White Breasted Nuthatch Cardinal

Helping Nesting Birds

Nest Watch is a citizen science program offered by the Cornell Lab of Ornithology.  Like Feederwatch it depends on volunteers who agree in this case to regularly check nest boxes of certain birds to monitor and record the number of eggs in the nest and the resulting chicks. By doing this and reporting results, citizens can help scientists track status and trends in the reproductive biology of birds. There are 13 different species of common birds that can be tracked and studied.

Recently, NestWatch organized a large study of supplemental feeding of breeding Eastern Bluebirds, Black-capped Chickadees, and Carolina Chickadees and asked volunteers to participate and report their findings. The species chosen for the study are the most likely to be supplied with food and nesting cavities (boxes). The study began in 2014 and went through 2019.  In that time the scientists analyzed 24,528 nest records of these species, ranging from Alaska to Florida.

The goal of the project was to find answers to the question of how feeding wild birds impacts their reproductive

A male Eastern Bluebird ready to deliver an insect to the nest.

A male Eastern Bluebird ready to deliver an insect to the nest.

success. Eastern Bluebirds were considered supplemented if they were provided with insect larvae, such as mealworms or waxworms. For the Chickadees, supplemented food could include wild bird seeds, suet, insect larvae, or fruit.  The people participating in the study were to report when they supplemented the food;  ” was it before the eggs were laid, when the eggs were present and/or when nestlings were present”.

The resulting analysis indicated that Eastern Bluebirds who had additional food laid their eggs 6 days earlier than those who had no additional food. The supplemental feeding didn’t have any impact on the Chickadees egg laying. The advantage for bluebirds who lay eggs earlier might allow them to produce another clutch later in the season. There is also a risk associated with laying eggs earlier in that they have a higher chance of being hit with deadly cold fronts in early spring.

Clutch size did not change for either species, except for a small increase in clutch size for later in the season. Access to extra food at that time may have been the reason for the slight increase. Chickadees rarely lay a second clutch.

This nest box used by Black-capped Chickadees has a predator guard at the entry hole.

This nest box used by Black-capped Chickadees has a predator guard at the entry hole.

Another factor in the study was the presence or absence of predator guards. These are additional structures or devices that attach to the entrance hole making it difficult for predators (like cats or raccoons and some birds) to be able to reach into the nest box.  Predator guards are associated with increased nest survival. A bluebird nest box with a predator guard and additional food showed nest survival improved by about 5%.

The study results also suggest that additional feeding may be helpful for nestlings to make it through the earlier part of the breeding season when they are vulnerable to cool weather.

The Black-capped and Carolina Chickadees did not have higher nest survival when supplemental food was available. Another study found that Eastern Bluebird nestlings provided with additional food were 5.2% heavier as they approached fledging age. Research has shown that relatively heavy fledgling have a better likelihood of surviving their first year than nestlings of lighter weight. Black-capped Chickadees, once again, did not benefit even though they were provided live mealworms at nest boxes.

The researcher did not expect the results that showed so much difference between the bluebirds and chickadees. It is true that Eastern Bluebirds have a more limited diet; basically insects and fruit. Both species of Chickadees have a broader diet and therefore may not be as sensitive to food shortages during the breeding season. Even if they didn’t show the same results as the bluebird’s, surplus food may help them in the nonbreeding season.

A male Eastern Bluebird prepares to feed a mealworm to a fledgling.

A male Eastern Bluebird prepares to feed a mealworm to a fledgling.

Providing bluebirds with insect larvae may not be common, but it is growing in popularity among those who are especially intent on seeing the bluebird population increase.

Even though the breeding season is over for this year it is good to know more about our impact of feeding birds. In the U.S. as of 2018 there were more than 59 million people engaged in this hobby. Keep up the good work.

By Kate Crowley