Vigilance is the Key in a One-Pair “Colony”; 25 Ways a Single Nesting Pair Can Fail

Ken Kostka
American Swallow Conservancy
Pittsburgh, PA

The most difficult part of establishing a martin colony is attracting the first breeding pair. Some people try for years, even decades, to attract that first key pair. If they breed successfully, that success usually translates into the beginning of a martin colony, with multiple breeding pairs the following season. But if that first pair fails to fledge at least one nestling for any reason, years of effort are thwarted. In 1999, I attracted one pair of martins to my parent’s residence near Pittsburgh. The nestlings died of blowfly infestation before they were a week old, and it was 12 years before another pair attempted to nest in the immediate area. In 2011, I attracted another nesting pair to a site 700 feet away. (I had purchased my own house just up the street.) I was on pins and needles since I knew that my 30 year effort to establish a colony in Natrona Heights depended on this pair’s breeding success. I knew that vigilance during that first breeding season would be the key. While there can be events beyond a person’s control, an aggressively vigilant landlord is much more likely to avoid various events that could result in breeding failure. I have listed all the reasons I could think of that can cause a nesting pair to fail. Most are preventable; some are not. Some are partially preventable. I have provided links to pages with more information about some potential threats. The bottom line: keep the parents and nestlings alive and healthy.

House Sparrows depredation House Sparrows can harass adults, break eggs, and kill small nestlings. To prevent: House Sparrows can be eliminated by trapping or shooting. Trapping is by far the most effective control method, and trapped sparrows can be used to lure more sparrows. Shooting is also effective, but I prefer to avoid the possibility of spooking the martins, especially early in the season before they are committed to the site. Nest removal is sometimes used as a control method but is often ineffective and House Sparrows can “retaliate” by destroying martin eggs.

Black Rat Snakes can climb both wooden AND METAL poles to eat adults, nestlings, or eggs. To Prevent: install climbing predator guard(s) on pole. Common mistakes: 1) not putting guard high enough above winch, allowing snake to use winch to maneuver around guard 2) leaving cracks bigger than 1/8th inch between the pole and the guard, allowing snakes to squeeze through. DO NOT underestimate the ability of rat snakes; I once had one get past TWO pole guards and eat a family of martins.

Nest parasites. Parasites that breed in the nesting material, especially blowfly, can weaken and even kill nestlings. Do NOT wait until the nestlings are 10 days old to check the nest as blowfly can become a problem in as little as 2-3 days after Sierra Exif JPEGhatching. I lost an entire clutch to blowfly parasitism in 1999, when the nestlings were less than a week old. Nest parasites can be eliminated by full or partial nest replacement. Nesting cavities can be treated with Sevin early in the season to prevent mites.

Starling depredation.  European Starlings, another invasive and unprotected species, can harass, injure, and kill adult martins and nestlings, as well as destroy their eggs. To prevent: exclude starlings from nesting cavities with starling-proof entrance holes. However, they can still lurk on porches and attack martins. I had a starling chase my alpha female off of her porch and take her to the ground. To prevent harassment by starlings, trap or shoot them in the vicinity of the martin housing. Trapping is preferred since it is more quiet.

Cold/rainy weather   Extremely poor weather lasting more than three consecutive days can starve adults and nestlings, or cause adults to abandon their eggs. Martins can be trained to accept crickets tossed into the air. Be prepared to use this emergency feeding technique if this occurs.

Extreme heat   Very high temperatures (high nineties or above) could cause the death of nestlings in poorly insulated or poorly ventilated housing. Insure there is adequate air flow by drilling ventilation holes near the top of the cavity. Train a mister on the housing to cool it down

Great Horned Owls   can kill adults or nestlings by landing on the housing at night and either reaching into the compartments or scratching/flapping on the entrance hole area in an attempt to flush the martins out. Lighting the housing, playing a radio, and positioning a scarecrow or mannequin will help to prevent owl incursions, but nothing beats being there in person to chase owls away. Prior to receiving federal protection, landlords often killed owls by shooting or pole-trapping.

“Hawks”  (mainly accipiters – usually Coopers Hawks) will hunt adults and fledglings. To reduce their chances of success in killing your martins, keep the martin housing as far as possible from trees and other structures. Hawks use nearby trees to hide their flight approach when ambushing martins. Simply being present at your colony to discourage hawk attacks is a great strategy.

Raccoons   Raccoons will climb poles at night, reach into cavities, and eat martins. Raccoons CAN climb metal poles! To Prevent: install climbing predator guard on pole. Common mistakes: installing an inferior guard, not putting guard high enough above winch (which allows raccoon to use winch to maneuver around guard). Chewed off martin wings on the ground near the pole or on the roof of the housing are tell-tale signs of raccoon predation.

Winch or cable failure   If the winch fails or the cable breaks and the house freefalls, the eggs will break or small nestlings will possibly die, causing the parents to abandon the site. Keep winches and cables oiled and in good repair.

Poisoning.   If a martin eats an insect that had been sprayed, they could become sick and die. I was spraying carpenter bees that were eating holes in my shed when I realized that if one of the half-poisoned bees flew off and was eaten by a martin, that could be the end! Also, do not let eggshell or oystershell stay wet. It could start breeding bacteria that could harm martins. Do not let ponds stagnate. Do not allow emergency feeding supplies like scrambled egg or crickets to become old and moldy.

Injury.  One parent’s death could mean reproductive failure. Wing or leg entrapment could cause such a death. Wing entrapment sometimes occurs while martins are fighting, causing a martin to get stuck in the entrance hole.. Visually monitor all entrance holes with binoculars, especially early in the season when martins are fighting over cavities. Legs can also get stuck in cracks of housing or feeders. Seal all cracks, especially near porches and perches, as well as on feeders.

Female scared off young nestlings at night   When nestlings are less than about 10 days old, they cannot maintain their own body heat and must be brooded by the female at night to keep from becoming hypothermic. Therefore, if anything scares the female off of the nest at night, the eggs or nestlings can perish. Examples of things that can scare a female off of a nest at night include owls scratching at the entrance hole, the pole or house being hit or shaken by vandals, or someone lowering the housing. I considered fencing off a small area around my house when I had only one nesting pair to prevent neighborhood kids from accidentally running into the pole if horsing around in my backyard after dark. Keeping a spotlight aimed at the base of the housing would also prevent someone from accidentally running into it at night and discourage vandals.

Human Error.   Landlord blunders include mistakes like dropping the nest tray and breaking the eggs while conducting a nest check or losing hold of the winch handle while raising/lowering the house, causing it to freefall and break the eggs. But do not be discouraged from doing nest checks, The disruption will not cause your martins to abandon the site. Conduct nest checks only in the early afternoon and only on good-weather days. Pay attention to what you are doing when attending to the housing; do not talk to other people that might distract you or make loud noises. Make a short list of things you need to do – in the order you need to do them. Nest checks require a certain amount of courage; it is easier to cower in fear that you may do something wrong or scare your martins away. Nest checks are especially important around hatching time, when egg-capping can prevent an unhatched egg from hatching. This occurs when one half of an already hatched eggshell gets stuck on one-half of an unhatched egg, keeping it from hatching. Just remove the hatched eggshell. Also, nest parasites can become abundant and kill nestlings when they are less than a week old, so don’t assume you won’t have to deal with parasites until the nestlings are 10 days old.

Extreme wind gusts and other wind events like tornadoes or microbursts can destroy nests by destroying the housing. Lower the housing when severe storms with strong wind gusts are imminent – but only during the day. NEVER lower the housing at night or if the martins have already entered for the night. Make the housing less wind-resistant by removing gourds that are not being used (after there is no longer a chance of new nestings.)

Vandalism Children or adults can shoot or throw stones at the martins, as well as shake the pole and lower the house to vandalize it. Monitor the housing closely.

Cats  Cats or dogs can kill parents while on the ground fighting or gathering nest material. To prevent: provide nest material on an elevated platform. Keeps cats and dogs out of the yard or fence off an area under the housing

Wasps  There is a species of exotic wasp that has become very common. It nests in
bird housing and is very aggressive, often causing cavity nesters like bluebirds or chickadees to abandon their nest. Do frequent (every 2 days) checks of the housing to make sure wasps aren’t becoming established. You can put a thin film of petroleum jelly on the ceilings of cavities and gourds to keep wasps from building.

Crows & Gulls  Each can act as aerial predators and cause nesting failure by snatching young out of the entrance hole. Owl guards will usually foil these attempts.

Bluejays and Grackles  Rarely, these two “predatory songbirds” can enter nesting cavities and kill nestlings. Both can be denied entry by using Starling-proof entrance holes.

Wrens  Wrens can break martin eggs. Keep martin housing as far as possible from vegetation and do not allow wrens to nest on your property. By no means allow them to snoop around your martin housing when eggs are present.

Squirrels   can climb poles and eat eggs or small nestlings. Install a climbing animal guard and keep housing away from trees.

Hailstorm.  Large hail can kill or injure adults and break natural gourds.

Lightning.  Direct lightning strikes can kill adults or destroy eggs. Ground your houses!

Sickness  One parent could always die of an undetermined ailment. This is unpreventable. However, martins in colonies that are trained to take supplemental feedings tend to be healthier and better able to withstand stressful events like bad weather or injury.

General Tips: Monitor. Monitor. Monitor.  Keeping your eyes on the housing as often as possible is a great way to help insure a successful breeding attempt. I kept a spotlight aimed at the housing at night all season long and made it a habit to look outside and walk around at night as often as possible. Consider fencing off a small area under your housing to keep out kids, cats, and any other threat. Play a radio at night. Be present in your yard so the martins become accustomed to your presence.
Having a “backup nest” is also a good strategy. This would be a nesting attempt at an established colony that is on approximately the same timetable as your own. If something were to happen to the eggs or nestlings, you could quickly substitute eggs or nestlings of approximately the same age and thus keep the parents from abandoning. Please note that this is technically illegal, and would require permits.

Multiple Structures. After you have attracted multiple breeding pairs, I recommend having at least two housing structures on separate poles. For example, TWO T-14’s or TWO gourd racks or one of each. This prevents a catastrophe (like a winch failure, predator incursion, or windstorm) that might affect one house from wiping out your whole hard-earned colony. Another way to think of it is not having all your eggs in one basket!

While all of this may seem extreme, do not fear! This hyper-vigilance is only necessary for the first year. In subsequent years, after you have attracted multiple breeding pairs you can let your guard down a little.


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