Droughts can have devastating effects on bird populations. When drought hits an area, sources of food and water for birds suddenly become much scarcer. This forces birds to make dramatic changes in their behavior in order to survive these harsh conditions. Understanding what happens to birds during droughts can help us better protect them when dry conditions occur.
What is a drought?
A drought is an extended period of abnormally dry weather that causes water shortages. Droughts are usually caused by a lack of precipitation over an extended period of time. They can last for months or even years. There are four types of drought:
- Meteorological drought – A period of abnormally dry weather.
- Agricultural drought – A period with inadequate soil moisture to support crops.
- Hydrological drought – Reductions in water resources like aquifers, lakes, and reservoirs.
- Socioeconomic drought – Water shortages that impact supply and demand of economic goods.
Droughts put considerable stress on both wildlife and humans living in the affected region. When they occur, there is not enough water to support natural habitats and human activities like agriculture and recreation.
How do droughts impact birds?
Birds are strongly impacted by droughts for several reasons:
- Lack of food sources – Droughts kill off many plants and reduce insect populations that birds rely on for food.
- Loss of nesting sites – Bushes and trees that birds nest in may die off.
- No access to water – Important bird water sources like lakes, streams, and puddles can completely dry up.
- Increased predation – With less protective cover, birds are more vulnerable to predators.
The combiniation of these factors puts severe pressure on bird populations. Food, water, and shelter all become much more limited during drought conditions.
Reduced breeding and rearing of young
One of the most dramatic impacts of drought on birds is a reduction in breeding and rearing of young. When resources are scarce, many species of birds will skip breeding or produce fewer eggs and offspring.
For example, seabirds that rely on fish may abandon their nesting colonies if food is hard to come by in surrounding waters during a drought. Songbirds nesting on dry land will have a hard time finding enough insects to adequately feed their chicks. The chicks that do hatch may be underweight and less likely to survive due to competition with siblings for limited food.
Waterfowl like ducks build nests near ponds and wetlands that can completely disappear during severe droughts. With their nesting sites gone, they are unable to breed successfully. Birds of prey like hawks and eagles need ample small rodents and animals to hunt, which also decline when drought hits the land.
Overall, the impact of drought on food and nesting resources means many birds will not attempt to breed at all. Those that do try to breed will likely have very low reproductive success and few if any young surviving to adulthood. The long-term effect is a significant decline in bird populations.
Increased risk of starvation
The lack of food resources during drought puts birds at greater risk of starvation. Their normal food sources like fruits, seeds, nectar, insects, fish and small animals become much more scarce when water is limited.
Birds can expend more energy searching farther and wider for food. But the lack of calories and nutrition can gradually lead to starvation. Smaller birds with higher metabolisms like hummingbirds are especially vulnerable when food becomes limited. But all bird species will feel the impacts of reduced food availability.
Birds that manage to find food may struggle with the lower quality options available. Breeding birds working hard to collect food for their offspring may be especially challenged by lower calorie food items. And juvenile birds dependent on their parents can starve if adult birds are unable to provide enough sustenance.
During extended droughts, the cumulative effect of food shortages adds up. Birds slowly lose weight and weaken over time without their normal level of nutrition. Starvation impacts both weak and strong birds. Without intervention, famine conditions will result in higher bird mortality rates.
Increased conflict over resources
When resources like food and nesting spots become scarce during a drought, competition between birds increases dramatically. Birds typically used to having abundant resources in their home ranges are forced to fight harder for access to the limited resources that remain.
At bird feeders and fruiting trees, aggressive species will try to claim the food sources for themselves, driving off weaker competitors. Larger stronger bird species may claim prime nesting areas, forcing smaller birds to nest in suboptimal spots or completely forego breeding. Water sources see heightened conflict too.
Birds that never interacted much in the past now find themselves fiercely competing for access to the same dwindling resources. This can manifest as aggressive behavior like fighting, squabbling, and chasing other birds away.
Some species may become territorial over areas with resources. Others may swarm sites in large numbers. Birds typically lower in the pecking order like pigeons and starlings will find themselves bullied away more often. The increased competition places added physiological stress on birds already struggling with limited food and water.
Changes in migration and movement
Species of birds that migrate or travel nomadically to find resources will be forced to alter their movement patterns during a drought. Birds that normally migrate from drier to wetter regions may have to travel farther as drought spreads across the landscape.
The loss of food and water sources in a given area may prompt earlier migration to areas with better resources. Some birds like waterfowl may delay migration or skip it altogether if their destination lacks enough water and habitat.
Resident bird species used to staying in a home territory year round may be forced to venture wider and farther than normal to find food and water. This increased movement expends extra energy for birds already lacking calories and nutrition.
Nomadic bird flocks that track resources like fruit, nectar, and insects across the landscape will have to cover far more ground to find sufficient nourishment. Birds that struggle to find enough resources in their expanded ranges face greater chances of starvation or predation.
Increased susceptibility to disease
The physical stress of surviving drought conditions also compromises birds immune systems. Lack of food, prolonged thirst, nesting issues, and increased conflict all place great strain on birds bodies.
Stressed birds in poor condition become more susceptible to bacterial, viral, and fungal diseases. Trichomonosis, avian malaria, aspergillosis, avian pox and avian flu are examples of infectious diseases birds are at higher risk of contracting during drought.
Diseases spread faster when birds congregate at limited water and food resources. Weaker birds are especially vulnerable to contagions. Loss of weight and strength during drought gives diseases a foothold to establish lethal infections.
Without intervention, sickness and disease epidemics during drought can spread rapidly and kill large numbers of birds. Even birds that were healthy before drought conditions became harsh may get sick. Drought stresses bird populations as a whole.
Vulnerability of endangered species
Bird species already endangered before a drought hits are at extremely high risk during dry conditions. Species with restricted ranges, small populations, and specialized diets suffer even more when the limited resources they depend on are affected.
For example, island species endemic to a single location have nowhere else to go if their home island becomes drought stricken. Species that need very specific habitat like forest ecosystems are vulnerable if drought kills off substantial amounts of forest vegetation.
Endangered vultures that depend on finding animal carcasses face higher risk of extinction if prey populations decline during drought. Rare hummingbirds that coevolved with unique flower species are imperiled when those partner plants die off in drought conditions.
Once endangered species numbers fall during drought, they have a far harder time recovering afterwards to restore populations. Additional pressures like habitat loss make it harder for endangered species to bounce back after drought stress. Targeted conservation efforts are necessary to prevent extinctions.
Higher predation rates
Drought conditions produce an abundance of weak, starving birds while reducing plant cover that birds depend on for shelter. This combination leaves birds much more exposed to predators like raptors, mammals, snakes, and opportunistic species.
Starving birds forced to wander widely in search of food are easy targets for predators. Loss of vegetation cover makes it harder for small birds to hide and escape attacks. Bigger more aggressive bird species may kill and eat smaller competitors when food is scarce.
Nestlings and fledglings are often the most vulnerable to drought related predation. Adults working harder to find food may frequently leave young unattended in nests. Nestlings are unable to flee predators without parental protection. Increased predator attacks can doom entire generations of young birds.
Predators themselves are challenged by limited drought resources and can also face higher mortality. But raptors and mammals better adapted for hot dry conditions have an advantage capturing prey. Drought conditions tip the outcome of predator-prey relationships in favor of predators.
Loss of species diversity
The combination of higher mortality rates along with lower reproduction means birds deaths outpace births in a region struck by drought. Areas that once supported a wide diversity of bird species will see declines in total species richness.
Specialist bird species that depend on narrow habitat niches and food sources are most likely to disappear altogether from drought zones. Even generalist adaptable species will decline without enough resources to sustain populations through multiple challenging years.
If drought persists for long periods of decade or more, local extinction of rarer species becomes likely. As species disappear over time, regions can permanently lose distinctive bird diversity that took eons to develop. Desertification exacerbates loss of ecosystem biodiversity.
Restoring vanished populations may take many bird generations or become impossible if extinct species have no outside populations to recolonize from. Careful conservation and breeding programs are needed to reestablish diverse bird communities after extended drought.
Behavioral changes
To cope with the many challenges of surviving drought, birds display behavioral shifts in activity patterns. Changes in vocalizations, social interactions, feeding, and daily rhythms help birds eke out resources until drought stresses ease.
More time spent flying and foraging replaces non-essential activities. Courtship dances and displays may get skipped or reduced to conserve energy. Vocalizations calling mates and defending territories become more sporadic.
Feeding occurs more opportunistically at whatever food sources birds can find. Migratory cues signaling seasonal movement happen earlier or alter normal migration patterns. Escape behaviors and mobbing of threats increases near limited resources.
Daily activity extends into dimmer light conditions closer to dusk and dawn. Less time is spent roosting as birds maximize daylight foraging. These behavioral shifts prioritize critical survival needs until environmental conditions improve.
Coping strategies
To overcome the threats of drought, bird species have evolved a variety of strategies to improve survival odds:
- Mobility – Being able to fly long distances to locations with better resources.
- Migration – Having the ability to predict and move to regions with abundant resources.
- Adaptability – Generalist species can utilize many habitat types and food sources.
- Food caching – Storing excess food during non-drought periods.
- Fat reserves – Storing excess calories as fat to survive temporary famine.
Species with these adaptations tend to fare better in drought conditions. However, most birds will still experience population declines and require many years of bountiful conditions to recover losses following drought.
Impacts on ecosystems
Birds perform many keystone roles in terrestrial and aquatic ecosystems. Declines in their abundance can degrade ecological health in many ways:
- Less predation of insects leading to pest outbreaks.
- Reduced scattering and germination of native plant seeds.
- Pollination drops off as pollinators decline.
- Scavengers remove less carrion allowing diseases to fester.
- Nutrient transport from sea to land plummets as seabird colonies shrink.
- Smaller prey populations after raptor and bird predation declines.
These breakdowns in food chains, plant reproduction, and nutrient movement can impact many species beyond just birds. Entire ecosystems become less resilient and face destabilization after drought’s effects on bird communities.
Long term impacts past single droughts
Even after a drought ends and conditions improve, bird populations may take years to rebound. A single severe drought can impact birds residual effects lasting years or decades afterwards:
- Starvation lowers baseline bird populations that now need to recover.
- Lost reproductive potential during drought must be made up.
- Habitats degraded by drought are slow to fully regenerate.
- Competition for scarce recovery resources limits population growth.
- It takes time to re-establish balanced age distributions and diversity.
Cycles of drought followed by temporary recovery can keep bird populations suppressed at lower equilibrium levels. This leads to an alternate stable state with reduced species variety.
Restoration of original population sizes, biodiversity, and ecosystem functions requires consistent stability and resources over long periods of time for full recovery. Climate trends leading to more frequent severe droughts make it harder for bird communities to rebound.
Providing supplemental resources
During especially severe droughts, it becomes necessary to provide supplemental food, water and shelter to help bird populations endure harsh conditions:
Food Supplements
- High energy seed mixes at multiple ground and elevated feeders
- Fruit pieces suspended in mesh bags from trees
- Nectar mixes in hummingbird feeders
- Mealworms and other live insects
- Rodent/egg protein sources for birds of prey
- Carrion for vultures/scavengers
- Fish, shellfish , or krill for seabirds
Water Sources
- Birdbaths, small ponds, or backyard pools
- Misters, drippers, or sprinklers
- Fountains and bubblers to prevent stagnation
- Rainwater catchment systems
- Open or heated pet water bowls
Shelter Options
- Nest boxes for cavity nesters
- Evergreen trees and shrubs
- Brush piles
- Artificial shade structures
- Mud for swallow nest construction
- Platforms and shelters for ground nesting
With supportive human intervention, birds resilience improves despite harsh drought environments. But conservation efforts must be sustained and widespread to offset drought impacts on broader bird communities and ecosystem health.
Conclusion
Drought presents birds with immense life threatening challenges. Food and water vanish while shelter also becomes scare. Breeding fails, disease spreads, and competition skyrockets. Populations and biodiversity decline across impacted regions. Many birds must radically change behaviors to survive. Species already endangered risk extinction without fast conservation intervention. Supplemental resources can boost survival but ecosystems need stability to fully heal. Droughts test the limits of birds abilities to adapt and persist through severe environmental changes. But providing habitat buffers and resource continuity in human modified landscapes could help bird populations endure into the future.
