TREE SWALLOW NEST BO X PROJECT 2022 Summary Report Ilya Povalyaev , BSc, RPBio & Melissa Hafting , BSc City of Richmond Photo: Melissa Hafting 2 GLOSSARY Clutch The number of eggs laid by one bird during one nesting season. Fledge To leave the nest once flight capable. Occupancy Rate The proportion of nest boxes that were used for nesting. Nesting Success Rate The proportion of eggs that hatched and ultimately fledged. Background In 2021, the City of Richmond and Melissa Hafting initiated a Tree Swallow Nest Box Project at three parks: Garden City Lands, Garden City Park , and Terra Nova Natural A rea The objective of the project was to provide additional nest sites for Tree Swallows because they are declining and suitable natural nesting cavities are limited in these parks The year 2022 represented the second year of monitoring for the City of Richmond Tree Swallow nest box program. Nest boxes were checked on May 23 - 24, June 26, and August 7 and 9 at which point they were cleaned at the end of the nesting season. Data was entered into Project Nestwatch for Birds Canada. This report summarizes mo nitoring results and provides recommendations to improve program outcomes. Tree Swallow Nesting Ecology Each spring, Tree Swallows arrive in Greater Vancouver in late February or March. 1 Male tree swallows usually arrive and defend a nest cavity up to several days prior to female arrival. 2 Pairing begins as soon as females arrive on the breeding grounds. Pairs deposit a few pieces of nesting material in the nest cavity shortly after pair formation, but actual nest construction begins several weeks later and is completed almost entirely by f emales. 2 Nests are constructed from grasses and extensively lined with feathers of other species. 2 Egg laying typically occurs throughout May and June, but can begin as early as mid April. 1 Clutch size is usually 4 to 6 eggs, with one egg laid per day. 1 ,2 Typically only females incubate the eggs, starting on the day the penultimate egg is laid and lasting for 14 to 16 days. 1,2 The male does not feed the incubating female. The female incubates in bouts of 11 to 15 minutes, followed by 7 to 9 minutes off t he nest. 2 Second broods have been assumed to be very rare in northern portions of range and is usually associated with replacement clutches after the failure of the first clutch. 2 Following hatching, nestlings have poor thermoregulation during their first 7 to 8 days of life and require frequent brooding by the female to maintain body temperature. 2 Parents begin feeding nestlings as soon as they hatch and continue until nest departure. Parents carry food in their bill and place it directly into the open mo uth of a begging nestling. During periods of peak nestling demand, parents may feed as many as 6,000 to 7,000 insects in a single day. 2 Nestlings usually depart from the nest 15 to 25 days after hatching. 1 Young can fly when they leave the nest for the fir st time and generally do not return to the nest once they have flown. 3 Garden City Park Tree swallows nested in one (box #3) of the three nest boxes at Garden City Park in 2022 (Figure 1) . The clutch size of this nest was not determined because it was still incomplete when checked on May 23 (only two eggs present), but some of the young had already fledged by th e next check on June 26. The entire clutch successfully fledged as no unhatched eggs or dead young were present in the box on August 9. Tree Swallow occupancy rate at Garden City Park was 33% and nesting success was 100%. Additionally, Black - capped Chickad ee s fledged six young from box #1. Figure 1 : Next box locations at Garden City Park. Yellow placemarks indicate locations of nest boxes occupied by Tree Swallows, green placem ark s indicate s the locations of nest boxes occupied by Black - capped Chickadees, and white placemarks indicate locations of unoccupied nest boxes. Numbers next to the placemarks correspond to the nest box number. 4 Garden City Lands Swallows nested in 18 of the 20 nest boxes at Garden City Lands in 2022. Seventeen boxes were used by Tree Swallows and one box (#5) was used by Violet - green Swallows (Figure 2) . Occupancy rate more than tripled compared to 2021 when only five boxes were used. Adult tree swallows were observe d entering box #16, however its contents could not be checked because it was installed in the middle of the pond and was not accessible. Therefore, the number of eggs and fledged young is unknown and this box is excluded from the statistics presented herei n. Two clutches were laid in box #18, but it is unknown whether they belonged to the same adult pair or different pairs. The first clutch successfully fledged six young, but the second clutch of five nestlings and the adult female were found dead inside th e box on August 7. Excluding box #16 due to unknown clutch size and outcome, a minimum of 88 Tree Swallow eggs were laid, with an average clutch size of 5.18 eggs/nest. Six eggs from three boxes did not hatch. In total, 69 young fledged, resulting in a nes ting success rate of 78.4%. Dead nestlings were recorded at three boxes, totaling 13 individuals. Box #20 and box #18 lost complete clutches. The nesting success rate in 2022 was lower than in 2021 (91.3%), but the number of young fledged in 2022 (n=69) wa s substantially greater than in 2021 (n=21) due to the higher occupancy rate. Meanwhile, Violet - green Swallows in box #5 successfully fledged their entire clutch of 5 young (Figure 3). Figure 2 : Next box locations at Garden City Lands . Yellow placemarks indicate locations of nest boxes occupied by Tree Swallows, purple placemark s indicate s the locations of nest boxes occupied by Violet - green Swallows, and white placemarks indicate locations of unoccupied nest boxes. Numbers next to the placemarks correspond to the nest box number. Figure 3 : Female Violet - green Swallow exiting box #5. 5 Terra Nova Natural Area Tree Swallows used 14 of the 18 next boxes installed at Terra Nova Natural Area in 2022 (Figure 4). This was a substantial increase from 2021 when 8 box es were used. The clutch size for one box (#14) is unknown because it did not contain any eggs during the first check on May 23, and by June 26 only one nestling was present with the others assumed to have fledged. A total of 69 eggs were documented, with an average clutch size of 5.23 eggs/nest if box #14 is excluded from the calculation. There were only three eggs in box #10 that did not hatch. In total, 42 young fledged from nest boxes at Terra Nova, resulting in a nesting success of 60.9%. Dead nestlings were recorded at 10 boxes, totaling 24 individuals. While most boxes lost 1 to 2 nestlings, the entire brood (6 nestlings) perished at box #10, meanwhile boxes #2, #3, and #13 lost more than half their brood. The nesting success rate in 2022 (60 .9%) was lower than in 2021 (77.5%), however the total number of young fledged was greater in 2022 (n=42) than in 2021 (n=31) due to the higher occupancy rate. In addition to Tree Swallows, Black - capped Chickadees successfully nested at box #5. An unkno wn bird, likely a Northern Flicker, attempted to excavate and enlarge the entrance hole at four next boxes: #10, #11, #12, and #13. Damage to three of these boxes was minor and two of them (#10 and #13) were subsequently used by Tree Swallows. However, box #12 sustained considerable damage and the front panel needs to be replaced. Figure 4 : Next box locations at Terra Nova Natural Area pond (top) and field (bottom) . Yellow placemarks indicate locations of nest boxes occupied by Tree Swallows, green placemarks indicate locations of nest boxes occupied by Black - capped Chickadees, and white placemarks indicate locat ions of unoccupied nest boxes. Numbers next to the placemarks correspond to the nest box number. 6 Summary Tree Swallows continued to nest at all three parks where the City of Richmond installed nest boxes: Garden City Park, Garden City Lands, and Terra Nova Natural Area. Metrics for each park are presented in Table 1. Three notable trends from 2022 are described below. 1. The number of nest boxes used b y Tree Swallows increased substantially in 2022 Nest box occupancy rate more than doubled in 2022, with 32 of 42 (76.2%) nest boxes used by Tree Swallows. Occupancy rate was highest at Garden City Lands, surpassing Terra Nova Natural Area from 2021. 2. The number of fledged young increased A total of 115 Tree Swallows are estimated to have fledged in 2022, representing an increase from an estimated 54 fledged young in 2021. The increased productivity is the outcome of an increased occupancy rate. Table 1 : Summary of Tree Swallow Nesting Success in 2022 and 2021. Year Location Number of Nest Boxes Number of Nest Boxes Used Occupancy Rate (%) Number of Eggs Number of Young Fledged Success Rate (%) 2022 GCP 3 1 33.3 4* 4* 100.0 GCL 20 17 85.0 88 69 78.4 TN 19 14 73.7 69 42 60.9 Total 4 2 32 76.2 1 6 1 115 71.4 2021 GCP 3 1 33.3 4 2 50.0 GCL 20 5 25.0 23 21 91.3 TN 19 8 42.1 40 31 77.5 Total 42 14 33.3 6 7 5 4 80 .6 GCP = Garden City Park; GCL = Garden City Lands; TN = Terra Nova Natural Area. * Number of eggs is unknown. An estimate is provided based on 2021 clutch size at this box. The entire clutch successfully fledged. Tree Swallow nest with eggs. Nests are constructed from grasses and lined with loose feathers coll ected from other species. Adult female Tree Swallow incubating eggs. Tree Swallow nestlings >12 days old. 7 3. T he proportion of Tree Swallow nestling mortalities increased , likely due to high temperature extremes during the nesting season. In total, 37 dead nestlings were documented, resulting in a nesting success rate of 71.4% (measured as the proportion of eggs that resulted in fledged young). This represents a decrease from 2021 when nesting success rate was 80.6%. An alternate way of expressing nesting success is that the average number of fledged young per occupied nest box was 3.48 in 2022, and 3.86 in 2021. Terra Nova Natural Area had the highest losses, however complete clutches were als o lost at two boxes at Garden City Lands (boxes #18, #20) along with a partial clutch at a third box. In addition, the adult female also died in box #18. The cause of these mortalities is uncertain but it is suspected that most mortalities were the result of air temperature extremes, since developing nestlings have limited ability to regulate body temperate. Tree swallows breeding during periods of nighttime nest box temperatures <17.5 ° C or daytime nestbox temperatures >35 ° C have been reported to be less l ikely to fledge offspring. 3 Historical data from the weather station at the Richmond Nature Park indicates daily maximum temperatures approached 30 ° C in late June (e.g., 28.0 ° C to 32.0 ° C from June 25 to 27) and intermittently throughout July (e.g., 28.0 ° C to 28.5 ° C on July 11 to 12; 31.5 ° C on July 26). 4 The air temperature inside the nest boxes is expected to be higher than the outside air temperature due to limited air flow, although the degree magnitude of the difference is unknown. It is suspected that maximum air temperature in the nest boxes exceeded the optimal range (i.e., >35 ° C) for tree swallow fledging success during the 2022 nesting season. Figure 5 : Tree Swallow mortalities likely due to high temperature extremes during the nesting season. Left: Nestlings in nest. Right, top: Dead adult female (note completely dark bill and fully developed primaries [wing fea thers] indicating it is an adult. Right, bottom: Dead nestling (note yellowish bill base and short, not fully grown primaries [wing feathers] indicating it is a nestling). 8 Recommendations The following recommendations are provided to reduce the risk of nestling mortality due to heat: § Add heat shields. Heat shields consist of a thin piece of plywood mounted to the top and sides of the nest box on spacers that are ½ to ¾ inch long. An example heat shield plan from the Texas Bluebird Society 5 is provided in Appendix A. A deviation from this plan is that a front shield is not r ecommended for Tree Swallow boxes such that it does not interfere with adult swallows entering, leaving, or perching on the box (Appenidx A, Photo 1). § Paint the exterior surface of nest boxes white. Experiments have shown that white nest boxes experience lower temperatures because they have greater surface reflectance and absorb less solar radiation 6, 7 § Add ventilation holes. Ventilation holes should be 1/8 inch to 1/4 inch in diameter and should be drilled into the sides of the nes t box just a bit belo w the roofline to allow air flow. A vent blocker should be in stalled that can close the ventilation holes during cool or wet weather (e.g., early spring) and opened during heat waves to allow nest box cooling. A vent blocker can be made from a thin piece of wood that pivots on a screw (Figure 7). The vent blocker must be thin enough that it can slide freely below the heat shield when in the open position. If ventilation holes are added, drain holes in the nest box floor are also necessary to allow any water that is let in to drain. One drain hole with a 1/8 inch diameter should be added to each corner. A fine mesh screen should be stapled to the inside of the box over the ventilation and drain holes to prevent insect infestation while allowing airflow. F igure 8 : Ventilation hole with vent blocker closed (left) and open (right). Photo: www.treeswallows.com. 9 The following recommendations are provided to prevent flickers from damaging nest boxes by excavating and enlarging the entrance hole. § Install “sandwich holes” on the front panels of the nest boxes at Terra Nova Natural Area that sustained damage from northern flickers (i.e., boxes #10, # 11, #12, and #13; Figure 6). Sandwich holes consist of a thin steel plate with a 1 - 3/8 inch hole, attached to a cedar strip with a 1 - 3/8 inch hole, and the holes aligned (Figure 7 ). This piece is then screwed on to the existing nest box with the steel plat e facing in such that the steel plate is sandwiched between two wooden pieces. F igure 7 : Sandwich hole to prevent flicker damage to nest box entrance holes. Inside facing left. Photo: Peter Ward. F igure 6 : Northern Flicker damage to nest box entrance hole at Terra Nova Natural Area. 10 References [1] Campbell RW, Dawe NK, McTaggart - Cowan I, Cooper JM, Kaiser GW, McNall MCE, Smith GEJ. 1997. The Birds of British Columbia. Volume 3: Passerines – Flycatchers through Vireos. University of British Columbia Press, Vancouver, BC, Canada. [2] Winkler DW, Hallinger KK, Ardia DR, Robertson RJ, Stutchbury BJ, Cohen RR. 2020. Tree Swallow ( Tachy cineta bicolor ), version 1.0. In: Birds of the World (Poole AF, editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.treswa.01 [3] Ardia, DR. 2013. The effects of nestbox thermal environment on fledging success and haematocrit in Tree Swallows. Avian Biology Research, 6(2):99 - 103. [4] Government of Canada. 2022. Daily Data Report for July 2022, Vancouver International Airport Weather Station. Available at: https://climate.weather.gc.ca/climate_data/daily_data_e.html?timeframe=2& Year=2022&Month=7&Day=20&hlyRange =%7C&dlyRange=1977 - 03 - 01%7C2022 - 07 - 28&mlyRange=1977 - 01 - 01%7C2007 - 02 - 01&StationID=837&Prov=BC&urlExtension=_e.html&searchType=stnName&optLimit=yearRange&StartYear=1840&EndY ear=2022&selRowPerPage=25&Line=0&searchMethod=contai ns&txtStationName=richmond+nature+park . Accessed: 21 August 2022. [5] Texas Bluebird Society. 2014. Heat Shield Plan. Available at: https://homepage2.texasbluebirdso ciety.org/documents/heatshield_plans.pdf . Accessed: 21 August 2022. [6] Griffiths SR, Rowland JA, Briscoe NJ, Lentini PE, Handasyde KA, Lumsden LF, Robert KA. 2017. Surface reflectance drives nest box temperature profiles and thermal suitability for targe t wildlife. PLoS ONE, 12(5):e0176951. https://doi.org/10.1371/journal.pone.0176951 [6] Horacek CG, Stumpf K, Powell W. 2022 Effect of Nest Box Temperature Mitigation Treatments on Nest Success and Nestling Condition in a Southeastern Population of Eastern Bluebirds ( Sialis sialis ) Graduate Research Posters. 42 Available at: https://kb.gcsu.edu/grposters/42 11 Appendix A: Texas Bluebird Society Nest Box Heat Shield Plan Note: do not install front shield for Tree Swallow box. 12 Appendix I, Photo I : Nest box with heat shields to lower internal temperatures on hot days