover. Research on plover nesting success has found higher survival rates for nests under shelters versus exposed nests.
2. Reduce human disturbance
Sand perch covers may minimize disturbance from human recreation, research, management activities, and development. Shorebirds attempting to nest and roost on public beaches and multi-use areas are subject to high levels of human activity that can lead birds to abandon nests. Perch covers can provide a buffer from human approach and motion. By delineating sensitive nesting areas, covers also serve as visual cues to help people avoid nests during the breeding season. Signage is often paired with perch covers to further designate the area as protected habitat.
3. Moderate microclimate
In hot environments, sand perch covers create shade and ventilation that can prevent overheating of eggs and chicks. The structures lower sand surface temperature, reducing exposure to extreme heat that can kill embryos or cause developmental issues. In areas with cool, windy, or frequently overcast conditions, the covers conversely retain warmth and protect from chilling. Perch covers act as windbreaks and help maintain favorable microclimate conditions for incubating birds and their offspring.
4. Extend usable nesting habitat
In areas where vegetation growth or anthropogenic development has reduced open sandy habitat, sand perch covers may expand the limited suitable nesting grounds available to beach-nesting species. By providing artificial nesting patches amid suboptimal surroundings, the total habitat area able to support nesting is increased. If natural nesting grounds are completely eliminated in a region, sand perch covers may even allow introduction or restoration of shorebird nesting where it no longer occurs.
| Potential Benefit | How It Helps Birds |
|---|---|
| Shelter from predators | Conceals and protects nests, adults, eggs, and chicks from visual predators |
| Reduce human disturbance | Creates a buffer from recreational activity and delineates sensitive nesting habitat |
| Moderate microclimate | Reduces temperature extremes and wind exposure for nests |
| Extend usable nesting habitat | Provides artificial nesting sites in degraded or restricted habitats |
Potential drawbacks of sand perch covers
1. May attract certain predators
While perch covers help conceal nests from aerial and surface predators that locate prey visually, they can simultaneously attract other predators that focus on scent or shelter. Mammalian predators like foxes, coyotes, raccoons, and skunks may be drawn to covers if they provide hiding places, shade, or trap scents. avian predators including gull species are highly attracted to structure and may colonize covers. Continued predator monitoring and adaptative management is important to ensure covers do not increase predation risk from certain species.
2. Alter natural substrate conditions
Adding structures and shade alters the natural temperature, moisture, and substrate consistency in the habitat. Some research indicates that soil moisture and humidity is higher under sand perch covers, which can impact suitability for eggs and chicks that rely on well-drained, aerated sand for development. The structures can also degrade over time and deposit materials into the sand that change its natural composition. Shorebirds exhibit strong nest site fidelity and may abandon areas if habitat conditions are altered.
3. Encourage competing native species
While sand perch covers aim to enhance habitat for specific species of concern, they may simultaneously benefit predator or competitor species that also prefer sheltered nesting areas. Wrens, snakes, and burrowing owls readily inhabit artificial structures and compete with shorebirds for nest sites and resources. Native species should be monitored and controlled if they begin displacing the target species in habitat enhanced with covers.
4. Require maintenance and monitoring
Sand perch covers have relatively short lifespan, particularly those made with natural vegetative materials. Covers require ongoing maintenance, repairs, and replacement that increase management costs over time. They must be consistently monitored to check for degradation, predator occupation, competing species, and effectiveness for the target species. Long-term resources and commitment are needed for cover installations to meet conservation goals.
| Potential Drawback | How It May Harm Birds |
|---|---|
| May attract certain predators | Covers could shelter or attract mammalian predators and opportunistic bird predators |
| Alter natural substrate | Changes to moisture, temperature, and sand composition under covers may degrade habitat quality |
| Encourage competing natives | Species that also use shelters like wrens and burrowing owls may displace rare shorebirds |
| Require maintenance and monitoring | Covers degrade over time and need commitment to replacement and oversight |
Key considerations for effectiveness
Site selection
For maximum benefit to target species, covers should be selectively located in areas with highest need. Installing covers in suboptimal habitat lacking recent evidence of nesting activity may provide little boost. Covers are best targeted to zones with high historical nesting that have declined due to identifiable threats that covers can ameliorate. Ongoing monitoring informs strategic placement and density of covers over time.
Cover density
Clustering too many covers together can facilitate predator movement between structures or create overly damp or cool conditions. But covers that are too sparse fail to provide adequate sheltered nest sites within a territory. Appropriate cover density depends on the target species, site characteristics, and preexisting cover. Adaptive management allows adjusting density based on monitoring data.
Cover maintenance
Maintenance increases longevity and functionality of covers. Degraded covers should be repaired or replaced promptly. Built-up predator scent, substrate changes, and excessive shading can be mitigated by rotating or airing out covers between breeding seasons. Vegetation growth around covers should be controlled to maintain open surroundings.
Predator management
Proactively minimizing predators, particularly those attracted to structures, improves cover effectiveness. Predator exclosures around cover clusters may be useful. Lethal control is controversial but most impactful where key avian or mammalian predators are identified through monitoring. Non-lethal deterrents such as wires, harassment, or relocation are lower impact alternatives.
Public education
Education programs improve public compliance with cover restrictions and reduce disturbance in protected areas. Signage, volunteer steward programs, and outreach help convey that human activity near covers threatens vulnerable wildlife. When the public understands the conservation purpose, they become partners in success.
Evidence for impacts on birds
Research on shorebirds has shown mixed effects of sand perch covers on factors like nest density, nest success, and chick survival. Findings vary across study locations, cover materials, implementation strategies, and target species. Some key patterns in published studies include:
| Study Location and Target Species | Main Findings |
|---|---|
| Piping plover in Ontario, Canada | Higher nest success but lower chick survival under wire mesh shelters vs. unsheltered nests |
| Piping plover in Missouri River, USA | No difference in nest or chick survival between sheltered and open nests |
| Snowy plover in Florida, USA | Higher nest success but lower chick survival under coir mat shelters |
| Least tern in New York, USA | No difference in nest density or nest success with wood or fabric covers |
These mixed results illustrate that sand perch covers are not universally beneficial or harmful across settings and species. More experimental research into optimal design, placement, density, maintenance, and pairing with predator control is needed. Long-term monitoring of cover impacts on both target and non-target species provides critical data to refine strategies.
Key evidence gaps
– Post-fledging survival and recruitment with shelters vs. open nesting
– Fitness consequences of altered microclimate under shelters
– Effectiveness of alternative cover materials and configurations
– Cost-benefit analysis of covers vs. other management options
– Testing of stewardship, signage, and deterrent techniques as complements to covers
Conclusion
Sand perch covers show promise for enhancing threatened shorebird habitat in certain contexts, but also have potential downsides to consider. Overall, the existing research indicates they are not a universally appropriate or effective management strategy. Covers likely need to be tailored to specific sites and supplemented with other measures like public engagement, predator control, and habitat maintenance for maximal benefit. More experimental research can help refine best practices for cover installation and maintenance. When thoughtfully implemented and monitored, sand perch covers may aid conservation of beach-nesting birds disrupted by human activity, predators, and habitat loss. But they should be just one component of integrated habitat management rather than a panacea. Their costs and benefits compared to alternative strategies must be weighed. With careful evidence-based application, sand perch covers can contribute to protecting imperiled shorebird populations at key breeding sites.
