HABITUATION
OF ADULT EASTERN NEST-BOX TRAP
BLUEBIRDS
TO
A
BY BENEDICT C. PINKOWSKI INTRODUCTION
A varietyof shuttertrapshavebeen recommendedfor capturingcavity-nestingbirds.Sometrapsare automaticand are triggeredwhen the bird entersthe nestcavity(DeHavenand Guarino,1969;Stewart,1971); othersare operatedmanuallyfrom a distanceby a string(Fischer,1944) or an electroniccontrol(Kibler, 1968;Dhondt and Van Outryve, 1971). When a conspicuous trap is placedon a nestsiteafter nestingis underway, the adult birds react initially with behaviorpatternssuchas escape (fleeing)and alarm notesthat are appropriateresponsesto a threat stimulus.A trappingattemptwill be successful only after a progressive reductionof the initial responseto the trap occurs,and sucha gradual reductionof a behavioralresponseattributableto an unreinforcedstimulus is commonlycalledhabituation(Vowlesand Prewitt, 1971). Informationon the rate at which adult birds habituateto traps placedon or near their nestswouldhelp banderseconomizetheir time and, in those instanceswhere both adult birds care for the young, it may permit some instructivecomparisons.
In thispaper I quantifythe reactionof adult EasternBluebirds(Sialia sialis)to a simple shutter-trap attached to nest boxes after the young had hatched.Both maleand femalebluebirdsfeed the youngalthough only the female broods(Hartshorne, 1962; Pinkowski,1978), and I examine trapping data on malesand femalesfor intersexualdifferences and suggesta regime for trapping both adultsat the nestwith a minimum
of disturbance. METHODS
AND
MATERIALS
Between6 May and 31 July in 1970 to 1977 I trappedbluebirdsfor bandingin nestboxeslocatedin MacombCo., Michigan.Detailsof the study area and a descriptionof the nest boxesare provided elsewhere (Pinkowski, 1975, 1976, 1977a, b).
The shutter-trap apparatus consistedof a small, teardrop-shaped pieceof plywoodmeasuring9 cm x 7 cm x 6 mm and operatedmanually by a string. The shutter was attachedto the nest box abovethe entranceby a tack insertedthrough a smallopeningin its narrow end. A secondtack that was attachedto the string held the shutter to one side of the entrance
until the bird entered
the nest box. I controlled
the
shutterwhile partiallyconcealedbehind vegetationat distancesof 40 to 60 m from
the nest box.
Many of the bluebirdsnestingin the study area had been banded previouslyas nestlings.As a result, often only one adult of a nesting pair wasunbandedand had to be captured.For eachcaptureI recorded the following information: (1) time required to capture the bird; (2) 125
126]
B. C. Pinkowski
Bird-Banding Spring 1978
adult enteringcavityfirst; and (3) number of entriesby one adult prior to capture of the other. Time required for capture consistedof the interval from when the trap wasin place(2 to 3 min after my arrival at a nest) until the bird entered the nest box. Both bluebirdsof a nesting pair becomesomewhatwary following the capture of one of the adults; therefore,I did not includedata obtainedon a secondbandingattempt that followedthe captureof one memberof a nestingpair earlier in the sameseason.Thus all tabulationsinvolvepairsinitiallyencounteringthe trapping apparatus.Trapping activitiesoccurredat all timesof day but were somewhatmore common at mid-morning than at other times. In eachcasethe weatherwasgenerallywarm and sunny. Frequenciesof occurrenceare examinedby Chi-squarecorrectedfor continuity,and times required for capture of malesand femalesare compared by the Mann-Whitney U-test. RESULTS
Of 63 trapping attemptson 30 malesand 33 females,only two were unsuccessful--the adult wasnot capturedafter 2 hr of trapping effort. Nearly all of the birds displayedalarm in responseto the trap. One female, however,unhesitatinglyentered a nestbox while I wassetting up the trap and was only 10 m from the nest. Initially a trap elicited fleeing behaviorand the adults were cautiousin approachingthe nest. After a time the adultswouldpeckaggressively at the shutterwhileatop the box or to the side of the entrance.A certain amount of fluttering in front of the entrancealmostalwaysprecededlandingat the entrance and entry. Occasionallyadults that were hesitantto approachthe nest box con-
sumed food items being carried to the young and then left to gather more food. One adult was more likely to enter the cavitywith food if the other adult wasnear the nestand not foraging somedistanceaway. If the male had food and the female did not, the female would often
"beg" and the male would transfer the food to her. The female would either eat the food herselfor enter the cavityand feed the young.OccasionallyI havealsoobservedthisbehaviorwhen non-humanpredators are near
a bluebird
nest.
The two birds that were not captured were both males.Femaleswere more likely to enter the nestbox first, entered more often during trapping attempts,and were captured in lesstime than males (Table 1). Usingthe variancesin the time required for captureparameter, I found that maleswere significantlymore variablein their responseto the trap than were females (F = 3.7, P < 0.001). Captured males required a maximum of 90 min to enter the nest box comparedwith a maximum of 57 min recorded
for females.
The different trapping ratesfor malesand femalesdid not appearto be attributableto sexualdifferencesin feeding and broodingfrequencies.Average agesof the nestlingswhen malesand femaleswere captured were 6.2 and 7.0 days,respectively.At this age youngbluebirds
Vol.49,No.2
Bluebirds andNest-box Traps T^•I.E
[127
1
Responseof male and female EasternBluebirdsto the shuttertrap. Male
No. timesentering first No. entries with trap in place
Mean time (min) required for capture
Female
P•
23
40
OF ADULT EASTERN NEST-BOX TRAP
BLUEBIRDS
TO
A
BY BENEDICT C. PINKOWSKI INTRODUCTION
A varietyof shuttertrapshavebeen recommendedfor capturingcavity-nestingbirds.Sometrapsare automaticand are triggeredwhen the bird entersthe nestcavity(DeHavenand Guarino,1969;Stewart,1971); othersare operatedmanuallyfrom a distanceby a string(Fischer,1944) or an electroniccontrol(Kibler, 1968;Dhondt and Van Outryve, 1971). When a conspicuous trap is placedon a nestsiteafter nestingis underway, the adult birds react initially with behaviorpatternssuchas escape (fleeing)and alarm notesthat are appropriateresponsesto a threat stimulus.A trappingattemptwill be successful only after a progressive reductionof the initial responseto the trap occurs,and sucha gradual reductionof a behavioralresponseattributableto an unreinforcedstimulus is commonlycalledhabituation(Vowlesand Prewitt, 1971). Informationon the rate at which adult birds habituateto traps placedon or near their nestswouldhelp banderseconomizetheir time and, in those instanceswhere both adult birds care for the young, it may permit some instructivecomparisons.
In thispaper I quantifythe reactionof adult EasternBluebirds(Sialia sialis)to a simple shutter-trap attached to nest boxes after the young had hatched.Both maleand femalebluebirdsfeed the youngalthough only the female broods(Hartshorne, 1962; Pinkowski,1978), and I examine trapping data on malesand femalesfor intersexualdifferences and suggesta regime for trapping both adultsat the nestwith a minimum
of disturbance. METHODS
AND
MATERIALS
Between6 May and 31 July in 1970 to 1977 I trappedbluebirdsfor bandingin nestboxeslocatedin MacombCo., Michigan.Detailsof the study area and a descriptionof the nest boxesare provided elsewhere (Pinkowski, 1975, 1976, 1977a, b).
The shutter-trap apparatus consistedof a small, teardrop-shaped pieceof plywoodmeasuring9 cm x 7 cm x 6 mm and operatedmanually by a string. The shutter was attachedto the nest box abovethe entranceby a tack insertedthrough a smallopeningin its narrow end. A secondtack that was attachedto the string held the shutter to one side of the entrance
until the bird entered
the nest box. I controlled
the
shutterwhile partiallyconcealedbehind vegetationat distancesof 40 to 60 m from
the nest box.
Many of the bluebirdsnestingin the study area had been banded previouslyas nestlings.As a result, often only one adult of a nesting pair wasunbandedand had to be captured.For eachcaptureI recorded the following information: (1) time required to capture the bird; (2) 125
126]
B. C. Pinkowski
Bird-Banding Spring 1978
adult enteringcavityfirst; and (3) number of entriesby one adult prior to capture of the other. Time required for capture consistedof the interval from when the trap wasin place(2 to 3 min after my arrival at a nest) until the bird entered the nest box. Both bluebirdsof a nesting pair becomesomewhatwary following the capture of one of the adults; therefore,I did not includedata obtainedon a secondbandingattempt that followedthe captureof one memberof a nestingpair earlier in the sameseason.Thus all tabulationsinvolvepairsinitiallyencounteringthe trapping apparatus.Trapping activitiesoccurredat all timesof day but were somewhatmore common at mid-morning than at other times. In eachcasethe weatherwasgenerallywarm and sunny. Frequenciesof occurrenceare examinedby Chi-squarecorrectedfor continuity,and times required for capture of malesand femalesare compared by the Mann-Whitney U-test. RESULTS
Of 63 trapping attemptson 30 malesand 33 females,only two were unsuccessful--the adult wasnot capturedafter 2 hr of trapping effort. Nearly all of the birds displayedalarm in responseto the trap. One female, however,unhesitatinglyentered a nestbox while I wassetting up the trap and was only 10 m from the nest. Initially a trap elicited fleeing behaviorand the adults were cautiousin approachingthe nest. After a time the adultswouldpeckaggressively at the shutterwhileatop the box or to the side of the entrance.A certain amount of fluttering in front of the entrancealmostalwaysprecededlandingat the entrance and entry. Occasionallyadults that were hesitantto approachthe nest box con-
sumed food items being carried to the young and then left to gather more food. One adult was more likely to enter the cavitywith food if the other adult wasnear the nestand not foraging somedistanceaway. If the male had food and the female did not, the female would often
"beg" and the male would transfer the food to her. The female would either eat the food herselfor enter the cavityand feed the young.OccasionallyI havealsoobservedthisbehaviorwhen non-humanpredators are near
a bluebird
nest.
The two birds that were not captured were both males.Femaleswere more likely to enter the nestbox first, entered more often during trapping attempts,and were captured in lesstime than males (Table 1). Usingthe variancesin the time required for captureparameter, I found that maleswere significantlymore variablein their responseto the trap than were females (F = 3.7, P < 0.001). Captured males required a maximum of 90 min to enter the nest box comparedwith a maximum of 57 min recorded
for females.
The different trapping ratesfor malesand femalesdid not appearto be attributableto sexualdifferencesin feeding and broodingfrequencies.Average agesof the nestlingswhen malesand femaleswere captured were 6.2 and 7.0 days,respectively.At this age youngbluebirds
Vol.49,No.2
Bluebirds andNest-box Traps T^•I.E
[127
1
Responseof male and female EasternBluebirdsto the shuttertrap. Male
No. timesentering first No. entries with trap in place
Mean time (min) required for capture
Female
P•
23
40
